Corporate Presentation

1. Horizon Pharmaplc
September 2017

2. Forward-Looking Statements
2
This presentation contains forward-looking statements, including, but not limited to, statements related to Horizon
Pharma's expected peak annual sales of its medicines, expected financial performance in future periods, expected
timing of clinical, regulatory and commercial events, including the planned Phase 3 clinical trial of teprotumumab
and clinical trials of ACTIMMUNE in cancer indications, any future strategic transactions and potential benefits
thereof, planned increases in KRYSTEXXA commercialization activities and resources, potential market opportunity
for Horizon Pharma’s medicines in approved and potential additional indications, potential growth of Horizon
Pharma’s medicines and markets, future debt payment obligations and business and other statements that are not
historical facts. These forward-looking statements are based on Horizon Pharma's current expectations and
inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially
from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which
include, without limitation, risks that Horizon Pharma’s actual future financial and operating results may differ from
its expectations or goals; Horizon Pharma’s ability to grow net sales from existing products; the availability of
coverage and adequate reimbursement and pricing from government and third-party payers and risks relating to
Horizon Pharma’s ability to successfully implement its business strategies; risks related to acquisition integration
and achieving projected benefits; risks associated with clinical development and regulatory approvals; risks in the
ability to recruit, train and retain qualified personnel; competition, including potential generic competition; the
ability to protect intellectual property and defend patents; regulatory obligations and oversight, including any
changes in the legal and regulatory environment in which Horizon Pharma operates, potential events that could
accelerate Horizon Pharma’s debt obligations and those risks detailed from time-to-time under the caption "Risk
Factors" and elsewhere in Horizon Pharma's filings and reports with the SEC. Horizon Pharma undertakes no duty
or obligation to update any forward-looking statements contained in this presentation as a result of new
information.

3. Horizon PharmaToday
WellPositionedforSustainableHighGrowth
3
• Diverse portfolio of high-growth rare disease medicines
• Building a pipeline to generate long-term value
• Proven acquisition capabilities, with expertise in identifying pipeline and on-market
medicine opportunities
• Differentiated and successful strategy that optimizes our medicines’ growth
trajectories through strong commercial execution and collaborative research
• Highly experienced management team
• Strong balance sheet that provides flexibility for strategic opportunities
Improving patients’ lives by identifying, developing, acquiring and
commercializing differentiated and accessible medicines that address
unmet medical needs

4. • TRIPLE trial
• Evaluating
immunomodulation
• Oncology combination-
therapy trials
Successful and proven
commercial execution that
optimizes the growth
trajectory of our
acquired medicines
Example:
Our Strategy
Create value by generating high growth and profitability of our rare disease medicines
Uniquely strong in-house
M&A capability
with proven track record
of execution
Growing pipeline of
differentiated and clinically
relevant medicines with a
focus on rare diseases
Maximizing the value of
our medicines through
portfolio expansion and
collaborative research
Examples: Example:
$0
$100
$200
$300
$400
2015
pre-acquisition
2017
2 years post
acquisition
>$400 peak
annual net sales
Teprotumumab
Examples:
 High unmet need; no
FDA-approved
therapies exist
 Impressive Phase 2
efficacy results
(p value ≤ 0.001)
 Phase 3 study is
confirmatory
 U.S. Orphan, Fast-Track
and Breakthrough
Therapy designations
4
KRYSTEXXANetSales(inmillions)
(1) Current Street consensus; not based on Horizon Pharma estimates.
(2) Projected; Horizon Pharma estimate.
(1) (2)

5. We Have Purposefully and Rapidly Transitionedtoa Rare
DiseaseMedicines Company…
5
July
2011
2011 -
2014
2014 -
2016
2017+
HZNP
Initial
Public
Offering
Developed a highly
successful commercial
business, generating
attractive growth and
cash flows to support
M&A and growth
initiatives
Built a stable base
of rare disease
growth assets
Continue the evolution to
generate long-term value
 Commercial execution
 Build development-stage
pipeline through M&A
 Prioritize pipeline assets
in addition to on-market
assetsTeprotumumab
Added high-growth
on-market and
pipeline rare
disease medicines
2016 -
2017

6. …Supported By Our Strong M&A Capability…
2010
2013
2014
2016
2014
2015
November 2013
Acquisition of VIMOVO
from AstraZeneca
October 2014
Acquisition of PENNSAID 2%
from Nuvo Research
April 2010
Acquisition
of Nitec Pharma
September 2014
Acquisition of Vidara
Therapeutics
May 2015
Acquisition of Hyperion
Therapeutics
(1) RAYOS is known as LODOTRA outside the United States. (2) VIMOVO was re-launched by Horizon sales force in January 2014. (3) PENNSAID 2% was re-launched by
Horizon sales force in January 2015. (4) BUPHENYL is known as AMMONAPS outside the United States. (5) The acquisition was completed on June 30, 2017. (6) Horizon
Pharma divested the marketing rights to PROCSYBI and QUINSAIR in Europe, the Middle East and Africa on June 23, 2017. Horizon Pharma retains marketing rights for the two
medicines in the U.S., Canada, Latin America and Asia. QUINSAIR is not approved in the United States.
January 2016
Acquisition of Crealta
2016
May 2016
Announcement of
acquisition of Global Rights
to IMUKIN (interferon
gamma-1b)
(1)
(2) (3)
(4)
(5)
2016
October 2016
Acquisition of Raptor
(6)
6
May 2017
Acquisition of River Vision
Development Corp.
Teprotumumab
Late-stage development biologic
2017
(6)

7. …Resulting in Annual Net Sales CAGR of 173%
$19
$74
$297
$757
$1,046
$0
$200
$400
$600
$800
$1,000
$1,200
FY 12 FY 13 FY 14 FY 15 FY 16
(1)
(1) 2016 Net Sales is an adjusted, non-GAAP measure; see reconciliation slides at the end of the presentation for a reconciliation of GAAP to non-GAAP measures.
7
NetSales(inmillions)

8. 2013
(Net Sales By Product)
First Half 2017
(Net Sales By Product)
11 Medicines; 6 for Rare Diseases
HorizonPharma’s Portfolio Then and Now
RapidTransitiontoRareDiseaseMedicinesFocusedCompany
8
2 Medicines
(1) PROCYSBI and QUINSAIR were acquired on Oct. 25, 2016. Horizon Pharma divested the marketing rights to PROCSYBI and QUINSAIR in Europe, the Middle East and Africa on
June 23, 2017. Horizon Pharma retains marketing rights for the two medicines in the U.S., Canada, Latin America and Asia. QUINSAIR is not approved in the United States.
(1)
(1)
Acquired teprotumumab, a late-stage biologic for thyroid eye disease, in Q2 2017

9. Our On-Market andIn-Development Rare Disease
Medicines
9
Biologic for treatment of
refractory chronic gout
Treatment of
urea cycle disorders
Treatment of
nephropathic cystinosis
Biologic for treatment of Chronic Granulomatous Disease (CGD),
an immunocompromised disease
(1) Horizon Pharma divested the marketing rights to PROCSYBI and QUINSAIR in Europe, the Middle East and Africa on June 23, 2017. Horizon Pharma retains marketing rights for
the two medicines in the U.S., Canada, Latin America and Asia. QUINSAIR is not approved in the United States.
Teprotumumab
Late-stage development biologic
candidate for treatment of thyroid
eye disease
(1)
(1)
Treatment of urea cycle disordersManagement of chronic pulmonary
infections in adult cystic fibrosis patients

10. KRYSTEXXA®
OurKeyGrowthDriverwithPotentialPeakSalesof>$400M(1)
• KRYSTEXXA indicated for refractory chronic gout(2), a rare disease
– KRYSTEXXA is the first and only biologic for refractory chronic gout patients that
rapidly reverses disease progression(3)
• 93% reduction in mean serum uric acid levels within 24 hours
following the first infusion
• 45% of subjects achieved complete resolution of target tophus,
with no progression at 6 months vs. placebo
– U.S. market
• >50,000 rheumatology patients have refractory chronic gout
• Nephrology patient population could be as large as rheumatology
– U.S. market growth rate
• 3-4 percent annually(3)
– Growth drivers
• Invest in and capitalize on expansion of commercial organization
• Invest in education as well as patient and physician outreach,
sharing robust safety and efficacy data from phase 3/4 trials
10
(1) Horizon estimate.
(2) See full prescribing information at www.KRYSTEXXA.com.
(3) Source: Adapted from Klippel 2008. Edwards NL. Gout. A. Clinical features. In: Klippel JH, Stone JH, Crofford LJ, White PH, eds. Primer on the Rheumatic Diseases. 13th ed.
New York: Springer; 2008:241-249. Tophus / tophi: uric acid deposits of uric around joints.

11. KRYSTEXXA is a Highly Effective Medicine
BeforeandAfterFiveMonthsofKRYSTEXXATherapy
11

12. The Right Strategyfor KRYSTEXXA…
Lack of disease awareness
resulted in lack of urgency
to treat
12
• Initiatededucationcampaigntobuildawarenessand
identifypatients
• “Allgoutistophaceous”messagelaunchedatACR
What We Saw In Jan. 2016… What We Have Done Since Then…
Poor working knowledge of
KRYSTEXXA
• Re-analyzedclinicaltrialdatawithafocusonsafetyand
socialized“stoppingrules”
• Improvingsafetyperceptionpositivelyimpactingefficacy
discussions
Misdirected and under-
resourced marketing and sales
created perception of
“difficult to use” drug
• Builtoutahighlyexperiencedsales,marketingandmedical
affairsteamtoappropriatelysupportpatientcommunity
andphysicians
• AnnouncedinMay2017increasedinvestmenttoaddress
significantopportunitytooptimizepeaksalespotentialin
rheumatologyandexpandintonephrology
ACR: American College of Rheumatology.

13. ACR
Relaunch
Patient Access
Managers Hired
Marketing Team Expansion
Clinical Trial Data Re-analyzed
Medical Scientific Liaison Team Expanded (1 to 10)
Key Opinion Leader Outreach Initiated
KRYSTEXXA Sales Force Expanded (15 to 43)
TRIPLE Investigator-initiated Trial Started
Original Crealta Resource Base
…Supported by IncreasedInvestments…
RaisedKRYSTEXXAPeakAnnualNetSalesEstimateto>$400Mfrom>$250M
13
Commercial
Clinical
KRYSTEXXA Growth Initiatives
2016
2017
Expanding Reach within Rheumatologists and Expanding into Nephrology
ACR: American College of Rheumatology.
Doubling Size of Commercial Operation – from >100 Employees to ~200

14. KRYSTEXXA Growth Initiatives
500
550
600
650
700
750
800
850
900
$10
$15
$20
$25
$30
$35
$40
Q1 16 Q2 16 Q3 16 Q4 16 Q1 17 Q2 17
Net sales Average monthly vials
…Has DrivenRapidly Accelerating VialGrowth
14
NetSales(inmillions)
AverageMonthlyVials
Acquired 1.13.2016
Q2 2017 KRYSTEXXA vial growth >40 percent year over year;
we expect continued strong demand going forward
Initial Investment
Typical Seasonality
Incremental
Investment

15. RAVICTI®
IncreasingPenetrationoftheTreatablePatientPopulation
• Indicated for Urea Cycle Disorders (UCDs)
– UCDs are rare and life-threatening genetic diseases resulting
in body’s inability to remove ammonia from the blood stream(1)
– U.S. market
• ~2,600 people with UCDs; ~1,000 treatable population
– U.S. market share
• ~47 percent of diagnosed patients
– Growth drivers
• Increase awareness and diagnosis of UCDs
• Drive conversion from older-generation nitrogen-scavengers to RAVICTI
15
(1) See full prescribing information at www.RAVICTI.com.
sNDA: Supplemental New Drug Application
Q2 2017 U.S. FDA approval of sNDA expands the age range
to ≥ 2 months of age and older from ≥ 2 years of age and older

16. • Indicated for nephropathic cystinosis (NC)(1)
– NC is a rare and life-threatening metabolic disorder
• Without treatment, high intracellular cystine concentrations can occur in virtually all
organs and tissues, leading to irreversible cellular damage, progressive multi-organ
failure and death
– U.S. market
• ~500-600 diagnosed patients; ~400-450 diagnosed patients on therapy
– U.S. market share
• ~53 percent of diagnosed patients(2)
– Growth drivers
• Drive conversion of patients from older-generation therapy
• Drive uptake of diagnosed but untreated patients
• Identify previously undiagnosed patients
PROCYSBI®
DrivingAdditionalUptake
16
(1) See full prescribing information at www.PROCYSBI.com.
(2) The methodology for calculating PROCYSBI market share was revised in Q2 2017 to be more consistent with the methodology used for RAVICTI® and ACTIMMUNE market share.
We now report the PROCYSBI market share of diagnosed patients versus diagnosed patients on therapy (treated patients). Under the previous methodology,
PROCSYBI market share would be ~71 percent.
Approved in Canada in Q2 2017;
only cystine-depleting agent approved for NC treatment

17. ACTIMMUNE®
EstablishingRoleofACTIMMUNEinBroaderRangeofPatients
• Treatment of CGD(1)
– CGD is an immune disease that leads to recurrent
severe bacterial and fungal infections(1)
– Patients have increased susceptibility to severe and recurrent
bacterial and fungal infections, along with the formation and
development of granulomas in most organs
– U.S. CGD market
• ~1,600 people
– U.S. market share
• ~17 percent of diagnosed patients
– Growth drivers
• Increase awareness and diagnosis of CGD
• Increase persistence (length of treatment)
17
(1) See full prescribing information at www.ACTIMMUNE.com.
CGD: Chronic Granulomatous Disease.

18. Primary Care Business Unit
• ManagingthePrimaryCarebusinessunitforcashflowtofurtherdiversifyinto
rarediseasemedicines
• Fourmedicines:
– DUEXIS®andVIMOVO®: indicatedfortreatmentofosteoarthritis(OA)and
rheumatoidarthritis(RA)
– PENNSAID®2%: indicatedfortreatmentofOAoftheknee
– MIGERGOT®: indicatedfortreatmentofmigraines
18
(1) PENNSAID 2% sold by both the Primary Care and Rheumatology sales forces.
(1)
(1)

19. Our Portfolio is Supportedby Our Intellectual Property
Expertise and Long-Life ProtectedPatents
19
Medicine Potential Exclusivity
• 5 OB listed patents extending to 2034
• Orphan Drug Exclusivity: U.S. 2020/2022; E.U. 2023
• 7 OB listed patents extending to 2032
• Orphan Drug Exclusivity to 2020
• 7 U.S. patents, 4 Canadian patents; not approved in U.S.
• 2 U.S. patents extending to 2022
• 16 U.S. patents extending to 2030
• Orphan Drug Exclusivity to 2017; Biologic Exclusivity to 2022
• 8 OB listed patents extending to 2028
• Settled Actavis (first-filer) litigation with right to market Dec. 23, 2022
• 14 OB listed patents (including esomeprazole patents) extending to 2031
• 10 OB listed patents (excluding esomeprazole patents) + 1 process patent
• In June 2017, U.S. District Court upheld both ‘285 patent (expires in 2022) and ‘907 patent
(expires 2023) in case against Dr. Reddy’s Laboratories, Mylan and Lupin
• 19 OB listed patents extending to 2030
• Settled Teligent, Amneal, Paddock (Perrigo) & Taro litigations by granting a right to market no sooner
than Jan. 10, 2029; litigation with Lupin pending
• In May 2017, U.S. District Court upheld ‘913 patent (expires in 2027) in case against Actavis
• 6 OB listed patents extending to 2026
• Settled Par (first-filer) litigation with right to market Jan. 1, 2023
OrphanPrimaryCareRheumatology
(1) Horizon Pharma divested the marketing rights to PROCSYBI and QUINSAIR in Europe, the Middle East and Africa on June 23, 2017. Horizon Pharma retains marketing
rights for the two medicines in the U.S., Canada, Latin America and Asia. QUINSAIR is not approved in the United States.
(1)
(1)

20. • Autosomal dominant osteopetrosis*
• Combo cancer therapy w/Opdivo®(3)*
• Combo cancer therapy w/Keytruda®(4)*
• Breast cancer combo cancer therapy(6)*
Post-
Market
Phase 3Phase 2Phase 1
• Label Expansion: UCD in patients
from birth to 2 months of age
• Lupus* (to address fatigue)
(1) Teprotumumab is a development-stage biologic and is not approved for use.
(2) Expect to begin Phase 3 study by year end.
(3) Registered trademark of Bristol-Myers Squibb.
(4) Registered trademark of Merck.
(5) Expect to initiate Phase 2 program by year end.
(6) Study with Taxol, Herceptin and Perjeta; Taxol is a registered trademark of Bristol-Meyers Squibb.
Herceptin and Perjeta are registered trademarks of Genentech.
We Are Driving Additional Growth With Our RareDisease
FocusedPipeline
• TRIPLE trial* to address immunogenicity
evaluating; initial dose, dosing frequency
and increased dose based on weight
Treatment / Trial ObjectiveMedicine
ACTIMMUNE®
RAVICTI®
KRYSTEXXA®
RAYOS®
20
(1)Teprotumumab • Moderate-to-severe thyroid eye disease
Rare Disease Medicine
Other
(2)
(5)
* Investigator-initiated trial.
Pre-
clinical
(1)

21. Teprotumumab
Late-StageDevelopment ProgramforThyroidEyeDisease(TED)
21
Overview
• Acquired May 2017 with acquisition of River Vision
• Fully human monoclonal antibody
• Expect to enter Phase 3 by year-end 2017
• Peak annual U.S. net sales potential of >$250M(1)
• First acquisition of a development-stage medicine for rare diseases
Strategic Benefits
• Expands and diversifies rare disease medicine pipeline
• Potential to expand Horizon Pharma’s served markets to include endocrinology
Target
Indication
• Moderate-to-severe Thyroid Eye Disease (TED), a debilitating autoimmune condition
commonly in patients with active Graves’ Disease
• Treated by endocrinologists and ophthalmologists
U.S. Population • ~10,000 patients in U.S. with moderate to severe disease; significant unmet need
Standard of Care
• No FDA-approved therapies; unapproved medication treatment modalities have
limited efficacy and safety concerns; surgery is invasive and complex
Development
Phase
• Phase 2 study completed; results published in May 2017 The New England Journal of Medicine
• Expect to begin Phase 3 confirmatory study by year-end 2017; similar design to Phase 2 study
Regulatory Status • U.S. FDA Orphan, Fast-Track and Breakthrough Therapy designations
U.S. Exclusivity • 12-year biologics exclusivity; 7-year orphan exclusivity, if approved
Rights • Worldwide, excluding oncology indications
(1) Horizon Pharma estimate.

22. Significant Unmet Need Exists for TED Patients
PainfulandDisfiguringDiseasewithNoFDA-ApprovedTherapies
22
• TED is a rare, painful
debilitating condition:
- Inflammation
- Proptosis (protrusion
of eyeball from
socket)
- Corneal ulceration
- Disfiguring, poor QoL,
emotionally
debilitating
• Standard of care is
unsatisfactory:
- No FDA-approved
therapies
- Steroids/rituximab
have limited efficacy
- Surgery is invasive,
complex and may only
result in partial
function
Orbital surgery
Clinical presentation of TED • Teprotumumab has the potential to be
first FDA-approved therapy for TED
• Mechanism of action
- Inhibits IGF-1R, blocking
underlying autoimmune
mechanism, de-activating
fibroblasts, resolving
inflammation, minimizing/
reversing tissue expansion
• Impressive efficacy in Phase 2 trial
- 69% of patients saw a reduction of
>2mm in proptosis AND reduction
>2 in clinical activity score (CAS)
(p<0.001)
- Rapid onset, with 43% response at
week 6 (p<0.001)
- Significant improvement in QoL
- Large safety data base exists
• Expect to begin Phase 3 confirmatory
trial by YE 2017 to obtain FDA approval
Current State of TED Potential Impact of Teprotumumab
Note: QoL: Quality of Life.

23. 23
Primary
Endpoint
Patient-
Reported
Endpoint
(Secondary)
• Multi-center, double-blind, randomized placebo-controlled study
• Designed to determine efficacy and safety of teprotumumab
• 24-week dosing period; 12-month follow-up; infused every 3 weeks
• 88 patients with recent onset, moderate-to-severe TED across 15 sites
• Response of the study eye, defined as a reduction in CAS (Clinical Activity Score) of
> 2 points and a reduction of proptosis of > 2mm, at 24 weeks
• Clinical Activity Score (CAS):
– CAS has scores from 0-7, with > 3 indicating active TED
– For Phase 2 study, CAS measured change in orbital inflammation and pain
– Baseline CAS for teprotumumab was 5.1 points
– Local inflammation in soft tissues of orbit is a key driver of pain, swelling
– Blocking inflammation important for preventing disease progression
• Proptosis: protrusion of the eyeball from the socket
– Result of soft tissue deposition behind the eye
– Painful, impairs full lid closure, and can cause corneal ulceration
– Associated with sight-threatening optic neuropathy
• Quality of life (GO-QoL questionnaire)
– Two subscales: visual function and appearance
– Compromised vision impairs normal daily activities
– Profound changes in appearance cause psychosocial distress
TeprotumumabPhase 2 ClinicalTrial Design
Study
Design
Note: GO-QoL: Graves’ Ophthalmology Quality of Life Scale.

24. TeprotumumabPhase 2 Results
PublishedinTheNewEnglandJournalofMedicineonMay4,2017
24
“In conclusion, a 24-week course of teprotumumab therapy provided clinical benefit
in patients with active, moderate-to-severe thyroid-associated ophthalmopathy by reducing
proptosis and the Clinical Activity Score and by improving the patients’ quality of life.”(1)
The New England Journal of Medicine, 376;18, www.nejm.org, May 4, 2017.
Thyroid eye disease (TED) is also known as thyroid-associated ophthalmopathy.

25. TeprotumumabPhase 2 Results:Overview
25
Efficacy
• Unprecedented clinical efficacy in TED
• Primary endpoint: response in study eye, defined as reduction of > 2
points in Clinical Activity Score and > 2 mm in proptosis at week 24
– Clinically meaningful and statistically significant improvement at week 24
– Marked improvement in CAS and proptosis vs. placebo
(69% vs. 20%, p ≤ 0.001)
– Therapeutic effects were rapid, at week 6, 43% of teprotumumab
patients vs. 4% of placebo patients had a response (p ≤ 0.001)
– Improvements continued through treatment period
• Secondary endpoint: significant improvement in quality of life
Safety
• Well tolerated; majority of adverse events mild
– In diabetic patients, hyperglycemia was the only drug-related adverse
event; controlled by adjusting diabetes medications
• Large safety database (including Roche oncology program)
TED: Thyroid eye disease, also referred to as thyroid-associated ophthalmopathy.
CAS: Clinical Activity Score; scores range from 0 to 7, with a score of > 3 indicating active TED.

26. TeprotumumabPhase 2 Results:
BaselineChangeofProptosisandClinicalActivityScore;ResponseRate
26
Source: The New England Journal of Medicine, 376;18, www.nejm.org, May 4, 2017.
CAS: Clinical Activity Score.
Proptosis: Teprotumumab Patients
Demonstrated Significant
Reduction vs Placebo Patients
CAS: Teprotumumab Patients
Demonstrated Greater Reduction
vs Placebo Patients
Response Rate: Teprotumumab
Patients Demonstrated Rapid Onset
of Response vs Placebo Patients

27. KRYSTEXXA® DevelopmentPrograms
• Working to address immunogenicity through investigator-initiated TRIPLE trial; also
evaluating other strategies, including immunomodulation
• TRIPLE trial studying approach for reducing loss of efficacy due to immunogenicity
– Assessing a reduction in immunogenicity following an increase in dosing frequency
– Also evaluating other subpopulations, including patients with increased body weight
• Data presented at scientific meetings to expand awareness among rheumatologists of
KRYSTEXXA as a safe and effective treatment for refractory chronic gout
– European League Against Rheumatism (EULAR) Annual European Congress of
Rheumatology – June 2017: 7 abstracts 4 presentations
• Gout patient hospitalizations have increased >400 percent since 1993,
and resulted in >$42.6 billion of healthcare costs in 2014 alone(1)
• Data show benefit of KRYSTEXXA regardless of clinically apparent tophi
– American College of Rheumatology (ACR) meeting – November 2016
• 25 percent of “non-responders” taking KRYSTEXXA reported complete tophus resolution
at 6 months
(1) Source: “Not Just a Swollen Big Toe: Increasing All-Cause Hospitalizations in Patients with Gout in the United States: 1993-2014”; study presented at 2017 EULAR Annual
European Congress of Rheumatology, June 15, 2017; abstract THU0409.
Please see full prescribing information, available at www.KRYSTEXXA.com.27

28. • ACTIMMUNE (interferon gamma-1b)
– PD-1 and PD-L1 inhibitors are considered among the most promising breakthroughs in
cancer therapy
– Analysts project PD-1 and PD-L1 checkpoint inhibitor’s market >$30 billion
• Three investigator-initiated trials underway to study ACTIMMUNE as an immune booster in cancer
combination studies
– Moffitt Cancer Center and Research Institute: Enrolling patients
• Study focus is to determine the optimal dosing for combination therapy of
ACTIMMUNE with Taxol®(1) (paclitaxel), Herceptin®(3) (trastuzumab) and
Perjeta®(3) (pertuzumab) for treatment of certain advanced breast cancer patients
– Fox Chase Cancer Center: Enrolling patients in the fourth cohort; expect results later in 2017
• Study focus is on the combination of ACTIMMUNE with
Opdivo®(1) (nivolumab), a PD-1 inhibitor for treatment of cancer
• Phase 1 data presented in Q1 2017 showed that the combination
therapy was safe and well-tolerated in the first two cohorts
– National Cancer Institute: Phase 2 study on track to begin later in 2017
• Study focus is on combination therapy of ACTIMMUNE with
Keytruda®(2) (pembrolizumab), a PD-1 inhibitor for treatment of cancer
ACTIMMUNE® Development Programs
ACTIMMUNEMayPromote/EnhanceEffectofPD-1/PD-L1Inhibitors
28
(1) Registered trademark of Bristol-Myers Squibb. (2) Registered trademark of Merck. (3) Registered trademark of Genentech.

29. Significant Developments YTD 2017
• Acquired teprotumumab, a late-stage development biologic, expanding our
orphan pipeline to include development-stage compounds
• Presented four new KRYSTEXXA® data analyses at 2017 EULAR
• Initiated expansion of KRYSTEXXA commercial organization
• Received U.S. FDA approval for sNDA for expanded age range for RAVICTI®
• Received Health Canada approval of PROCYSBI®
• Continued progress with ACTIMMUNE and cancer combination therapy studies
• Divested the marketing rights for PROCYSBI and QUINSAIR™ in EMEA
• Successfully defended patents for PENNSAID® 2% and VIMOVO®
29
We are advancing our strategy to expand our rare disease business, drive
commercial execution and build a pipeline of development-stage medicines
sNDA: Supplemental New Drug Application.
EMEA: Europe, Middle East and Africa; EULAR: European League Against Rheumatism; FDA: (U.S.) Food and Drug Administration.

30. We’ve Grown Our Cash Flows and Deployed Them
Into Growing Our Rare Disease Medicines
30
(in thousands)
Adjusted Operating Cash Flow(1)
($100,000)
$0
$100,000
$200,000
$300,000
$400,000
$500,000
2012 2013 2014 2015 2016
(1) The Operating Cash Flow for 2014, 2015 and 2016 are adjusted, non-GAAP measures; see reconciliation slides at the end of the presentation for a reconciliation of
GAAP to non-GAAP measures. The Operating Cash Flow for 2012 and 2013 are presented on a GAAP basis.

31. Our Strong Financial PositionSupports
Our Growth Strategy
31
June 30,
2017
Cash and cash equivalents $554
Senior secured term loans – due 2024 848
Senior notes – due 2023 475
Senior notes – due 2024 300
2.5% exchangeable senior notes – due 2022 400
Total debt $2,023
($ in millions)
* Senior Secured Term Loans schedule includes 1 percent annual amortization ($8.5M of principal).
Note: Adjusted EBITDA is a non-GAAP measure; see reconciliation slides at the end of the presentation for a reconciliation of GAAP to non-GAAP measures.
LTM: last twelve months.
EBITDA: earnings before interest, tax, depreciation and amortization.
Cash and cash equivalents of $554.3 million at June 30, 2017;
net debt to LTM adjusted EBITDA leverage ratio of 3.2 times
Our strong cash flow and balance sheet give us flexibility
to consider strategic opportunities that support our growth strategy
Debt Repayment Schedule:
5+ Years Until First Maturity

32. Horizon PharmaToday
WellPositionedforSustainableHighGrowth
32
• Diverse portfolio of high-growth rare disease medicines
• Building a pipeline to generate long-term value
• Proven acquisition capabilities, with expertise in identifying pipeline and on-market
medicine opportunities
• Differentiated and successful strategy that optimizes our medicines’ growth
trajectories through strong commercial execution and collaborative research
• Highly experienced management team
• Strong balance sheet that provides flexibility for strategic opportunities
Improving patients’ lives by identifying, developing, acquiring and
commercializing differentiated and accessible medicines that address
unmet medical needs

33. Horizon Pharmaplc
September 2017

34. Note Regarding Use of Non-GAAPFinancialMeasures
EBITDA, or earnings before interest, taxes, depreciation and amortization, adjusted EBITDA; adjusted net sales and adjusted operating
cash flows are used and provided by Horizon Pharma as non-GAAP financial measures. These non-GAAP measures are intended to
provide additional information on Horizon Pharma’s performance, operations, expenses, profitability and cash flows. Adjustments to
Horizon Pharma's GAAP figures as well as EBITDA exclude acquisition-related expenses, charges related to the discontinuation of
ACTIMMUNE development for Friedreich’s ataxia, an upfront fee for a license of a patent, a litigation settlement, loss on debt
extinguishment and loss on sale of long-term investments, costs of debt refinancing, drug manufacturing harmonization costs, as well as
non-cash items such as share-based compensation, depreciation and amortization, royalty accretion, non-cash interest expense,
intangible and other non-current asset impairment charges, and other non-cash adjustments. Certain other special items or substantive
events may also be included in the non-GAAP adjustments periodically when their magnitude is significant within the periods incurred.
Horizon Pharma maintains an established non-GAAP cost policy that guides the determination of what costs will be excluded in non-
GAAP measures. Horizon Pharma believes that these non-GAAP financial measures, when considered together with the GAAP figures,
can enhance an overall understanding of Horizon Pharma's financial and operating performance. The non-GAAP financial measures are
included with the intent of providing investors with a more complete understanding of the Company’s historical and expected 2017
financial results and trends and to facilitate comparisons between periods and with respect to projected information. In addition, these
non-GAAP financial measures are among the indicators Horizon Pharma's management uses for planning and forecasting purposes and
measuring the Company's performance. For example, adjusted EBITDA is used by Horizon Pharma as one measure of management
performance under certain incentive compensation arrangements. These non-GAAP financial measures should be considered in addition
to, and not as a substitute for, or superior to, financial measures calculated in accordance with GAAP. The non-GAAP financial measures
used by the Company may be calculated differently from, and therefore may not be comparable to, non-GAAP financial measures used by
other companies.
34

35. GAAP to Non-GAAPReconciliation
NetSalesandAdjustedNetSales(YearEnded2016)
35
(in millions except for percentages) Q4 16 Q4 15
%
Change FY 16 FY 15
%
Change
Orphan 88.1$ 68.2$ 29 299.3$ 207.8$ 44
RAVICTI®(1)
32.9 34.5 (4) 151.5 86.9 74
ACTIMMUNE® 24.2 28.1 (14) 104.6 107.4 (3)
BUPHENYL®(1)
4.7 5.6 (16) 16.9 13.5 25
PROCYSBI®(3)
25.3 - NM 25.3 - NM
QUINSAIRTM(3)
1.0 - NM 1.0 - NM
Rheumatology 41.6 13.5 208 142.7 45.2 215
KRYSTEXXA®(2)
29.5 - NM 91.1 - NM
RAYOS® 11.3 11.1 1 47.4 40.3 17
LODOTRA® 0.8 2.4 (67) 4.2 4.9 (14)
Primary Care 180.6 162.8 11 604.1 504.0 20
PENNSAID® 2% 96.6 55.4 74 304.4 147.0 107
DUEXIS® 50.9 60.4 (16) 173.7 190.4 (9)
VIMOVO® 31.6 47.0 (33) 121.3 166.6 (27)
MIGERGOT®(2)
1.5 - NM 4.7 - NM
Litigation settlement(4)
- - NM (65.0) - NM
Total GAAP net sales(4)
310.3$ 244.5$ 27 981.1$ 757.0$ 30
Total non-GAAP adjusted net sales(4)
310.3$ 244.5$ 27 1,046.1$ 757.0$ 38
(1) RAVICTI and BUPHENYL were acquired on May 7, 2015.
(2) KRYSTEXXA and MIGERGOT were acquired on January 13, 2016.
(3) PROCYSBI and QUINSAIR were acquired on October 25, 2016.
(4) On Sept. 26, 2016, Horizon Pharma agreed to pay Express Scripts $65 million as part of a litigation settlement, which was recorded as a
one-time reduction to GAAP net sales for the twelve months ended December 31, 2016, in accordance with U.S. GAAP. The exclusion
of the $65 million settlement from GAAP net sales is the only adjustment reflected in year-to-date non-GAAP adjusted net sales.

36. Confidential Information – Horizon Pharma plc
GAAP to Non-GAAPReconciliation
OperatingCashFlowandAdjustedOperatingCashFlow
36

37. GAAP to Non-GAAPReconciliation
EBITDAandAdjustedEBITDA(SixMonthsEndedJune30,2017)
37
2017 2016 2017 2016
EBITDA and Adjusted EBITDA:
GAAP net (loss) income (209,536)$ 14,984$ (300,106)$ (30,422)$
Depreciation 1,755 1,091 3,561 2,083
Amortization, accretion and step-up:
Intangible amortization expense 69,776 50,792 139,453 100,442
Accretion of royalty liabilities 12,735 9,669 25,694 19,028
Amortization of deferred revenue (207) (213) (411) (419)
Inventory step-up expense 33,895 9,102 74,490 16,548
Interest expense, net (including amortization of
debt discount and deferred financing costs) 31,608 19,228 63,591 38,686
Benefit for income taxes (1,767) (2,756) (49,320) (4,199)
EBITDA (61,741)$ 101,897$ (43,048)$ 141,747$
Non-GAAP adjustments:
Remeasurement of royalties for medicines acquired through business combinations - - (2,944) -
Acquisition-related costs 153,385 281 163,424 11,297
Upfront fee for license of global patent - - - 2,000
Primary Care business unit realignment costs 5,193 - 5,193 -
Gain on divestiture (5,856) - (5,856) -
Loss on debt extinguishment - - 533 -
Fees related to term loan refinancing (45) - 4,098 -
Share-based compensation 27,768 27,997 56,237 55,609
Charges relating to discontinuation of Friedreich's ataxia program 19,167 - 19,167 -
Drug substance harmonization costs 745 - 5,044 -
Royalties for medicines acquired through business combinations (11,622) (9,095) (22,939) (17,595)
Total of Non-GAAP adjustments 188,735 19,183 221,957 51,311
Adjusted EBITDA 126,994$ 121,080$ 178,909$ 193,058$
Three Months Ended June 30, Six Months Ended June 30,

38. GAAP to Non-GAAPReconciliation
EBITDAandAdjustedEBITDA(ThreeMonthsEndedDecember31,2016)
38
2016 2015 2016
EBITDA and Non-GAAP EBITDA:
GAAP net (loss) income (130,542)$ 23,994$ (166,834)$ $
Depreciation 1,696 2,612 4,962
Amortization, accretion and step-up:
Intangible amortization expense 65,676 41,706 216,875
Accretion of royalty liabilities 11,854 6,517 40,616
Amortization of deferred revenue (205) (208) (836)
Inventory step-up expense 43,284 860 71,137
Interest expense, net (including amortization of
debt discount and deferred financing costs) 28,858 20,120 86,610
(Benefit) expense for income taxes (29,305) (35,456) (61,251)
EBITDA (8,684)$ 60,145$ 191,279$ $
Non-GAAP adjustments:
Remeasurement of royalties for medicines acquired through business combinations 386 6,874 386
Acquisition-related costs 36,418 7,380 52,874
Upfront fee for license of global patent - - 2,000
Loss on sale of long-term investments - 29,032 -
Loss on induced conversion of debt and debt extinguishment - - -
Share-based compensation 29,223 27,990 114,144
Litigation settlement - - 65,000
Reversal of pre-acquisition reserve upon signing of contract - - (6,900)
Impairment of in-process research and development 66,000 - 66,000
Charges relating to discontinuation of Friedreich's ataxia program 23,513 - 23,513
Royalties for medicines acquired through business combinations (1) (10,434) (8,944) (37,593)
Total of Non-GAAP adjustments 145,106 62,332 279,424
Adjusted EBITDA 136,422$ 122,477$ 470,703$ $
Three Months Ended December 31, Twelve Months Ended D

39. GAAP to Non-GAAPReconciliation
EBITDAandAdjustedEBITDA(ThreeMonthsEndedSeptember30,2016)
39
2016 2015 2016
EBITDA and adjusted EBITDA:
GAAP Net (Loss) Income (5,870)$ 3,277$ (36,292)$
Depreciation 1,183 1,578 3,266
Amortization and accretion:
Intangible amortization expense 50,757 41,707 151,199
Accretion of royalty liabilities 9,734 6,551 28,762
Amortization of deferred revenue (212) (490) (631)
Amortizaton of inventory step-up adjustment 11,305 4,140 27,853
Interest expense, net (including amortization of
debt discount and deferred financing costs) 19,066 20,300 57,752
(Benefit) expense for income taxes (27,747) 21,979 (31,946)
EBITDA 58,216$ 99,042$ 199,963$
Non-GAAP adjustments:
Remeasurement of royalties for medicines acquired through business combinations - - -
Acquisition-related costs 5,159 14,498 16,456
Upfront fee for license of global patent - - 2,000
Loss on induced conversion of debt and debt extinguishment - - -
Share-based compensation 29,312 26,457 84,921
Litigation settlement 65,000 - 65,000
Reversal of pre-acquisition reserve upon signing of contract (6,900) - (6,900)
Royalties for medicines acquired through business combinations (9,564) (8,854) (27,159)
Total of Non-GAAP adjustments 83,007 32,101 134,318
Adjusted EBITDA 141,223$ 131,143$ 334,281$
Three Months Ended September 30, Nine Months En

40. Horizon Pharmaplc
September 2017