What rare diseases does Horizon Therapeutics focus on?

Horizon Therapeutics has active programs across 6 rare diseases: Chronic Granulomatous Disease, IgG4-Related Disease, Myasthenia Gravis, Neuromyelitis Optica, Thyroid Eye Disease, Urea Cycle Disorders. Each disease page on Trial Friend shows the latest recruiting trials, FDA-approved treatments, and patient resources.

Is Horizon Therapeutics focused exclusively on rare diseases?

Yes. Horizon Therapeutics is a rare disease specialist headquartered in Dublin, Ireland, founded in 2008. The company focuses primarily on developing treatments for rare and orphan diseases, with programs targeting Chronic Granulomatous Disease, IgG4-Related Disease, Myasthenia Gravis among others. It operates as part of Amgen.

How can I find Horizon Therapeutics clinical trials for rare diseases?

The clinical trials section on this page shows active and recruiting rare disease trials sponsored by Horizon Therapeutics, pulled live from ClinicalTrials.gov. Each trial card includes the study phase, recruitment status, conditions being studied, number of trial sites, and a direct link to the full study record. You can also explore individual disease pages to see trials from all sponsors for a specific condition.

How do I enroll in a Horizon Therapeutics clinical trial?

To explore enrollment, find a recruiting trial in the clinical trials list on this page and click "View full study" to see the full ClinicalTrials.gov record, which includes eligibility criteria, study locations, and contact information for each trial site. Your doctor can also help determine if a specific trial is appropriate for your condition. Not all trials are open at every location, so check the site list for one near you.

What FDA-approved rare disease drugs does Horizon Therapeutics have?

Horizon Therapeutics has 6 FDA-approved drugs with a rare disease use that we track, as of November 2026. ACTIMMUNE (interferon gamma-1b), approved 1999: Chronic Granulomatous Disease. BUPHENYL (sodium phenylbutyrate), approved 1996: Urea Cycle Disorders. PROCYSBI (cysteamine bitartrate), approved 2013: Cystinosis. Ravicti (glycerol phenylbutyrate), approved 2013: Urea Cycle Disorders. TEPEZZA (teprotumumab), approved 2020: Thyroid Eye Disease. UPLIZNA (inebilizumab), approved 2020: Myasthenia Gravis, Neuromyelitis Optica, IgG4-Related Disease. Source: the FDA's openFDA label database, matched to the rare diseases on Trial Friend; the list updates automatically and can include older products.

When was Horizon Therapeutics founded and where is it based?

Horizon Therapeutics was founded in 2008 and is headquartered in Dublin, Ireland. The company has been active for 18 years. It is a subsidiary of Amgen. As a rare disease specialist, the company dedicates its resources to developing therapies for patients with rare and orphan conditions.

Horizon Therapeutics

Rare disease drugmaker · part of Amgen · based in Dublin, Ireland · founded 2008 · amgen.com

Horizon Therapeutics works on 6 rare diseases we track, including Chronic Granulomatous Disease, IgG4-Related Disease and 4 more. It has 1 active clinical trial, though none is looking for new volunteers right now. It also has 7 FDA-approved rare disease drugs.

Horizon Therapeutics is now part of Amgen, which completed its $27.8 billion purchase of the company on October 6, 2023. Its medicines for rare autoimmune and severe inflammatory diseases are now in Amgen's portfolio.

Horizon Therapeutics pipeline

Each row lists the diseases Horizon Therapeutics is studying at that stage, from the ones closest to approval down to the earliest work.

Approved

Drugs the FDA has approved.

Actimmune (interferon gamma-1b) · Buphenyl (sodium phenylbutyrate) · Krystexxa (pegloticase) · Procysbi (cysteamine bitartrate) · Ravicti (glycerol phenylbutyrate) · Tepezza (teprotumumab) · Uplizna (inebilizumab)

Phase 1

First studies in people, mostly checking safety.

STXBP1 Encephalopathy With Epilepsy, SLC6A1 Neurodevelopmental Disorder

Horizon Therapeutics clinical trials

These are Horizon Therapeutics trials for the rare diseases we track, from ClinicalTrials.gov. Statuses there can lag behind company news, so confirm with the study team before you plan around one.

1 trial underway, not taking new volunteers

Underway, not taking new volunteersEarly Phase 1No updates in a whileNCT04937062

Phenylbutyrate for Monogenetic Developmental and Epileptic Encephalopathy

Tests Glycerol Phenylbutyrate 1100 MG/ML [Ravicti]

For STXBP1 Encephalopathy With Epilepsy, SLC6A1 Neurodevelopmental Disorder and Developmental and Epileptic Encephalopathy

This study is to evaluate the use of glycerol phenylbutyrate for monogenetic developmental epileptic encephalopathies (DEEs). DEEs are characterized by epilepsy and developmental delay in early life. Two examples of DEEs are STXBP1 and SLC6A1, though there are dozens of others. STXBP1 Encephalopathy is a severe disease that can cause seizures and developmental delays in infants and children. SLC6A1 neurodevelopmental disorder is characterized by developmental delay and often epilepsy. Both STXBP1 encephalopathy and SLC6A1 neurodevelopmental disorder cause symptoms because there are not enough working proteins made by these genes. It is possible that a medication called phenylbutyrate may help the the remaining proteins work better for STXBP1, SLC6A1, and/or other similar DEEs caused by single genes (i.e. "monogenetic"). This study is to test if glycerol phenylbutyrate is safe and well tolerated in children with monogenetic DEE.

Ages 0 Months - 17 Years2 locations

View full study

Ask about Horizon Therapeutics's trials

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Follow a condition Horizon Therapeutics is studying

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Condition to follow

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Trial Alerts, when a new trial opens or a trial changes
Disease Updates, FDA decisions and condition news, usually 1 or 2 emails a month

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FDA-approved drugs from Horizon Therapeutics

From the openFDA database. Tap a drug for side effects, dosing and help paying.

Actimmune interferon gamma-1b

For Chronic Granulomatous Disease. Approved Feb 25, 1999. Taken by subcutaneous route.

Buphenyl sodium phenylbutyrate

For Urea Cycle Disorders. Approved Apr 30, 1996. Taken by mouth.

Krystexxa pegloticase

Approved Sep 14, 2010. Taken by intravenous route.

Procysbi cysteamine bitartrate

For Cystinosis. Approved Apr 30, 2013. Taken by mouth.

Ravicti glycerol phenylbutyrate

For Urea Cycle Disorders. Approved Feb 1, 2013. Taken by mouth.

Tepezza teprotumumab

For Thyroid Eye Disease. Approved Jan 21, 2020. Taken by intravenous route.

Uplizna inebilizumab

For Myasthenia Gravis, Neuromyelitis Optica and IgG4-Related Disease. Approved Jun 11, 2020. Taken by intravenous route.

More about Horizon Therapeutics

They include Tepezza (teprotumumab) for thyroid eye disease, Krystexxa (pegloticase) for chronic gout that has not responded to standard treatment, Ravicti (glycerol phenylbutyrate) and Buphenyl (sodium phenylbutyrate) for urea cycle disorders, Actimmune (interferon gamma-1b) for chronic granulomatous disease, and Procysbi (cysteamine bitartrate) for nephropathic cystinosis. Uplizna (inebilizumab) is approved for neuromyelitis optica spectrum disorder, and since 2025 for IgG4-related disease and generalized myasthenia gravis.

Where Horizon Therapeutics trials take place

The trials above run at 2 study sites in 1 country. Tap a country to see its states, cities and hospitals.

United States

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Rare diseases Horizon Therapeutics works on

Each disease page lists every open trial, not only Horizon Therapeutics's, plus approved treatments.

Chronic Granulomatous Disease

Chronic granulomatous disease is a rare inherited immunodeficiency affecting the ability of neutrophils to produce reactive oxygen species.

How common: 1 in 250,000 people; X-linked form (most common) and autosomal recessive variants

IgG4-Related Disease

IgG4-related disease is a chronic fibroinflammatory condition characterized by tumor-like swelling in affected organs, dense lymphoplasmacytic infiltration rich in IgG4-positive plasma cells...

How common: Approximately 5 in 100,000 people; an estimated 57,000 diagnosed individuals in the U.S. as of 2024

Myasthenia Gravis

Myasthenia gravis is a chronic autoimmune neuromuscular disorder causing muscle weakness and rapid fatigue.

How common: 1 in 5,000 people

Neuromyelitis Optica

Neuromyelitis Optica (NMO) is a rare inflammatory autoimmune disorder of the central nervous system characterized by recurrent attacks of optic neuritis (vision loss) and acute myelitis (spinal cord...

How common: About 1 to 2 per 100,000 people worldwide, according to MedlinePlus Genetics

Thyroid Eye Disease

Thyroid eye disease (TED) is a rare autoimmune condition in which the immune system attacks the muscles and fat behind the eyes, causing bulging eyes, double vision, pain, and in severe cases vision...

How common: About 16 in 100,000 women and 3 in 100,000 men diagnosed each year; up to half of people with Graves' disease develop some degree of TED

Urea Cycle Disorders

Urea Cycle Disorders (UCDs) are a group of genetic conditions affecting the enzymes that convert toxic ammonia to urea for excretion.

How common: About 1 in 35,000 births in the United States, based on newborn screening and registry data (Summar et al., 2013); Ornithine Transcarbamylase (OTC) deficiency is most common form

Where to get support

Patient groups can explain a diagnosis, point you to specialists and tell you about trials before they open. Horizon Therapeutics's own site is amgen.com, and our help paying for treatment page lists drugmaker programs and charity funds.

NIH GARD - Chronic Granulomatous Disease
Chronic Granulomatous Disease and IgG4-Related Disease and 1 more
CGD Society
Chronic Granulomatous Disease
IgG4ward! Foundation
IgG4-Related Disease
Myasthenia Gravis Foundation of America (MGFA)
Myasthenia Gravis
Siegel Rare Neuroimmune Association (SRNA) - NMOSD
Neuromyelitis Optica
National Center for Advancing Translational Sciences (NCATS)
Neuromyelitis Optica
National Organization for Rare Disorders (NORD) - Thyroid Eye Disease
Thyroid Eye Disease
American Thyroid Association
Thyroid Eye Disease