Opsumit (Macitentan) – Oral


Opsumit may cause serious birth defects or fetal harm if taken during pregnancy. 

Use two acceptable methods of contraception to prevent pregnancy during and one month after treatment. Due to fetal risks, women can only receive the medicine through the Opsumit Risk Evaluation and Mitigation Strategy (REMS) program. Talk to your healthcare provider or pharmacist about these risks and how to use the medication safely.

What Is Opsumit?

Opsumit (macitentan) is an oral prescription medication used to treat pulmonary arterial hypertension, which is high blood pressure in the blood vessels of the lungs. It belongs to a class of drugs called endothelin receptor antagonists (ERAs).

Opsumit blocks endothelin-1 (ET-1) activity in the vascular endothelium (a layer of the inner cellular lining of blood vessels) and the smooth muscle in your lungs. Endothelin is a type of protein in your body that usually tightens your blood vessels and raises blood pressure.

By blocking ET-1, Opsumit helps relax the arteries, improves blood flow, and lowers blood pressure in the arteries of the lungs. As a result, your lungs receive more oxygen, allowing you to breathe more easily.

For women with PAH, Opsumit is only available through a special program called Risk Evaluation and Mitigation Strategy (REMS). You must be registered in the program and understand the risks and benefits of taking this medication. Talk to your healthcare provider for more information.

Opsumit is available in tablet form.

Drug Facts

Generic Name: Macitentan

Brand Name(s): Opsumit

Drug Availability: Prescription

Administration Route: Oral

Therapeutic Classification: Endothelin receptor antagonist

Available Generically: No

Controlled Substance: N/A

Active Ingredient: Macitentan

Dosage Form(s): Tablet

What Is Opsumit Used For?

The Food and Drug Administration (FDA) approved Opsumit to treat PAH in adults. It's meant to improve symptoms and keep your condition from worsening.

PAH is one type of pulmonary hypertension (PH). PAH may also be called primary pulmonary hypertension, which is often known as Group 1 PH based on the World Health Organization (WHO) classifications.

PAH occurs when the arteries in your lungs (pulmonary arteries) narrow, resulting in a higher pressure that prevents your blood from flowing through the blood vessels (arteries). This narrowing may result from the thickening or hardening of the arterial wall. 

How to Take Opsumit

Typical dosing is 10 milligrams by mouth once a day. You may take this medicine with or without food. Swallow the medicine whole and do not break, chew, or crush the tablet.

Before taking this medication, you must take a pregnancy test to ensure you aren't pregnant. Opsumit can harm the fetus, even during early pregnancy. You will be required to take a pregnancy test each month during treatment. Additionally, you should use two types of effective birth control while on Opsumit and for one month after your last dose.

Tell your healthcare provider right away if you think you are pregnant, planning to become pregnant, or are unable to use two forms of birth control. 

Follow your prescribing healthcare provider's directions on how to take Opsumit. Do not take this drug in larger or smaller amounts than prescribed or for longer than recommended.


Store Opsumit at room temperature (between 68 and 77 degrees F). Keep all of your medication out of the reach of children and pets to prevent accidental consumption.

How Long Does Opsumit Take to Work?

Studies have shown that people taking Opsumit had improved the blood flow in their lungs and were able to walk longer distances after 16 weeks (four months). However, this might differ from person to person.

What Are the Side Effects of Opsumit?

This is not a complete list of side effects, and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your healthcare provider or a pharmacist. You may report side effects to the FDA at www.fda.gov/medwatch or 800-FDA-1088.

Common Side Effects

The most common side effects of Opsumit are:

  • Cold-like symptoms (e.g., fever, chills, body aches)
  • Stuffy or runny nose
  • Sore throat
  • Headache
  • Urinary tract infection (UTI)
  • Low red blood cells (anemia)

Severe Side Effects

Opsumit can cause serious fetal harm if given to a pregnant person. Do not take it if you are pregnant or planning to become pregnant. Additionally, call your healthcare provider immediately if you are experiencing any of following:

  • Burning pain when you urinate
  • Feeling tired or weak, which may be caused by anemia
  • Liver problems, with signs like upper stomach pain or itching, persistent loss of appetite, dark-colored urine, yellowing of the skin or eyes (jaundice), and changes to your liver function test
  • Swelling of arms, hands, ankles, or feet (fluid buildup, rapid weight gain), with fluid buildup possibly causing or worsening heart failure
  • Worsening of or new heart problems (e.g., chest pain or irregular heartbeat)
  • Worsening of or new lung problems (e.g., shortness of breath, wheezing, or gasping)
  • Severe allergic reaction, with a rash, hives, wheezing, trouble breathing, or swelling of the mouth, face, lips, tongue, or throat

Long-Term Side Effects

Opsumit is generally well-tolerated. However, although rare, some serious long-term side effects can occur, including:

  • Liver damage: Your healthcare provider will check your liver function regularly during treatment. 
  • Heart problems: Tell your healthcare provider immediately if you see unusual swelling in hands, arms, feet, or legs, or rapid weight gain (more than 3 pounds in a day or 5 pounds in a week).
  • Lung problems: Tell your healthcare provider immediately if you experience shortness of breath, wheezing, or gasping.
  • Reduced sperm count in men: Tell your healthcare provider if fertility is a concern for you.

Report Side Effects

Opsumit may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your healthcare provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much Opsumit Should I Take?

Drug Content Provided and Reviewed by IBM Micromedex®

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For oral dosage form (tablets):
    • For pulmonary arterial hypertension:
      • Adults—10 milligrams (mg) once a day.
      • Children—Use and dose must be determined by your doctor.


The following treatment modifications should be kept in mind when using Opsumit:

  • If you have liver or kidney problems, ask your healthcare provider before you stop or start the medication.
  • If you are over 65 years of age, talk to your healthcare provider and discuss if any dose adjustment is needed for you. 
  • There is limited information proving its safety and effectiveness in children.
  • Do not take Opsumit if you are pregnant due to the potential for serious fetal harm. 
  • Do not breastfeed if you are taking Opsumit.

Missed Dose

If you miss a dose of Opsumit, take it as soon as you remember. Take the next dose at your regular time. If you are close to the time you would take your next dose, skip the missed dose. Take the next scheduled dose at your regular time.

Overdose: What Happens If I Take Too Much Opsumit?

Single doses as high as 600 milligrams have been given to otherwise healthy people. These individuals experienced side effects such as headache, nausea, and vomiting.

Call your healthcare provider immediately if you've taken too much of your medication.

What Happens If I Overdose on Opsumit?

If you think you or someone else may have overdosed on Opsumit, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking Opsumit, call 911 immediately.


Drug Content Provided and Reviewed by IBM Micromedex®

It is very important that your doctor check your progress at regular visits to make sure this medicine is working properly and to check for unwanted effects. Blood tests may be needed to check for unwanted effects.

Using this medicine while you are pregnant can cause very serious birth defects. Use 2 forms of effective birth control to keep from getting pregnant while you are using this medicine (even if the medicine is temporarily stopped), and for at least 1 month after you stop taking the medicine. The most effective forms of birth control are hormone birth control pills, patches, shots, vaginal rings, or implants, or a vasectomy (for men). One of these forms of birth control should be combined with a condom, a diaphragm, or a cervical cap. If a woman has had a tubal ligation or has an IUD, she does not need to use a second form of birth control. If you think you have become pregnant while using this medicine, tell your doctor right away.

If you are a woman who can get pregnant, you must have a negative pregnancy test before you will be allowed to take this medicine. You will also be required to have a pregnancy test every month during your treatment. If you miss a period while you are using this medicine, tell your doctor right away.

Check with your doctor right away if you start to have nausea, vomiting, fever, dark-colored urine or pale stools, a loss of appetite, pain in your upper stomach, or yellow eyes or skin. These could be signs of liver injury.

This medicine may cause fluid retention in some patients. Tell your doctor right away if you have bloating or swelling of the face, arms, hands, lower legs, or feet, or rapid weight gain after using this medicine.

Pulmonary edema may occur with this medicine. Check with your doctor right away if you have chest pain, difficult, fast, or noisy breathing, blue lips and fingernails, pale skin, increased sweating, coughing that sometimes produces a pink frothy sputum, or trouble breathing.

This medicine may decrease the amount of sperm men make and affect their ability to have children. If you plan to have children, talk with your doctor before using this medicine.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

What Are Reasons I Shouldn’t Take Opsumit?

You should not take Opsumit:

  • If you are pregnant, planning to become pregnant, or unable to use two forms of birth control
  • If you have a serious allergic reaction (such as rash or difficulty breathing) to any of the ingredients in Opsumit
  • If you are taking certain medications (such as ketoconazole, fluconazole, ritonavir, amiodarone, or rifampin) that may potentially change the breakdown of Opsumit, consult your healthcare provider for more information.

What Other Medications Interact With Opsumit?

Before starting Opsumit, tell your healthcare provider about all the medications you are taking, including prescription or over-the-counter (OTC) medications, vitamins, and herbal products.

Once absorbed into your body, Opsumit is broken down by a group of proteins, or enzymes. This process is known as drug metabolism. Other drugs may affect how these proteins act in your body and change the metabolism of Opsumit.

The following drugs may decrease the breakdown of Opsumit in your body. As a result, the effects of the medication may be increased. These medications include:

Additionally, the breakdown activity can be increased by certain medications and substances listed below. As a result, the effects of the medication may be reduced. These include:

This list does not contain all possible drug interactions with Opsumit. Your healthcare provider may change your prescription after carefully weighing the risks and benefits. 

What Medications Are Similar?

Other medications that belong to the same drug class as Opsumit include:

  • Tracleer (bosentan)
  • Letairis (ambrisentan)

Other examples of medications for the treatment of pulmonary hypertension include:

  • Phosphodiesterase inhibitors (PDE5I) such as Adcirca (tadalafil) and Revatio (sildenafil) 
  • Guanylate cyclase stimulant such as Adempas (riociguat)
  • Prostacyclin receptor agonists such as Uptravi (selexipag)
  • Prostanoids such as Flolan or Veletri (epoprostenol), treprostinil, and Ventavis (iloprost)
  • Calcium channel blockers (CCBs) such as Cardizem (diltiazem), nifedipine, and Norvasc (amlodipine)

The above list contains drugs used for high blood pressure in the lungs. It is not a list of drugs recommended to take with Opsumit. This list does not contain all the medications that can be used for this condition.

Frequently Asked Questions

  • What is the REMS program for Opsumit?

    Opsumit and other medications in the same drug class can cause serious birth defects. Therefore, this type of drug is only available under a special program called Risk Evaluation and Mitigation Strategy (REMS). You must be registered in the program and understand the risks and benefits of taking this medication. If you are female, you must provide a negative pregnancy test before starting the medicine. It is also necessary to use two forms of acceptable birth control while taking Opsumit and for one month after the last dose. You will need to provide a negative pregnancy test every month before you can get a refill from your pharmacy.

  • Is there a generic for Opsumit?

    Opsumit is not available in a generic form. However, Tracleer and Letairis, which are part of the same drug class as Opsumit, have generics available.

  • Where can I get Opsumit?

    Opsumit is a specialty medication. You cannot fill this at a regular pharmacy. You may pick up the medication at a specialty pharmacy, or the specialty pharmacy may mail the medications to you if you meet their criteria. 

  • Is there a way to help me save on Opsumit?

    Since there is no lower-cost generic available, Opsumit may be expensive for some. If cost is a concern for you, ask your healthcare provider or pharmacist if you are eligible for a prescription assistance program.

  • Can I take Opsumit with sildenafil or tadalafil?

    Your healthcare provider may prescribe one of the phosphodiesterase inhibitors (PDE5I), such as tadalafil or sildenafil, along with Opsumit. These medications help relax the blood vessels in your lungs through different methods.

How Can I Stay Healthy While Taking Opsumit?

Take your medication exactly as prescribed by your healthcare provider. Do not stop or change your regimen without medical guidance.

Opsumit carries serious safety warnings, such as the potential for fetal harm if used during pregnancy. If you are a female of reproductive potential, talk to your healthcare provider about the requirements for using Opsumit. For example, you will be asked to take regular pregnancy tests and use two reliable forms of contraception to be safe.

Your healthcare provider will also check your liver function and red blood cell levels regularly. 

Make sure to get all appropriate vaccinations, such as for flu and pneumococcal pneumonia, to prevent infections that can worsen PAH. While taking this medication regularly, it is also important to get lots of rest, stay well hydrated, and eat a healthy diet as instructed by your healthcare provider.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended to replace medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

The author would like to recognize and thank Yufeng Zhai for contributing to this article.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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