8 Opsumit Side Effects and How to Manage Them

Pulmonary arterial hypertension (PAH) is a health condition characterized by high blood pressure in the lungs caused by thickened, narrow arteries. It’s a progressive condition, meaning that it gets worse over time. But some medications, such as Opsumit (macitentan), can help slow this down.

If you’ve been prescribed Opsumit, it’s a good idea to familiarize yourself with its potential side effects. The common cold and headaches are a few examples. But in rare cases, serious Opsumit side effects are also possible. Here’s what you should know.

Opsumit side effects at a glance

Not everyone who takes Opsumit will have side effects. But people reported several side effects from it during clinical studies. 

Common Opsumit side effects (reported by over 5% of people) include:

• Common cold

• Anemia (low red blood cell count)

• Bronchitis

• Headache

• Urinary tract infection 

• Influenza

More serious side effects that are possible from taking Opsumit include:

• Liver damage

• Swelling

• Decreased sperm counts

• Harm to a growing fetus

Below, we’ll review eight of these side effects in more detail. Keep in mind that other side effects may be possible.

1. Common cold and other infections

It’s normal for adults to experience multiple colds each year. It isn’t clear why, but researchers found that more people who took Opsumit reported having a cold in clinical studies. This was compared to those who took a placebo (no active medication).

If you do catch a cold, there are several things you can do to ease your symptoms. Many medications at your local pharmacy can help with cough, congestion, and runny nose. But avoid products that can worsen PAH symptoms, such as decongestants like pseudoephedrine (Sudafed). Be sure to drink plenty of fluids and get rest. Gargling salt water can soothe a sore throat and loosen up mucus.

More people taking Opsumit also got influenza and urinary tract infections compared to those taking a placebo. If you think you have an infection, contact your primary care provider.

2. Headache

Another common Opsumit side effect is headache. In clinical studies, 14% of people taking Opsumit reported getting a headache during treatment. However, Opsumit is often taken with medications such as sildenafil (Revatio) or tadalafil (Adcirca). These medications are well-known for causing headaches. 

You can manage headaches at home most of the time. Reducing stress and drinking enough fluids can help ease symptoms. Getting enough sleep is also important. You can also try a pain reliever, such as acetaminophen (Tylenol). But if your symptoms are bothersome, contact your healthcare team for advice.

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• How they compare: Many medications can help manage pulmonary arterial hypertension (PAH). Learn about the different types of PAH medications and how they stack up against one another.

• Guide to pulmonary arterial hypertension: Experts break down the different symptoms, causes, and treatments of PAH.

• Portable oxygen therapy: Oxygen therapy can help with PAH symptoms such as shortness of breath. Learn more about portable oxygen options that allow you to use oxygen outside the home.

3. Anemia

Anemia, or a low red blood cell count, is another possible Opsumit side effect. It’s not known how Opsumit causes red blood cells to drop. Before starting Opsumit, your prescriber will order blood tests to check your blood cell counts.

Symptoms of anemia include:

• Feeling weak or more tired than usual

• Fast heartbeat

• Dizziness

• Pale skin

• Shortness of breath

• Chest pain

For most people, the drop in red blood cell counts happens soon after starting Opsumit. It usually becomes stable after a while. Typically, no treatment is needed. But if your red blood cell count gets too low, your prescriber may need to stop the medication. After you stop taking Opsumit, your red blood cell count should get back to normal.

4. Bronchitis

In studies of Opsumit, about 12% of people reported bronchitis as a side effect. Although having bronchitis can be unpleasant, you can usually manage it at home. Try running a humidifier to soothe inflamed airways. Stay hydrated, rest, and ask your pharmacist about over-the-counter remedies to help you feel better.

If your bronchitis symptoms get worse or you have trouble breathing, blood in your mucus, or a fever, get medical attention right away.

5. Liver damage

Some people who took Opsumit during clinical studies had elevated liver enzymes. This can be a sign of liver inflammation or damage. Medications in the same drug class as Opsumit have been linked to liver injury. But severe liver problems from Opsumit don’t seem to be common.

Your prescriber will order a blood test to check your liver health before starting Opsumit. Tell them if you notice any symptoms of liver damage, such as vomiting, stomach pain, or dark urine. You may also notice your skin or the whites of your eyes turning a yellow color (jaundice). 

6. Swelling

Fluid retention and swelling in the arms and legs are common issues in people with PAH. And swelling tends to get worse as your condition progresses, especially if heart failure develops. But swelling is also a known side effect of medications like Opsumit. However, this may be less likely with Opsumit compared to other medications in its class.

If you notice a sudden increase in your weight or swelling in your ankles or legs, contact your prescriber. They may give you medication to treat your symptoms or recommend putting your legs up or wearing compression socks. They may also tell you to restrict the amount of fluids or sodium (salt) that you consume each day.

7. Decreased sperm counts

There are many reasons for having a low sperm count. And taking Opsumit might be one of them. The manufacturer includes a warning about low sperm count based on studies of similar medications. But in some animal studies, Opsumit didn’t affect sperm count or the ability to have children. More research is needed in this area.

If you're looking to father a child, talk to your prescriber about whether Opsumit is the best choice for you.

8. Harm to a growing fetus

In animal studies, Opsumit caused harm to growing fetuses. This included birth defects and death. Because of these risks, you’ll be enrolled in a mandatory risk management program while taking Opsumit if you’re able to get pregnant.

As part of the program, you’ll take a pregnancy test before starting Opsumit and monthly thereafter. A final pregnancy test is required one month after stopping the medication. You’ll also need to use effective birth control during this time.

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Written by:

Kristianne Hannemann, PharmD

Kristianne Hannemann, PharmD, is a licensed pharmacist in California. She has been a retail pharmacy manager and staff pharmacist for over 7 years and has contributed drug information content to different health companies.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Austin Ulrich, PharmD, BCACP

​​Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. Ulrich’s experience includes direct patient care in hospital and community pharmacies.

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