Letairis (Ambrisentan) – Oral


Letairis carries a boxed warning from the Food and Drug Administration (FDA). This warning states that Letairis should not be taken during pregnancy due to the risk of fetal harm. Because of this risk, prescribers must enroll their female patients (referring to sex assigned at birth) in a special program called the Ambrisentan Risk Evaluation and Mitigation Strategy (REMS).

What Is Letairis?

Letairis (ambrisentan) is a prescription medication used to treat adults with pulmonary arterial hypertension (PAH), or high blood pressure in the pulmonary artery. It belongs to a class of drugs called endothelin receptor antagonists.

People with PAH have high levels of endothelin, a naturally occurring substance that causes the pulmonary artery to become too narrow, which leads to increased pressure. Letairis works by blocking the effects of endothelin to help prevent narrowing of the blood vessels. This action decreases the pressure within this blood vessel, making it easier for people with PAH to exercise.

You will likely need to use a specialty pharmacy to receive Letairis as only certified pharmacies can dispense the medication. Letairis comes as a tablet that you swallow.

Drug Facts

Generic Name: Ambrisentan

Brand Name(s): Letairis

Administration Route(s): Oral

Drug Availability: Prescription

Therapeutic Classification: Antihypertensive agent

Available Generically: Yes

Controlled Substance: N/A

Active Ingredient: Ambrisentan

Dosage Form(s): Tablet

What Is Letairis Used For?

The Food and Drug Administration (FDA) approved Letairis to treat adults with PAH. Specifically, Letairis is indicated to improve their ability to exercise and to slow the worsening of PAH symptoms. People with this condition have frequent shortness of breath, dizziness, and chest pain, especially during physical activity.

Letairis is also FDA approved for use in combination with another medication, tadalafil (common brands include Adcirca and Alyq), to reduce the risk of symptom worsening and hospitalization in adults with PAH and improve their ability to exercise.

Letairis (Ambrisentan) Drug Information - Illustration by Zoe Hansen

Verywell / Zoe Hansen

How to Take Letairis

Take Letairis by mouth as directed by your healthcare provider. The typical dosing for Letairis is once daily. It doesn’t matter what time of day, but it’s best to take Letairis around the same time each day. You may take Letairis with or without food.  

Letairis comes as a tablet that you swallow whole. Do not crush, split, or chew Letairis tablets.

Letairis carries a boxed warning from the FDA. This warning states that Letairis should not be taken during pregnancy because it can cause harm to the fetus. Because of this risk, your healthcare provider may require you in a special program called the Ambrisentan Risk Evaluation and Mitigation Strategy (REMS).

Do not use Letairis if you are pregnant or think you might be pregnant as this medication can cause serious birth defects. The REMS program requires females (sex assigned at birth) who can become pregnant and use Letairis to take a pregnancy test to confirm they are not pregnant before starting this medication.

Pregnancy tests are repeated monthly during treatment and one month after treatment ends. Birth control should also be used during treatment and for one month after stopping the last dose.


Store Letairis in its original container at room temperature, away from excess heat and moisture (not in a bathroom). It should be tightly closed and out of reach of children.

Off-Label Uses

Letairis is FDA approved for use in adults with PAH. But some healthcare providers may choose to prescribe Letairis “off-label” to children with pulmonary hypertension. Since the drug is only FDA approved for adults, pediatric use is considered off-label.

A healthcare provider may prescribe off-label treatments when the decision is supported by scientific evidence or expert clinical experience. Guidelines from the American Heart Association and American Thoracic Society include ambrisentan as a treatment option for children with pulmonary hypertension.

How Long Does Letairis Take to Work?

Letairis starts working soon after you take your first dose. It typically takes at least four weeks for people to notice an improvement in their ability to exercise.

What Are the Side Effects of Letairis?  

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

Common Side Effects

The following side effects are common while taking Letairis:

  • Swelling due to edema (fluid buildup) in your legs, feet, ankles, or hands
  • Stuffy nose
  • Sinusitis
  • Flushing (your face temporarily reddens and feels hot)

When used in combination with tadalafil, Letairis can cause additional common side effects including:

Severe Side Effects

Less commonly, serious side effects can occur while taking Letairis. If you notice the symptoms described below, call your healthcare provider right away. Call 911 for emergency medical care if your symptoms feel life-threatening. Severe side effects and their symptoms can include the following:

  • Edema (fluid buildup) all over your body: Swelling, rapid weight gain, fatigue, trouble breathing
  • Liver problems: Nausea, vomiting, pain in your upper right abdomen, yellowing of your skin or eyes, dark urine, itchiness

Long-Term Side Effects   

Letairis may cause side effects that continue to affect you even after treatment. The following long-term side effects have been reported after treatment with Letairis:

  • Risk of birth defects: Letairis may cause fetal harm, including serious birth defects. If you can become pregnant, it is very important to follow your prescriber’s instructions. Taking this medication requires regular pregnancy testing and two reliable methods of effective birth control use.
  • Low sperm count: Letairis may cause decreased sperm count. If you are male (sex assigned at birth), this may affect your fertility. Before starting Letairis, it is important to talk to your provider about whether you wish to have biological children in the future. They can give you more information about family planning options, such as banking your sperm.

Report Side Effects

Letairis 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 provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

  Dosage: How Much Letairis 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—At first, 5 milligrams (mg) once a day. Your doctor may increase your dose to 10 mg once a day, as needed.
      • Children—Use and dose must be determined by your doctor.

Missed Dose

If you miss a dose of Letairis, take it as soon as you remember that day. Then take your next dose at your usual time. You should not take two doses at the same time to make up for a missed dose.

Overdose: What Happens If I Take Too Much Letairis?

Overdose symptoms may include:

  • Headache
  • Flushing
  • Dizziness
  • Nausea
  • Nasal congestion
  • Hypotension (low blood pressure)

What Happens If I Overdose on Letairis?

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

If someone collapses or isn't breathing after using Letairis, 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. Blood tests may be needed to check for unwanted effects.

Using this medicine while you are pregnant can cause very serious birth defects. Use a highly effective birth control or 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 your last dose. 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 partner’s vasectomy is the chosen method of contraception, a hormone or barrier method must be used along with this method. 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 and for 1 month after treatment with this medicine. If you miss a period while you are using this medicine, tell your doctor right away.

This medicine may cause fluid retention (edema) in some patients. Check with your doctor right away if you are gaining weight rapidly, have swelling in your hands, ankles, feet, or all over the body, or if you have trouble breathing while you are using this medicine.

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

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

Pulmonary edema (swelling in the lungs) 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, or coughing that sometimes produces a pink frothy sputum.

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 Letairis?

Letairis may not be safe for everyone. You should not take Letairis if:

  • You are pregnant or breastfeeding.
  • You have a lung disease called idiopathic pulmonary fibrosis.
  • You have liver disease.
  • You had an allergic reaction to Letairis or any of its ingredients in the past.

What Other Medications Interact With Letairis?

Drug interactions occur when one drug affects how another drug works. Some drug interactions may be safely avoided or managed by dose adjustments by your healthcare provider.

When ambrisentan (the active ingredient in Letairis) was tested for drug interactions, only one interaction was noted as significant: cyclosporine, which is available under the brand names Gengraf, Neoral, and Sandimmune. Cyclosporine is an immunosuppressant drug. If you take this medication, your provider will most likely give you a lower dose of Letairis.

Other drug interactions are possible. Before taking Letairis, talk to your provider about all of your current medications, including prescription drugs, over-the-counter medicines, vitamins, herbs, and other dietary supplements.

What Medications Are Similar?

Letairis belongs to a class of drugs called endothelin receptor antagonists. Other endothelin receptor antagonist drugs that are similar to Letairis include:

  • Tracleer (bosentan) 
  • Opsumit (macitentan)

In some cases, healthcare providers prescribe an endothelin receptor antagonist drug along with other types of drugs to treat PAH, such as:

  • Adcirca and Alyq (tadalafil) 
  • Revato (sildenafil)

If you have questions about other treatment options for PAH, talk to your healthcare provider.

Frequently Asked Questions

  • Should I expect any side effects after starting Letairis?

    Specific side effects of Letairis occur more commonly during the first few weeks of treatment. These include anemia (low red blood cells) and edema (fluid buildup). With anemia, you might feel more tired or look more pale than usual. With edema, you may have swelling or puffiness all over your body, especially in your hands, ankles, lower legs, and feet.

    These side effects usually go away with the continued use of Letairis. Be sure to tell your healthcare provider if you experience symptoms of anemia or edema. They may prescribe treatments to manage these side effects, such as iron supplements for anemia or “water pills” (diuretics) for edema.

  • How does Letairis work?

    Letairis belongs to a class of drugs called endothelin receptor antagonists. Letairis works by blocking the effects of a natural substance called endothelin that causes narrowing of the pulmonary artery. This narrowing leads to high blood pressure in the blood vessels in the lungs.

    People with PAH have high levels of endothelin. Blocking the action of endothelin can help reduce the pressure, which helps to improve PAH symptoms.

  • Can I take tadalafil at the same time as Letairis?

    Yes. Letairis is commonly prescribed along with tadalafil (brands include Adcirca and Alyq). If your healthcare provider prescribes both Letairis and tadalafil, you can take them at the same time each day.

  • How long does it take for Letairis to work?

    It may take anywhere from one to three months of taking Letairis to notice an improvement. During this time, your healthcare provider may adjust your dosage until they find the correct dose for you.

  • How can I tell that Letairis is working for me?

    Letairis can help reduce the symptoms of pulmonary arterial hypertension (PAH). Common PAH symptoms include shortness of breath, dizziness, and chest pain, especially during physical activity. Once the drug is working, it should be easier for you to breathe and exercise.

How Can I Stay Healthy While Taking Letairis?

Living with PAH can be challenging. But medications such as Letairis may reduce your symptoms and improve your ability to exercise. Regular exercise, to the best of your ability, helps to maintain muscle strength and fitness. Staying fit can help you continue doing your daily activities for as long as possible.

Medical Disclaimer

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

3 Sources
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.
  1. Food and Drug Administration. Letairis (ambrisentan) tablets, for oral use.

  2. National Organization for Rare Disorders. Pulmonary arterial hypertension.

  3. Abman SH, Hansmann G, Archer SL, et al. Pediatric pulmonary hypertension: guidelines from the American Heart Association and American Thoracic Society. Circulation. 2015;132(21):2037-2099. doi:10.1161/CIR.0000000000000329

By Patricia Weiser, PharmD
Patricia Weiser, PharmD, is a licensed pharmacist and freelance medical writer. She has more than 14 years of professional experience.