If you’re trying to lose weight, your doctor may prescribe a weight loss drug called phentermine to boost your efforts. Phentermine is sold under several brand names, such as Adipex, Adipex-P, and Fastin.

Your doctor may have suggested losing weight to help prevent conditions like high blood pressure and coronary heart disease, which are associated with an increased risk of pulmonary hypertension (PH). However, you may have heard that phentermine is linked to developing PH. A myPHteam member who took phentermine commented, “The irony is, the use of a diet pill (phentermine) may have caused PH.”

Continue reading to learn more about phentermine and how it may be linked to pulmonary hypertension.

What Is Phentermine?

Phentermine belongs to a class of drugs called anorectics — it suppresses your appetite to help you eat less. This medication is prescribed to manage obesity and aid weight loss, as part of a plan that includes a reduced-calorie diet and exercise. Obesity is defined as a calculated body mass index (BMI) of 30 or higher. Some people who have a BMI of 27 may take phentermine if they have additional risk factors, such as high blood pressure, diabetes, or high cholesterol.

Phentermine may also be combined with another drug, topiramate, and sold under the brand name Qsymia. When taken alone, phentermine is available as a pill in forms that can be taken either once a day or 30 minutes before each meal. Phentermine plus topiramate is usually taken once daily, in the morning. These medications should be taken exactly as your doctor instructs.

To reduce the impact of side effects, phentermine is recommended only for short-term use — up to three months at a time.

What Are the Side Effects of Phentermine?

Like most medications, phentermine comes with some risks. Common side effects of phentermine include:

• Headache
• Dry mouth
• Dizziness
• Anxiety or excitability
• Diarrhea or constipation
• Difficulty sleeping
• Unpleasant taste in your mouth
• Low sex drive
• Restlessness

Phentermine can also cause serious side effects, such as:

• Impaired ability to complete complex tasks like driving a car or operating machinery
• Allergic reactions such as hives, rash, or trouble breathing
• Risk of drug abuse and dependence — Phentermine is chemically related to amphetamine, another drug that’s commonly abused and may be habit-forming.

Talk to a health care professional right away if you experience any side effects that cause concern or don’t get better.

How Does Phentermine Affect Your Heart?

Some of phentermine’s side effects specifically affect your heart, including:

• Palpitations (fast or fluttering heartbeat)
• Tachycardia (increased heart rate)
• Higher blood pressure

Taking the combination of phentermine and topiramate can speed up your heart rate by as much as 20 beats per minute while you’re at rest. An increased heart rate is associated with a higher risk of dying from cardiovascular (heart) disease.

If phentermine raises your blood pressure, you may have a higher risk of heart disease. Damage over time from high blood pressure can make you more likely to develop coronary artery disease or have a heart attack.

Additionally, phentermine is associated with valvular heart disease — when the valves that connect the chambers of the heart get damaged or diseased. A damaged heart valve makes it harder for your heart to pump enough blood throughout your body. This can set off a chain reaction that affects your lungs and pulmonary arteries, leading to pulmonary hypertension.

Can Phentermine Cause Pulmonary Hypertension?

People who took phentermine combined with fenfluramine (fen-phen) or dexfenfluramine (Redux) — appetite suppressants popular in the ’90s — were found to have developed pulmonary arterial hypertension (PAH) related to these medications. This subtype of PH is caused by narrowing of the pulmonary arteries, which carry blood from the heart to the lungs. PAH caused by using a medication is known as drug-induced PAH.

As a result, the U.S. Food and Drug Administration (FDA) recommended in 1997 that fenfluramine be taken off the market. Although PAH is associated with fenfluramine and dexfenfluramine, there have been reports of people developing the condition after taking phentermine alone. Some people were diagnosed with PAH years after they stopped using the medication.

A myPHteam member shared, “I totally fit the bill as far as the long-term effects from the phentermine — i.e., causing PH as long as 10 years after use!”

Phentermine’s drug labeling includes a warning about the link with valvular heart disease, like aortic or mitral valve disease. Valvular heart disease has also been reported in people taking phentermine plus fenfluramine and dexfenfluramine. Researchers don’t yet understand what role phentermine may play in developing valvular heart disease, which can cause PH.

The first symptom of PH is usually trouble breathing, such as feeling more out of breath when exercising. Talk to your doctor if you notice any new or bothersome side effects while taking phentermine.

What Other Drugs Are Linked to Pulmonary Hypertension?

Fenfluramine and phentermine aren’t the only drugs linked to PAH. Others include:

• Methamphetamine — A recreational drug
• Interferons — Proteins used to treat cancer, multiple sclerosis, and hepatitis C
• Dasatinib (Sprycel) — A leukemia treatment
• Mitomycin pyelocalyceal (Jelmyto) — A chemotherapy gel for treating cancer
• Selective serotonin reuptake inhibitors — A class of antidepressants

Talk to your doctor if you have specific concerns about any medications you currently take or have taken. Every medication carries risks, and your doctor can help you weigh the risks and benefits for your specific situation. Don’t stop a prescribed medication without seeking medical advice from your provider.

The FDA continues to monitor the side effects of approved drugs to protect public health. It’s important to report any new or unusual side effects you experience while taking any medication.

How Is Drug-Induced Pulmonary Arterial Hypertension Managed?

If you develop PAH while taking a medication, such as phentermine, your doctor will likely recommend you stop taking that drug. Your symptoms may then improve, although this isn’t always the case.

Your treatment for PAH depends on your symptoms. Treatment options include:

• Calcium channel blockers to lower blood pressure in your pulmonary arteries
• Diuretics (water pills) to help you get rid of extra fluid in your lungs
• Pulmonary vasodilators to relax your pulmonary arteries, improving blood flow and easing the strain on your heart
• Oxygen therapy, if needed, to raise a low level of oxygen in your blood

Be sure to talk with your doctor if you have concerns about any medications you take. They can guide you toward the best treatment plan to help you feel your best with the fewest side effects.

Talk With Others Who Understand

On myPHteam, the social network for people with pulmonary hypertension and their loved ones, more than 51,000 members come together to ask questions, give advice, and share their stories with others who understand life with PH.

Have you taken phentermine? Did you experience any side effects? Share your experience in the comments below, or start a conversation by posting on your Activities page.