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-P and Lomaira.

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.”

You might also be concerned about headaches from phentermine and other possible side effects. Continue reading to learn more about phentermine, its common side effects, 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 so that 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. Someone with obesity has 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, which is sold under the brand name Qsymia. 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’s the Connection Between Phentermine and Pulmonary Hypertension?

People who took phentermine combined with fenfluramine (fen-phen) or dexfenfluramine — appetite suppressants popular in the ’90s — were found to have developed pulmonary arterial hypertension (PAH). This subtype of PH is caused by the 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 that fenfluramine and dexfenfluramine be taken off the market in 1997. 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 — that is, causing PH as long as 10 years after use!”

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

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.

Does Phentermine Cause Headaches?

Headaches are one of the known side effects of phentermine. Phentermine works by stimulating the central nervous system (CNS), in a way that is similar to the effect of amphetamines. It can trigger the release of the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones control your fight-or-flight response, which is typically a response to stress. Stress, adrenaline, and headaches are all connected.

Adrenaline increases your heart rate and redirects blood to areas like your muscles, which are more useful when you’re stressed or in danger. This can result in changes in blood flow, which can contribute to headaches and migraines.

What Are the Other Side Effects of Phentermine?

Like most medications, phentermine comes with some side effects. In addition to headaches, side effects of phentermine include:

• 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:

• Trouble with 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?

For people with PH, it’s important to know which phentermine side effects specifically affect your heart, including:

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

Combining phentermine and topiramate can speed up your heart rate by as much as 20 beats per minute when you’re not being physically active. 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 PH.

How To Get Rid of a Phentermine Headache

Talk to your doctor about how to get rid of phentermine headaches if you experience them often. They may recommend:

• Resting
• Staying hydrated
• Applying a hot or cold compress
• Using over-the-counter painkillers such as ibuprofen (Motrin)

Always consult your health care provider before using medications to manage headaches from phentermine.

How To Avoid Headaches and Other Side Effects on Phentermine

To avoid headaches on phentermine, be sure to follow all instructions from your doctor. Only take the medication for as long as your health care provider has prescribed it. Your side effects may go away as your body adjusts to 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 (SSRIs) — 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 taking 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.

Talk With Others Who Understand

On myPHteam, the social network for people with pulmonary hypertension and their loved ones, more than 56,000 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 have headaches or any other side effects? Share your experience in the comments below, or start a conversation by posting on your Activities page.