A link may exist between phentermine and heart failure. There are rare reports of valvular heart disease in people who have taken phentermine, and it may also cause pulmonary hypertension.

Valvular heart disease involves damage to one or more of the valves in the heart. These valves open and close to regulate blood flow.

Additionally, phentermine may cause another, equally serious, side effect: pulmonary hypertension. This is high blood pressure in the arteries of the lungs.

People with cardiovascular disease or conditions affecting the heart and lungs should not take phentermine.

This article discusses the association between phentermine and heart failure. It also examines who should not take the drug, other risks, and alternative help for obesity.

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Phentermine is a brain and spinal cord stimulant medication. It can suppress a person’s appetite, making it popular as a weight loss drug.

In 1959, phentermine first came onto the market as part of a combination obesity drug. Then, in the 1980s, researchers discovered that phentermine and fenfluramine — another appetite suppressant — had a synergistic effect when a person took them together.

This means their combined effect was greater than the sum of their two separate effects. At this time, the combination drug “fen-phen” became a mainstay of obesity treatment.

However, fen-phen had a strong link to pulmonary hypertension and valvular heart disease. Researchers also discovered a link between fenfluramine alone and these two conditions.

Consequently, the Food and Drug Administration (FDA) banned fenfluramine in 1997, but it continues to allow the short-term use of phentermine.

Sometimes, doctors prescribe phentermine alone. Alternatively, they prescribe a combination drug containing topiramate, an antiseizure drug. The possibility of heart failure differs when taking phentermine alone and taking the combination drug.


Experts cannot rule out a link between phentermine alone and heart valve disease. There have been rare reports of the condition manifesting in people who took it.

Combination of phentermine and topiramate

The combination of phentermine and topiramate may increase resting heart rate up to 20 beats per minute (bpm). This means that a person who normally has a resting heart rate of 75 bpm would have a resting heart rate as high as 95 bpm.

Despite this adverse effect, the product label does not mention a risk of heart valve disease, as in phentermine alone.

Additionally, the combination of phentermine and topiramate can cause serious interactions with other medications that can affect the heart. For example, when a person takes it with a selective serotonin reuptake inhibitor (SSRI) medication, it may cause serotonin syndrome. This can be very dangerous.

People with cardiovascular disease have a higher risk of heart side effects, so they should not take phentermine. This includes those with:

Researchers cannot rule out an association between phentermine alone and pulmonary hypertension, a rare but often fatal condition. A person should stop taking phentermine if they develop symptoms such as difficulty breathing, chest pain, fainting, or swelling of the legs.

Other than the possibility of pulmonary hypertension and valvular heart disease, phentermine has the following health risks:

  • It can impair the ability to engage in hazardous activities: A person may not be able to safely operate machinery or drive a motor vehicle.
  • A person can develop a tolerance: This means an individual may require a larger dose to receive the same effect. It is unsafe to exceed the recommended dosage.
  • It can lead to abuse and dependence: Since phentermine is chemically related to amphetamine, it poses these dangers.
  • It negatively interacts with alcohol: Individuals should not consume alcoholic beverages when taking phentermine.
  • It negatively interacts with certain drugs: People should not take other weight loss products or SSRIs when taking phentermine.

Although the FDA has approved phentermine for short-term use, more clinical trials regarding its long-term safety to use it for 6 months or longer are necessary, notes an older 2014 study. Research on the cardiovascular effects after more than 1 year’s use is especially scarce.

Below are some possible phentermine alternatives.


Acupuncture is an alternative treatment that involves inserting thin needles onto pressure points of the body.

A 2018 review evaluated 21 studies involving 1,389 participants on the value of acupuncture for obesity. The authors concluded that it was a safe and effective treatment, but more long-term research is necessary.

Mediterranean diet

Doctors do not advise going on fad diets to lose weight because they are often unhealthy and unsustainable. However, nutritious and balanced eating plans such as the Mediterranean diet can yield long-term, maintainable weight loss.

The diet includes nutrient-rich, high-fiber foods, such as fruits, vegetables, nuts, and whole grains. It also includes olive oil and fatty fish.

Older research from 2010 assessed the efficacy of the Mediterranean diet in preventing obesity in 10,376 participants. The authors concluded that it could slow age-related weight gain. Because the diet has high palatability, it has a high potential for adherence.

Other anti-obesity medications

Aside from phentermine, there are other anti-obesity medications available. These include:

  • orlistat (Xenical), which reduces fat absorption
  • naltrexone-bupropion (Contrave), which decreases appetite or promotes a feeling of fullness
  • liraglutide (Saxenda) or semaglutide (Wegovy), which mimics a hormone that may regulate appetite
  • setmelanotide (Mcivree), which may decrease appetite, boost the feeling of fullness, and increase metabolism

However, it is important to note that all of the above have side effects and risks, some of which can be serious. If a person’s doctor thinks they should take an anti-obesity medication, they will prescribe the appropriate medication and dose.

Weight loss surgery

Weight loss surgery may be an option for people with a body mass index of 35 or higher. It promotes weight loss by making changes in a person’s digestive system. One common type, bariatric surgery, works by dividing the stomach to make a smaller upper pouch.

The options have short-term side effects and long-term risks. However, when other weight loss medications and diets have not produced adequate results, doctors may consider surgery. A person needs to stick to a sustainable diet and exercise plan to maintain results.

The possible link between phentermine and heart failure stems from rare reports of valvular heart disease in people who took the drug. The medication also may cause pulmonary hypertension, which can be fatal.

Sometimes, instead of prescribing phentermine alone, doctors prescribe a medication that combines phentermine with topiramate. This combination can increase heart rate.

If a person has any type of cardiovascular disease, they should not take phentermine. Also, before someone takes phentermine, they should disclose to their doctor the other medications and supplements they take to be sure there is no potential for harmful interactions.