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What Are the Most Common Side Effects of Phentermine?

By Madeleine A.
Updated Mar 03, 2024
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Common side effects of phentermine include high blood pressure, heart palpitations, and anxiety. In addition, side effects of this medication can include dizziness, trouble sleeping, and headache. Phentermine is a drug used as an appetite suppressant in the treatment of weight loss. This medication should only be used when obesity has the potential to lead to health problems, and only under the strict supervision of a health care professional.

Other side effects include euphoria, tremors, and restlessness. People with high blood pressure or cardiovascular disease should not take phentermine unless deemed safe by their physicians. In addition, it may not be safe to take phentermine when taking prescription medications because the combination can be harmful. This is especially true when taking medications such as beta blockers or other cardiovascular medications.

Constipation, diarrhea, and dry mouth are other side effects of phentermine. In addition, an unpleasant or metallic taste in the mouth can also occur. Also, depression can sometimes occur as a result of central nervous system alterations. Changes in libido and impotence may also occur, although these symptoms are usually not permanent.

If side effects occur when taking phentermine, people should immediately stop taking the drug and call their physicians. Side effects of phentermine that are considered very serious include difficulty breathing, shortness of breath, and chest pain. In addition, feeling faint and seizures are serious side effects that may require emergency medical evaluation and treatment. Those who have psychiatric conditions may not be candidates for phentermine because this medication can provoke intense nervousness.

An addiction to phentermine can also develop because it can be habit forming, and those who have a history of drug abuse or problems with alcohol should talk with their doctors to determine if they can take phentermine safely. In addition, women are trying to get pregnant, who are already pregnant, or who are breast feeding a baby should also avoid taking phentermine. The medication may also get into breast milk and cause serious side effects to the baby.

Many health care providers recommend alternatives to medications for their patients who are trying to lose weight. Alternatives include eating a healthy diet high in fruits and vegetables, consuming plenty of fiber, and exercising. In addition, drinking water throughout the day can help increase the metabolism and flush out toxins. Maintaining a healthy weight is important to optimal health and can even help reduce the risk of high blood pressure, heart disease and diabetes.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
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Discussion Comments
By candyquilt — On Jul 05, 2013

@feruze-- Lisinopril is a high blood pressure medication right? I had heard that lisinopril and phentermine are sometimes given together obesity causes blood pressure to go up.

I think your situation is different because you're taking two drugs together. You might have additional side effects from their interaction.

By stoneMason — On Jul 04, 2013

@feruze-- Dizziness and diarrhea are very common side effects of phentermine. I had dizziness, dry mouth and nausea when I first started taking it as well. It did get better after a few weeks. I still have dry mouth, but it's tolerable.

It usually takes several weeks for our bodies to adjust to new medications. I think things will get better for you. If the side effects don't lessen though and if you also start getting migraines and heart palpitations, you need to tell your doctor.

My doctor said that nausea and dizziness are nothing to worry about but if I start experiencing heart palpitations, he said he would reduce my dose.

By bear78 — On Jul 04, 2013

I started taking phentermine last week (in addition to lisinopril) and I've been dizzy every single day. I'm also experiencing some diarrhea.

Will these side effects go away with time, or is it always going to be like this? I'm quite miserable right now.

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