Phentermine side effects you should know

Teresa Hong

Teresa Hong


Teresa Hong is a dietician who is actively engaged in food education. Develops nutritional methods available to as many people as possible. Offers specific dietary modification tools for people with endocrine disorders, food allergies, atherosclerosis, malnutrition, irritable bowel syndrome and other diseases. She will help to get rid of stress and enjoy every meal again!

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– Updated March 19, 2022

Do you want to lose weight quickly and effectively with Phentermine?  Are you concerned about the possible consequences it might have on your body? Let’s talk about the side effects of Phentermine. What can happen when taking a weight loss course, and what to do to avoid the adverse reactions?

Phentermine common side effects

Common side effects include:

  • Dry Mouth: A noticeably parched sensation in the mouth is one of Phentermine’s most common side effects.
  • Insomnia: Difficulties falling or staying asleep may occur as Phentermine can cause increased energy levels.
  • Increased Heart Rate: Patients may experience a faster-than-normal heart rate due to the drug’s stimulant properties.
  • Elevated Blood Pressure: A rise in blood pressure is possible, so regular monitoring is crucial during treatment.
  • Constipation: Some users report a noticeable change in bowel movements, often leaning towards constipation.

While these side effects are common, they are not exhaustive; only some patients experience them. Always consult a healthcare professional for a comprehensive understanding and management of potential side effects when using Phentermine.

Phentermine long-term side effects

Among the long-term adverse reactions of Phentermine there are the following:

digestive issues like nausea, vomiting, diarrhea, or constipation
dry mouth, an unpleasant lingering taste, and mucus in the throat
body rash
increased heart rate and blood pressure
decreased libido
CNS issues like hyperactivity, insomnia, irritability, and dizziness

Taking Phentermine and feeling hot is also a common side effect that passes quickly.

Since Phentermine causes the rapid release of the active substance, you need to pay attention to these symptoms and immediately report them to your doctor should they occur. Luckily, these symptoms appear in very rare cases.

Serious side effects of Phentermine may include:

pulmonary hypertension (high blood pressure in the lungs)
stenosis (poor functioning of the heart valve that can result in shortness of breath during a workout)
swelling and cramps
incoherent speech, confusion, and inability to concentrate

If you experience any of the listed side effects when taking Phentermine, inform your doctor immediately. 

If you have diabetes, consult your doctor first because you may need to reduce the dose of insulin. Do not take Phentermine if you are planning a pregnancy, are already pregnant, or are breastfeeding.

When it comes to the long-term side effects of Phentermine, prolonged use of the drug can result in physical and psychological dependence.

If you suddenly stop taking Phentermine, you may experience the following withdrawal symptoms:

excessive drowsiness
fatigue and withdrawal syndrome

How to avoid Phentermine side effects

Here are some basic guidelines that can help you avoid adverse effects:

1. Do not exceed the prescribed drug dosage under any circumstances.
2. Consistently monitor your well-being and if side effects occur, consult your doctor to reduce the dosage.
3. Do not drink alcohol and other stimulants.
4. Do not engage in excessive physical activity.
5. Balance out your meal plan.
6. Ask for support from like-minded people, as this will help you manage your psychological and emotional states.

This article uncovered the main Phentermine side effects that the drug can cause both on its own and when combined with alcohol during the treatment. Most of these side effects may disappear when your body gets used to the drug.

Besides that, your doctor can provide recommendations on preventing or minimizing some of these side effects. The important thing is to pay attention to how you feel and immediately contact your doctor if any serious symptoms occur!


While Phentermine is an effective weight loss medication, it’s essential to be aware of its potential side effects. These can range from common issues like dry mouth and insomnia to more severe effects such as heart-related complications. Individual experiences may vary, and certain side effects can be managed with proper care. However, it’s always crucial to discuss with your healthcare provider to weigh the benefits against potential risks before starting any medication regimen.


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