Phentermine Side Effects and Precautions

Phentermine is an appetite suppressant drug that has weight loss effect. This drug should be used properly to avoid the side effects associated to it. Familiar yourself with the phentermine side effects and the precautions in using the drug by reading this article.

Phentermine Overview

Phentermine is an FDA-approved appetite suppressant drug prescribed to obese patients who are at increased medical risk because of their weight. It should be used in short term (up to 12 weeks) and combined with diet, exercise, and behavioral modification. It comes in tablets and extended-release capsules. The drug is sold under different brand names such as Adipex-P, Ionamin, Obenix, Oby-Cap, Teramine, Zantryl, and among others.

How Does Phentermine Work?

Phentermine works by triggering the hypothalamus to release norepinephrin (a neurotransmitter) that signals a fight-or-flight response, reducing hunger. Besides from working at the hypothalasmus, phentermine also works outside the brain to trigger the release of epinephrine or adrenaline. This hormone causes fat cells to break down stored fat.

Precautions in Using Phentermine

There are certain precautions that you should know before and after taking phentermine. Knowing these precautions will protect you against the possible harm that the drug may cause.

  • Do not take phentermine if you are allergic to any of its ingredients. Ask for the ingredients of phentermine drugs to a pharmacist. Make sure to tell your doctor if you have any allergies.
  • Tell your doctor if you are taking or planning to take any prescription & non prescription medications, vitamins, herbal medicines, and nutritional supplements. There are medications that could possibly interact with phentermine and will cause harm to you. Examples are high blood pressure medications, insulin or diabetes medications, antidepressants, and among others.
  • Tell your doctor if you have or have ever had hypertension, heart disease, arteriosclerosis, hyperthyroidism, glaucoma, diabetes, or a history of drug abuse.
  • Tell your doctor if you are pregnant, planning to get pregnant, or breast-feeding. Call your doctor if you get pregnant while taking phentermine.
  • Do not drink alcohol because it adds to the drowsiness caused by taking phentermine. If you are drowsy after taking the drug, do not drive, use a machine, or do any work that requires alertness in order to avoid accidents.
  • Phentermine works best if it is accompanied by exercise and diet.
  • If you missed a dose, take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take extra dose to make up the missed one.
  • Read and follow the directions as written on your prescription label. Ask your doctor or pharmacist, if there is anything you can’t understand in the label. Do not take phentermine at a larger dose, take it more often, or for a longer period than your doctor tells you to.

Phentermine Side Effects

As with any drug, phentermine may cause side effects. However, there are some who can tolerate the side effects quite well.  In most cases, phentermine side effects occur when the drug is taken beyond what is prescribed.

The less serious phentermine side effects include dry mouth, vomiting, diarrhea, constipation, dry mouth, and unpleasant taste in the mouth. Tell your doctor if these symptoms become severe or do not go away.

The serious side effects of phentermine include dizziness, tremors, shortness of breath, chest pain,  heart palpitations, blood pressure increase, restlessness,  swelling of the legs and ankles, and difficulty of doing exercise that you have been able to do. Call your doctor immediately if you are experiencing any of these phentermine side effects.

Take note that phentermine may cause other side effects other than those listed here. If you have any unusual problems while taking phentermine, tell them to your doctor.


Medline Plus, National Institute of Health


The information in this article is not a substitute for professional medical advice. Please seek advice from your doctor before taking any action suggested on this article.