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Phentermine Side Effects

Medically reviewed by Last updated on Nov 10, 2022.

Applies to phentermine: oral phentermine hydrochloride capsules and tablets, oral phentermine resin complex capsules.

Side effects include:

Palpitation, tachycardia, increased BP, overstimulation, restlessness, insomnia, tremor, dizziness, headache, euphoria, dysphoria, dryness of the mouth, unpleasant taste, diarrhea, constipation, vomiting, other GI disturbances, urticaria, impotence, changes in libido.

For Healthcare Professionals

Applies to phentermine: compounding powder, oral capsule, oral capsule extended release, oral tablet, oral tablet disintegrating.


The more commonly reported adverse reactions have included palpitations, restlessness, insomnia, and headache.


Frequency not reported: Regurgitant cardiac valvular disease, primary pulmonary hypertension, palpitations, tachycardia, elevated blood pressure, precordial pain, ischemic events, angina, myocardial infarction, cardiac failure, cardiac arrest[Ref]

Nervous system

Frequency not reported: Overstimulation, restlessness, nervousness, dizziness, euphoria, dysphoria, tremor, headache, fatigue, cerebrovascular events[Ref]


Frequency not reported: Insomnia, psychosis, impotence, libido changes, depression, hallucinations[Ref]


Frequency not reported: Urticaria[Ref]


Frequency not reported: Dry mouth, unpleasant taste, diarrhea, constipation, other gastrointestinal disturbances, nausea, vomiting, abdominal cramps[Ref]


Frequency not reported: Rash[Ref]


Frequency not reported: Micturition disturbances[Ref]


Frequency not reported: Facial edema[Ref]

Frequently asked questions


1. Cerner Multum, Inc. Australian Product Information.

2. Product Information. Phentermine Hydrochloride (phentermine). Teva Pharmaceuticals USA. 2016.

3. Product Information. Adipex-P (phentermine). Teva Pharmaceuticals (formerly Gate Pharmaceuticals). 2016.

4. Product Information. Lomaira (phentermine). KVK-Tech Inc. 2016.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.