Possible side effects of Phentermine :
All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome:
Bad taste in mouth; changes in sex drive; constipation; diarrhea; difficulty sleeping; dizziness; dry mouth; exaggerated sense of well being; headache; impotence; nervousness; overstimulation; restlessness; sleeplessness; upset stomach.
Seek medical attention right away if any of these SEVERE side effects occur:
Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); bizarre behavior; chest pain; fainting; fast heartbeat; pounding in the chest; shortness of breath; swelling of the legs and feet; tremor.
This is not a complete list of all side effects that may occur. If you have questions or need medical advice about side effects, contact your doctor or health care provider. You may report side effects to the FDA at 1-800-FDA-1088 (1-800-332-1088) or at http://www.fda.gov/medwatch.