What happens if I miss a dose?
Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phentermine can be fatal.
What should I avoid?
Drinking alcohol can increase certain side effects.
Phentermine may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.
Phentermine side effects
Get emergency medical help if you have any of these signs of an allergic reaction to phentermine: hives; wheezing, chest tightness, trouble breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have a serious side effect such as:
- Feeling short of breath, even with mild exertion;
- Chest pain, feeling like you might pass out;
- Swelling in your ankles or feet;
- Pounding heartbeats or fluttering in your chest;
- Confusion or irritability, unusual thoughts or behavior;
- Feelings of extreme happiness or sadness; or
- Dangerously high blood pressure (severe headache, blurred vision, buzzing in your ears, anxiety, chest pain, shortness of breath, uneven heartbeats, seizure).
Common phentermine side effects may include:
- Feeling restless or hyperactive;
- Headache, dizziness, tremors;
- Sleep problems (insomnia);
- Dry mouth or an unpleasant taste in your mouth;
- Diarrhea or constipation, upset stomach; or
- Increased or decreased interest in sex, impotence.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
Phentermine dosing information
Usual Adult Dose for Weight Loss:
15 to 37.5 mg orally once a day before breakfast or 1 to 2 hours after breakfast.
Usual Pediatric Dose for Weight Loss:
17 years or older:
15 to 37.5 mg orally once a day before breakfast or 1 to 2 hours after breakfast.
What other drugs will affect phentermine?
Taking this medicine with other stimulant drugs that make you restless or hyperactive can worsen these effects. Ask your doctor before taking phentermine with diet pills, other stimulants, or medicine to treat attention deficit hyperactivity disorder (ADHD).
Tell your doctor about all medicines you use, and those you start or stop using during your treatment with phentermine, especially:
- an antidepressant–citalopram, escitalopram, fluoxetine, fluvoxamine, paroxetine, sertraline.