Save up to 80% on brand & generic medications.
Save on these medications!
Learn more about price differences between brand and generic drugs
Get the Inside Rx app
Frequently Asked Questions
You should not use this medicine if you have glaucoma, overactive thyroid, severe heart problems, uncontrolled high blood pressure, advanced coronary artery disease, extreme agitation, or a history of drug abuse.
Do not use this medicine if you have used an MAO inhibitor in the past 14 days, such as isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, or tranylcypromine.
Phentermine is similar to an amphetamine. Phentermine stimulates the central nervous system (nerves and brain), which increases your heart rate and blood pressure and decreases your appetite.
Phentermine is used together with diet and exercise to treat obesity, especially in people with risk factors such as high blood pressure, high cholesterol, or diabetes.
Phentermine may also be used for purposes not listed in this medication guide.
You should not use phentermine if you are allergic to it, or if you have:
- a history of heart disease (coronary artery disease, heart rhythm problems, congestive heart failure, stroke);
- severe or uncontrolled high blood pressure;
- overactive thyroid;
- extreme agitation or nervousness;
- a history of drug abuse; or
- if you take other diet pills.
Do not use phentermine if you have used an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, tranylcypromine, and others.
Weight loss during pregnancy can harm an unborn baby, even if you are overweight. Do not use phentermine if you are pregnant. Tell your doctor right away if you become pregnant during treatment.
You should not breast-feed while using phentermine.
Tell your doctor if you have ever had:
- heart disease or coronary artery disease;
- a heart valve disorder;
- high blood pressure;
- diabetes (your diabetes medication dose may need to be adjusted); or
- kidney disease.
Phentermine is not approved for use by anyone younger than 16 years old.
Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.
Phentermine is usually taken before breakfast, or 1 to 2 hours after breakfast. Follow your doctor's dosing instructions very carefully.
Never use phentermine in larger amounts, or for longer than prescribed. Taking more of this medication will not make it more effective and can cause serious, life-threatening side effects.
Phentermine is for short-term use only. The effects of appetite suppression may wear off after a few weeks.
Phentermine may be habit-forming. Misuse can cause addiction, overdose, or death. Selling or giving away this medicine is against the law.
Call your doctor at once if you think this medicine is not working as well, or if you have not lost at least 4 pounds within 4 weeks.
Do not stop using phentermine suddenly, or you could have unpleasant withdrawal symptoms. Ask your doctor how to safely stop using this medicine.
Store at room temperature away from moisture and heat. Keep the bottle tightly closed when not in use.
Take the medicine as soon as you can, but skip the missed dose if it is late in the day. Do not take two doses at one time.
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phentermine can be fatal.
Overdose symptoms may include confusion, panic, hallucinations, extreme restlessness, nausea, vomiting, diarrhea, stomach cramps, feeling tired or depressed, irregular heartbeats, weak pulse, seizure, or slow breathing (breathing may stop).
Avoid driving or hazardous activity until you know how this medicine will affect you. Your reactions could be impaired.
Drinking alcohol with this medicine can cause side effects.
Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
- 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;
- tremors, feeling restless, trouble sleeping;
- unusual changes in mood or behavior; or
- increased blood pressure--severe headache, blurred vision, pounding in your neck or ears, anxiety, nosebleed.
Common side effects may include:
- dizziness, headache;
- dry mouth, unpleasant taste;
- diarrhea, constipation, stomach pain; or
- increased or decreased interest in sex.
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.
Taking phentermine together with other diet medications such as fenfluramine (Phen-Fen) or dexfenfluramine (Redux) can cause a rare fatal lung disorder called pulmonary hypertension. Do not take phentermine with any other diet medications without your doctor's advice.
Many drugs can affect phentermine. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.
Your pharmacist can provide more information about phentermine.
|Brand Name Examples||Supplied As||Strength|
|Phentermine Hydrochloride||Tablet||37.5 Mg|
|Capsule||15 Mg30 Mg37.5 Mg|
|Generic Examples||Supplied As||Strength|
|Phentermine Hcl||Tablet||37.5 Mg|