• Basic Info
• Top Questions
• Clinical Info
• Interactions

What is phentermine?
Phentermine is a stimulant that is similar to an amphetamine. Phentermine is an appetite suppressant that affects the central nervous system. Phentermine is used togther with diet and exercise to treat obesity (overweight) in people with risk factors such as high blood pressure, high cholesterol, or diabetes. Phentermine may also be used for other purposes not listed in this medication guide.

Back to Top

What is the price of this medication and similar alternatives?

This pricing information is subject to change at the sole discretion of DS Pharmacy. For the most current and up-to-date pricing information, please visit drugstore.com.

Back to Top

What are the possible side effects of phentermine?

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop using phentermine and call your doctor at once if you have any of these serious side effects:

• feeling short of breath, even with mild exertion;

• swelling, rapid weight gain;

• chest pain, fast or uneven heartbeat, feeling like you might pass out;

• unusual thoughts or behavior, feeling restless or confused; or

• dangerously high blood pressure (severe headache, blurred vision, buzzing in your ears, anxiety, confusion, chest pain, shortness of breath, uneven heartbeats, seizure).

Less serious side effects may include:

• feeling nervous or anxious;

• headache, dizziness, tremors;

• trouble sleeping (insomnia);

• dry mouth or an unpleasant taste in your mouth;

• diarrhea or constipation; or

• itching.

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect.

Back to Top

How should I take phentermine?
Take this medication exactly as it was prescribed for you. Do not take the medication in larger amounts, or take it for longer than recommended by your doctor. Follow the directions on your prescription label. It is best to take phentermine on an empty stomach before breakfast, or at least 10 to 14 hours before bedtime. Do not take more phentermine for an increased effect. Taking too much of this medication can cause serious, life-threatening side effects. Do not crush, chew, break, or open an extended-release capsule. Swallow the pill whole. It is specially made to release medicine slowly in the body. Breaking or opening the pill would cause too much of the drug to be released at one time.

Back to Top

What is the most important information I should know about phentermine?
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. Phentermine can cause side effects that may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be awake and alert. Avoid drinking alcohol. It can increase some of the side effects of phentermine.

Back to Top

What happens if I miss a dose?
Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and take the medicine at your next regularly scheduled time. Do not take extra medicine to make up the missed dose.

Back to Top

What other drugs will affect phentermine?
Before taking phentermine, tell your doctor if you are using any of the following drugs: medicines to treat high blood pressure; insulin or diabetes medication you take by mouth; guanadrel (Hylorel), guanethidine (Ismelin); antidepressants such as citalopram (Celexa), escitalopram (Lexapro), fluoxetine (Prozac, Sarafem), fluvoxamine (Luvox), paroxetine (Paxil), or sertraline (Zoloft); or antidepressants such as amitriptyline (Elavil, Etrafon), amoxapine (Ascendin), clomipramine (Anafranil), desipramine (Norpramin), doxepin (Sinequan), imipramine (Janimine, Tofranil), nortriptyline (Pamelor), protriptyline (Vivactil), or trimipramine (Surmontil).

Back to Top

Can I take this if I am pregnant or trying to get pregnant or if I am breastfeeding?

Phentermine has not been formally assigned to a pregnancy category by the FDA. There are no controlled data in human pregnancy. Phentermine should only be given during pregnancy when benefit outweighs the risk.

There are no data on the excretion of phentermine into human milk.

Back to Top

Who should NOT use this medication?

• Symptomatic cardiovascular disease, hyperthyroidism, moderate to severe hypertension, glaucoma, or advanced arteriosclerosis.
• Agitated state or history of drug abuse.
• Within 14 days of MAO inhibitor therapy.
• Known hypersensitivity or idiosyncrasy to sympathomimetic amines.

Back to Top

What happens if I overdose?
Seek emergency medical attention if you think you have used too much of this medication. An overdose of phentermine can be fatal. Overdose symptoms may include confusion, hallucinations, feeling restless or aggressive, nausea, vomiting, diarrhea, stomach pain, irregular heartbeat, tremors, rapid breathing, confusion, hallucinations, feeling light-headed, fainting, or seizure (convulsions).

Back to Top

What should I discuss with my healthcare provider before taking phentermine?
Do not take phentermine if you have used an MAO inhibitor such as isocarboxazid (Marplan), phenelzine (Nardil), rasagiline (Azilect), selegiline (Eldepryl, Emsam), or tranylcypromine (Parnate) within the past 14 days. Serious, life-threatening side effects can occur if you take phentermine before the MAO inhibitor has cleared from your body. 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.

Back to Top

Can I stop taking the medication if I feel better?
As a general rule, you should always take your medications exactly as prescribed and do not change the dosage or stop taking the medication without first discussing it with your healthcare provider.

Back to Top

I am on so many medications; do I have to take them all?
This is called polypharmacy—many different medications being used at the same time by one person. Sometimes, being on multiple medications is acceptable and appropriate but at other times it may be problematic. If you are receiving your medications from multiple physicians you need to ensure that they all know what medications you are taking. The best way to do this is to make a list of all the medications you are currently using, including all nutritional supplements, homeopathic remedies, vitamins and over-the-counter drugs (if possible, also include all the diseases you have been diagnosed with). Give a copy to every doctor who takes care of you so they have it on file, this way they can avoid duplicating medications and perhaps even try to consolidate some. After every doctor's visit remember to update the list accordingly. Also, as much as you possibly can, try to use the same pharmacy to fill all your prescriptions, this way any potential drug interactions can be caught and averted.

Back to Top

Where can I get more information?
More Information

Back to Top