Phentermine

Phentermine is a controlled medication used for weight loss. Try to avoid drinking large amounts of beverages containing caffeine. Avoid drinking alcohol while taking this medication.

Phentermine Overview

Reviewed: April 8, 2013
Updated: 

Phentermine is a prescription medicine used for weight loss.  It is taken for a limited amount of time by overweight adults, along with exercise and a low-fat diet. Phentermine belongs to a group of drugs called anorectics. It works by decreasing appetite.

Phentermine comes in tablet and capsule form. It usually taken by mouth once daily in the morning before breakfast or 1 to 2 hours after breakfast.

Phentermine also is available as an orally disintegrating tablet and is usually taken in the morning, with or without food.

Common side effects of phentermine include dry mouth, fast heart beat, insomnia, and dizziness.

Do not drive or operate heavy machinery until you know how phentermine affects you.

 

Patient Ratings for Phentermine

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  • Obesity

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Phentermine Cautionary Labels

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Uses of Phentermine

Phentermine is a prescription medicine used to help adults lose weight.  It is taken for a limited amount of time by overweight people who are exercising and eating a low-calorie diet.

This medication may be prescribed for other uses.  Ask your doctor or pharmacist for more information.

Phentermine Brand Names

Phentermine may be found in some form under the following brand names:

Phentermine Drug Class

Phentermine is part of the drug class:

Side Effects of Phentermine

Phentermine can cause primary pulmonary hypertension, a rare but serious and sometimes fatal side effect. This is a condition where the pressure of the arteries in your lungs increases, causing more pressure on your heart which can lead to heart failure and death. The first symptoms is often shortness of breath or lightheadedness during activity. Other symptoms include:

  • Ankle and leg swelling
  • Bluish color of the lips or skin 
  • Chest pain or pressure, usually in the front of the chest
  • Dizziness or fainting spells
  • Tiredness
  • Increased abdomen size
  • Weakness

Common side effects include:

  • High blood pressure
  • fast heart beats
  • insomnia
  • dizziness
  • rash
  • diarrhea
  • tremors
  • constipation

This is not a complete list of phentermine side effects. Ask your doctor or pharmacist for more information.

Phentermine Interactions

Tell your doctor about all the medicines you take including prescription and nonprescription medications, vitamins, and herbal supplements. Especially tell your doctor if you take:

  • fluoxetine (Prozac)
  • fluvoxamine (Luvox) 
  • guanethidine
  • oral hypoglycemic medications for diabetes
  • insulin (you may need to increase your dose of insulin while taking phentermine)
  • medications for weight loss and depression
  • paroxetine (Paxil)
  • sertraline (Zoloft)
  • monoamine oxidase (MAO) inhibitors such as isocarboxazid (Marplan), phenelzine (Nardil), selegiline (Eldepryl, Emsam, Zelapar) and tranylcypromine (Parnate)

This is not a complete list of phentermine drug interactions. Ask your doctor or pharmacist for more information.

 

Phentermine Precautions

Serious side effects have been reported with phentermine including the following:

  • Primary pulmonary hypertension. This is a condition when there is high blood pressure in the arteries to your lungs. Your doctor may stop treatment with phentermine if you develop this complication. Symptoms include
    • shortness of breath during routine activity, such as climbing two flights of stairs
    • tiredness
    • chest pain
    • a racing heartbeat
    • pain on the upper right side of the abdomen
    • decreased appetite
  • Development of Tolerance. Phentermine is a controlled substance. There is a potential for developing tolerance. Tolerance to the anorectic effect usually develops within a few weeks. When tolerance to the phentermine develops, the recommended dose should not be exceeded in an attempt to increase the effect. Instead phentermine should be discontinued.
  • Effect on the Ability to Engage in Potentially Hazardous Tasks.  Phentermine may impair the ability of the patient to drive or operate heavy machinery. Do not drive or operate heavy machinery until you know how phentermine affects you.

  • Risk of Abuse and Dependence. Phentermine should not be stopped all of a sudden especially if phentermine dose is high. This can lead to serious problems.

  • Valvular heart disease.

Drinking alcohol with phentermine may result in an adverse drug reactions.

You should not take phentermine if you have:

  • are allergic to phentermine or to any of its ingredients
  • heart disease
  • lung disease
  • hyperthyroidism
  • glaucoma
  • a history of drug abuse or dependence
  • agitated state
  • depression being treated with certain antidepressant medications called MAOI inhibitors

Phentermine should not be used during pregnancy or while breastfeeding.

 

Phentermine Food Interactions

While there are no specific phentermine food interactions, you should avoid drinking large amounts of beverages containing caffeine (coffee, tea, colas) or eating large amounts of chocolate while taking phentermine as caffeine can increase the side effects of this medicine.

 

Inform MD

Before taking phentermine, tell your doctor about all of your medical conditions. Especially tell your doctor if you:

  • are allergic to phentermine or to any of its ingredients
  • have high blood pressure
  • drink alcohol
  • a history of drug abuse or dependence
  • decreased kidney function
  • have diabetes
  • are pregnant or breastfeeding

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements.

Phentermine and Pregnancy

Tell your doctor if you are pregnant or plan to become pregnant.

The FDA categorizes medications based on safety for use during pregnancy. Five categories - A, B, C, D, and X, are used to classify the possible risks to an unborn baby when a medication is taken during pregnancy.

Phentermine falls into category X. Phentermine should not be used during pregnancy because weight loss offers no potential benefit to a pregnant woman and may result in fetal harm. There are no situations where the benefits of the medication for the mother outweigh the risks of harm to the baby. These medicines should never be used by pregnant women.

Phentermine and Lactation

Tell your doctor if you are breastfeeding or plan to breastfeed.

It is not known if phentermine crosses into human milk. Because many medications can cross into human milk and because of the possibility for serious adverse reactions in nursing infants with use of this medication, a choice should be made whether to stop nursing or stop the use of this medication. Your doctor and you will decide if the benefits outweigh the risk of using phentermine.

Phentermine Usage

Take phentermine exactly as prescribed.

Phentermine comes in tablet, capsule. It usually taken by mouth once daily in the morning before breakfast or 1 to 2 hours after breakfast.

Phentermine also is available as an orally disintegrating tablet form and is usually taken in the morning, with or without food.

Taking phentermine in the evening can cause insomnia (trouble falling asleep or staying asleep), so phentermine should be taken in the morning.

With dry hands, gently remove the Suprenza (phentermine hydrochloride ODT) tablet from the bottle. Immediately place the tablet on top of the tongue where it will dissolve, then swallow with or without water.

Do not drink alcohol while taking phentermine.

If you miss a dose, take the missed dose as soon as you remember. If it is almost time for the next dose, skip the missed dose and take your next dose at the regular time. Do not take two doses of phentermine at the same time.

Phentermine Dosage

Take this medication exactly as prescribed by your doctor. Follow the directions on your prescription label carefully.

The dose your doctor recommends will be individualized to obtain an adequate response with the lowest effective dose.

Phentermine Tablets and Capsule

The typical adult dose is 37.5 mg daily administered before breakfast or 1 to 2 hours after breakfast. The dosage may be adjusted to the patient’s need. For some patients, 18.75 mg daily may be adequate. 

In some cases it may be desirable to give 18.75 mg two times a day.

Phentermine orally disintegrating tablet

The typical adult dose is one tablet in the morning, with or without food.

Suprenza is available as 15 mg, 30 mg, or 37.5 mg orally disintegrating tablets.

 

Phentermine Overdose

If you take too much phentermine, call your healthcare provider or local Poison Control Center, or seek emergency medical attention right away.

 

Other Requirements

  • Store phentermine at 20° to 25°C (68° to 77°F).
  • Keep this and all medicines out of the reach of children.