Phentermine (patient information)
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Why is this medication prescribed
Phentermine is used, in combination with diet and exercise, to help you lose weight. It works by decreasing your appetite.
This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information.
How should this medicine be used
Phentermine comes in tablets and extended-release capsules. It usually is taken as a single daily dose in the morning or three times a day 30 minutes before meals. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take phentermine exactly as directed.
Most people take the drug for 3-6 weeks; the length of treatment depends on how you respond to the medication. Phentermine can be habit-forming. Do not take a larger dose, take it more often, or for a longer period than your doctor tells you to.
To prevent side effects, phentermine should be taken with meals. If you are taking an extended-release (long-acting) product, do not chew or crush the tablet. There are some tablets that can be crushed and mixed with food.
What special precautions should I follow
Before taking phentermine:
- tell your doctor and pharmacist if you are allergic to phentermine or any other drugs.
- tell your doctor and pharmacist what prescription and nonprescription medications you are taking, especially fluoxetine (Prozac), fluvoxamine (Luvox), guanethidine, insulin, MAO inhibitors [phenelzine (Nardil) and tranylcypromine (Parnate)] even if you stopped taking them within the past 2 weeks, medications for weight loss and depression, paroxetine (Paxil), sertraline (Zoloft),and vitamins.
- tell your doctor if you have or have ever had heart disease, high blood pressure, arteriosclerosis (narrowing of the arteries), hyperthyroidism (overactive thyroid gland), diabetes, glaucoma, or a history of drug abuse.
- tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking phentermine, call your doctor.
- you should know that this drug may make you drowsy. Do not drive a car or operate machinery until you know how this drug affects you.
- remember that alcohol can add to the drowsiness caused by this drug.
- if you have diabetes, you may need a larger dose of insulin while taking phentermine. Call your doctor if you have questions or problems.
What special dietary instructions should I follow
Follow the diet and exercise program your doctor has given you. Phentermine works best in combination with a diet program.
What should I do if I forget a dose
Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.
Mild side effects
Phentermine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:
- dry mouth
- unpleasant taste
Severe side effects
If you experience any of the following symptoms, call your doctor immediately:
- increased blood pressure
- heart palpitations
- shortness of breath
- chest pain
- swelling of the legs and ankles
- difficulty doing exercise that you have been able to do
If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online [at http://www.fda.gov/MedWatch/report.htm] or by phone [1-800-332-1088].
What storage conditions are needed for this medicine
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.
In case of emergency/overdose
In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.
What other information should I know
Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your response to phentermine.
Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.