Phentermine is used for a limited period of time to speed weight loss in overweight people who are exercising and eating a low-calorie diet. Phentermine is in a class of medications called anorectics. It works by decreasing appetite.
Phentermine comes as 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 takephentermine 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 take it for a longer period than your doctor tells you to.
If you are taking the extended-release (long-acting) tablets, do not split, chew, or crush them tablet. There are some tablets that can be crushed and mixed with food.
This medication may be prescribed for other uses. Ask your doctor or pharmacist for more information.
Before taking phentermine,
- tell your doctor and pharmacist if you are allergic to phentermine, any other medications, or any of the ingredients in phentermine tablets. Ask your pharmacist for a list of the ingredients.
- tell your doctor and pharmacist what prescription and nonprescription medications, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: fluoxetine (Prozac), fluvoxamine (Luvox), guanethidine, insulin medications for weight loss and depression, paroxetine (Paxil), and sertraline (Zoloft). Also tell your doctor if you are taking monoamine oxidase (MAO) inhibitors such as isocarboxazid (Marplan), phenelzine (Nardil), selegiline (Eldepryl, Emsam, Zelapar) and tranylcypromine (Parnate), or if you have stopped taking one of these medications in the past 2 weeks. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
- 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.
- talk to your doctor about the risks and benefits of taking phentermine if you are 65 years of age or older. Older adults should not usually take phentermine because it is not as safe as other medications that can be used to treat the same condition.
- you should know that this medication may make you drowsy. Do not drive a car or operate machinery until you know how this medication affects you.
- ask your doctor about the safe use of alcohol while you are taking phentermine. Alcohol can make the side effects of phentermine worse.
- if you have diabetes, you may need to decrease your dose of insulin while taking phentermine. Call your doctor if you have questions or problems.
Follow the diet and exercise program your doctor has given you. Phentermine works best in combination with a diet program.
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.
Phentermine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:
- dry mouth
- unpleasant taste
Some side effects can be serious. 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
Phentermine may cause other side effects. Call your doctor if you have any unusual problems during your treatment with phentermine.
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 Web Site] or by phone [1-800-332-1088].
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 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.
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. Phenteramine is a controlled substance. Prescriptions may be refilled only a limited number of times; ask your pharmacist any questions you have about refilling your prescription.
It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.
AHFS® Consumer Medication Information. © Copyright, The American Society of Health-System Pharmacists, Inc., 7272 Wisconsin Avenue, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.
Selected Revisions: October 15, 2011.