Phentermine Warnings and Precautions
Let your healthcare provider know if you have diabetes, glaucoma, or high blood pressure before taking phentermine. Warnings and precautions also include avoiding alcohol during treatment, watching out for potential drug interactions, and using the drug only for a short period of time. You should not take phentermine if you have a heart condition, an overactive thyroid, or a history of drug abuse.
You should talk with your healthcare provider prior to taking phentermine if you have:
- Glaucoma (a condition of the eye)
- High blood pressure (hypertension)
- Hyperthyroidism (overactive thyroid)
- Heart problems of any kind, including heart disease, congestive heart failure, certain irregular heart rhythms (arrhythmias), or a recent heart attack
- Ever had a stroke
- A history of drug abuse or alcohol abuse
- Any allergies, including allergies to foods, dyes, or preservatives.
Also, let your healthcare provider know if you are:
- Pregnant or thinking of becoming pregnant
You should also be sure to tell your healthcare provider about all other medicines you are taking, including prescription and prescription medicines, vitamins, and herbal supplements.
Warnings and precautions to be aware of prior to taking phentermine include the following:
- A combination of phentermine and fenfluramine ("phen/fen") has been shown to cause dangerous side effects, including problems with the heart valves and a lung problem known as primary pulmonary hypertension (PPH). It appears that phentermine alone may also cause these problems, although less commonly. Let your healthcare provider known if you have any symptoms of PPH, such as:
- Difficulty breathing
- Chest pain
- Fatigue or weakness
- Dizziness or fainting
- Ankle or leg swelling
- Blue lips or skin.
- Phentermine can increase your heart rate and blood pressure. This can cause problems, especially if you already have high blood pressure or heart problems.
- Phentermine should only be used for short periods of time (no longer than a few weeks). Phentermine is chemically similar to amphetamines, which are often abused, and taking it for long lengths of time can lead to dependence. Because phentermine is often abused, there are special rules for prescribing and dispensing it.
- It is usually best to avoid drinking alcohol while taking phentermine.
- If you have diabetes and take insulin, your healthcare provider may need to adjust your insulin dosage, since phentermine suppresses the appetite.
- Before you take phentermine, your healthcare provide should make sure your obesity is not caused by a medical problem.
- Phentermine may affect your ability to perform tasks that require complete concentration, such as driving, operating machinery, or piloting an airplane, especially during the first few weeks of treatment. It is recommended that you use caution until you know exactly how phentermine affects you.
- The body normally becomes tolerant to the appetite-suppressing effects of this medication within a few weeks. When this happens, the dose should not be increased to try to overcome the body's tolerance. Instead, the medicine should be stopped. Using higher doses than recommended can be dangerous, and may lead to physical dependence and addiction.
- Phentermine can interact with a number of different medications (see Phentermine Drug Interactions for more information).
- Phentermine is considered a pregnancy Category X medication. This means that it is not safe for use during pregnancy and has no role for use during pregnancy. Be sure to talk with your healthcare provider about the risks and benefits of using phentermine during pregnancy (see Phentermine and Pregnancy).
- It is not known if phentermine passes through breast milk. Therefore, if you are breastfeeding or plan to start, discuss this with your healthcare provider prior to taking the drug (see Phentermine and Breastfeeding).