Phentermine is similar to an amphetamine. It stimulates the central nervous system (nerves and brain), which increases your heart rate and blood pressure and decreases your appetite.
Phentermine is used together with diet and exercise to treat obesity, especially in people with risk factors such as high blood pressure, high cholesterol, or diabetes.
Do not use phentermine if you are pregnant or breast-feeding a baby.
You should not use phentermine if you have glaucoma, overactive thyroid, severe heart problems, uncontrolled high blood pressure, advanced coronary artery disease, extreme agitation, or a history of drug abuse.
Do not use this medicine if you have used an MAO inhibitor in the past 14 days, such as isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, or tranylcypromine. A dangerous drug interaction could occur.
Before taking this medicine
You should not use phentermine if you are allergic to it, or if you have:
- a history of heart disease (coronary artery disease, heart rhythm problems, congestive heart failure, stroke);
- severe or uncontrolled high blood pressure;
- overactive thyroid;
- extreme agitation or nervousness;
- a history of drug abuse; or
- if you take other diet pills.
Do not use phentermine if you have used an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, tranylcypromine, and others.
Weight loss during pregnancy can harm an unborn baby, even if you are overweight. Do not use phentermine if you are pregnant. Tell your doctor right away if you become pregnant during treatment.
You should not breast-feed while using this medicine.
To make sure this medicine is safe for you, tell your doctor if you have:
- heart disease or coronary artery disease;
- a heart valve disorder;
- high blood pressure;
- diabetes (your diabetes medication dose may need to be adjusted); or
- kidney disease.
Phentermine is not approved for use by anyone younger than 16 years old.
What should I avoid while taking phentermine?
Avoid driving or hazardous activity until you know how phentermine will affect you. Your reactions could be impaired. Drinking alcohol with this medicine can cause side effects.
Phentermine side effects
Get emergency medical help if you have signs of an allergic reaction to phentermine: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
- feeling short of breath, even with mild exertion;
- chest pain, feeling like you might pass out;
- swelling in your ankles or feet;
- pounding heartbeats or fluttering in your chest;
- tremors, feeling restless, trouble sleeping;
- unusual changes in mood or behavior; or
- increased blood pressure – severe headache, blurred vision, pounding in your neck or ears, anxiety, nosebleed.
Common phentermine side effects may include:
- dizziness, headache;
- dry mouth, unpleasant taste;
- diarrhea, constipation, stomach pain; or
- increased or decreased interest in sex.
What other drugs will affect phentermine?
Taking phentermine together with other diet medications such as fenfluramine which can cause a rare fatal lung disorder called pulmonary hypertension. Do not take phentermine with any other diet medications without your doctor’s advice.
Many drugs can interact with phentermine. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.
What happens if I miss a dose?
Take the medicine as soon as you can, but skip the missed dose if it is late in the day. Do not take two doses at one time.
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use phentermine only for the indication prescribed.