Phentermine Side Effects

Phentermine is a stimulant that is similar to an amphetamine. Phentermine is an appetite suppressant that affects the central nervous system.

Phentermine is used together with diet and exercise to treat obesity (overweight) in people with risk factors such as high blood pressure, high cholesterol, or diabetes.

Do not use phentermine if you have used an MAO inhibitor such as furazolidone (Furoxone), isocarboxazid (Marplan), phenelzine (Nardil), rasagiline Azilect), selegiline (Eldepryl, Emsam, Zelapar), or tranylcypromine (Parnate) in the last 14 days. A dangerous drug interaction could occur, leading to serious side effects.

Taking phentermine together with other diet medications such as fenfluramine (Phen-Fen) or dexfenfluramine (Redux) can cause a rare fatal lung disorder called pulmonary hypertension. Do not take tbis medicine with any other diet medications without your doctor’s advice.

You should not take 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, pulmonary hypertension);
  • severe or uncontrolled high blood pressure;
  • overactive thyroid;
  • glaucoma;
  • if you are pregnant or breast-feeding;
  • if you are in an agitated state;
  • if you have a history of drug or alcohol abuse; or
  • if you are allergic to other diet pills, amphetamines, stimulants, or cold medications.

To make sure you can safely take phentermine, tell your doctor if you have any of these other conditions:

  • high blood pressure;
  • diabetes;
  • kidney disease; or
  • a thyroid disorder.

FDA pregnancy category X. Weight loss during pregnancy can harm an unborn baby, even if you are overweight. Do not use phentermine if you are pregnant. Phentermine can pass into breast milk and may harm a nursing baby. You should not breast-feed while taking phentermine. Do not give this medication to a child younger than 16 years old.

Get emergency medical help if you have any of these signs of an allergic reaction to phentermine: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Call your doctor at once if you have a serious side effect such as:

  • 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;
  • confusion or irritability, unusual thoughts or behavior;
  • feelings of extreme happiness or sadness; or
  • dangerously high blood pressure (severe headache, blurred vision, buzzing in your ears, anxiety, chest pain, shortness of breath, uneven heartbeats, seizure).

Less serious phentermine side effects may include:

  • feeling restless or hyperactive;
  • headache, dizziness, tremors;
  • sleep problems (insomnia);
  • dry mouth or an unpleasant taste in your mouth;
  • diarrhea or constipation, upset stomach; or
  • increased or decreased interest in sex, impotence.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

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