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Phentermine for Weight Loss

Supportive Care

Brand names:

Lomaira®

Other names:

Phentermine hydrochloride

Often used for:

Weight loss

This information is specific to the use of phentermine for weight loss. For additional information on phentermine, please talk to your health care provider.

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What is phentermine?

Phentermine is a medicine used to reduce appetite and help patients lose extra body weight. It also works as a stimulant to increase energy levels.

Phentermine is used as a short-term support for weight loss. Phentermine may be given along with other weight loss medicines. It works best when combined with a low-calorie diet and exercise program. 

Your care team will monitor your heart function while taking this medicine.

Brain

May be given as a capsule by mouth

 
Brain

May be given as a tablet by mouth

 
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Possible side effects

  • Excitability, restlessness, or nervousness
  • Sleep problems
  • Mood changes
  • Headache
  • Dry mouth
  • Changes in taste
  • Increased heart rate
  • Increased blood pressure
  • Constipation or diarrhea
  • Tremors (shaking of the body)
  • Decreased sex drive

Call your care team right away if your child has symptoms of an allergic reaction. These may include: rash, hives, itching, runny nose, fever, chills, headache, muscle ache, shortness of breath, coughing, tightness in the throat, swelling of the face or neck, dizziness, low blood pressure, or pain in the chest, side, or back.   

Not all patients who take phentermine will have these side effects. Common side effects are in bold, but there may be others. Report any symptoms or side effects to your health care provider or pharmacist. 

Find more information on side effects.

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Tips for patients and families

Be sure to discuss all questions and instructions with your health care provider or pharmacist.

  • Phentermine works best when used along with a nutrition and exercise program.
  • Do not take phentermine for a longer time than prescribed by your health care provider.
  • You may have changes in your mood or mental health, such as worsening depression, anxiety, agitation, irritability, panic attacks, and trouble sleeping.
  • Tell your care team if you are sexually active, pregnant, or breastfeeding.
  • Sexually active patients should take steps to prevent pregnancy during treatment.

Phentermine at home:

  • Tablets: Take as directed. Scored tablets may be cut in half.
  • In case of a missed dose, give the missed dose as soon as possible. If it is near the time for the next dose, skip the missed dose. Do not give 2 doses at the same time. 
  • Store at room temperature in a dry place. Do not store in a bathroom.
  • This drug may be habit-forming with long-term use. Watch for signs of misuse. 

Learn more about phentermine

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Always check the medication label. Many medicines look the same. Do not take any new medicine, including over-the counter medicines or supplements, without checking with your doctor or pharmacist. Talk to your doctor or pharmacist about what to do in the case of a missed dose, allergic reaction, or medical emergency. 

This information is not intended to be a complete guide and is not a substitute for talking with your provider. Medicine names, appearance, formulas, or availability may vary by clinic location. Always follow the instructions given by your care team.

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Reviewed: January 2026