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What does it do?

Phentermine is used to help you lose weight.

Before you start

  • Tell your doctor if you have heart or kidney problems, high blood pressure, angle-closure glaucoma, or if you have ever had a stroke.
  • Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding.

How should you take it?

Take phentermine as part of a weight loss plan from a health professional.
Take phentermine regularly as directed with a glass of water. Swallow the capsules whole.
It is best to take phentermine in the morning as it can cause trouble sleeping.

What if you forget a dose?

If it is after lunchtime, skip the missed dose and take your next dose at the usual time. Otherwise, take the missed dose as soon as you remember. Do not take two doses at the same time.

Can you take other medicines?

Tell your pharmacist or doctor about all medicines or treatments that you may be taking, including vitamins, herbal products or recreational drugs.

What side effects might you notice?

Side EffectsRecommended action

Chest pain

Tell your doctor immediately

Fast or irregular heartbeat

Swollen feet or legs, short of breath

Unusual behaviour or thinking

Tell your doctor

Trouble sleeping, restlessness, nervousness


Dry mouth, unpleasant taste

Stomach upset

Trouble getting or keeping an erection

Tell your doctor if troublesome

If you notice any other effects, discuss them with your doctor or pharmacist.

This leaflet contains important, but not all, information about this medicine.

Prepared by the MyMedicines Committee at Christchurch Hospital, Te Whatu Ora - Waitaha, New Zealand. March 2023

For more general information about this sheet and its contents, see: What does a My Medicines sheet cover?

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About My Medicines

My Medicines Patient Information Leaflets (PILs) contain important, but not all, information about the medicines they describe.

For more information about the sheets, see: What does a My Medicines sheet cover?

My Medicines is developed by a team at Te Whatu Ora – Waitaha. Our team is made up of doctors, pharmacists, and a non-medical person to help us keep to plain language. We also discuss our information with specialist health professionals or groups when needed