What is Phentermine Hcl: Uses, Warnings & Interactions

Updated Feb 14, 2024  •  Published Dec 30, 2020

Phentermine Hcl overview

BRAND NAMES:

  • Adipex-P

  • Lomaira

Generic Names:

  • Phentermine HCI

Uses:

  • Short-term appetite suppressant to help weight loss

Therapeutic Classes:

  • Appetite suppressant (anorectic), stimulant, sympathomimetic

Forms:

  • Tablet, capsule, orally disintegrating tablet

How it’s taken:

  • By mouth

What is Phentermine Hcl used for?

Phentermine HCL is a medication used to suppress appetite. Along with diet, exercise, and behavior changes, this helps people with a BMI of 30 kg/m2 (or 27 kg/m2 in people with certain risk factors) speed up weight loss.

What form(s) does Phentermine Hcl come in

  • Tablet

    • 8 mg, 37.5 mg

  • Capsule

    • 37.5 mg

  • Orally disintegrating tablet

    • 15 mg

    • 30 mg

    • 37.5 mg

What are common Phentermine Hcl doses?

  • For weight loss in adults and adolescents 16 years of age and older: 15–37.5 mg daily

RELATED: Phentermine dosage, forms, and strengths

Common Phentermine Hcl prescriptions

  • Phentermine HCl
    30 capsules bottle

  • Phentermine HCl
    15mg capsule

  • Phentermine HCl
    30mg capsule

  • Phentermine HCl
    37.5mg capsule

  • Phentermine HCl
    37.5mg tablet

How to take Phentermine Hcl

  • Your doctor will tell you how much medicine to use. Do not use more than directed.

  • Take the 37.5 mg tablet or capsule before breakfast or one to two hours after breakfast.

    • Swallow the tablet or capsule whole with a glass of water.

  • Take the Lomaira tablet (8 mg tablet) three times per day 30 minutes before a meal.

    • Swallow the tablet whole with a glass of water.

    • Lomaira tablets are scored so that they can be divided into two 4 mg doses. Ask the healthcare provider or pharmacist how to divide tablets if you are prescribed a lower dose.

    • Avoid taking Lomaira tablets late in the evening because the dose could interfere with sleep.

  • The orally disintegrating tablets are taken in the morning with or without food.

    • Remove the orally disintegrating tablet gently from the bottle with dry hands.

    • Place the tablet immediately on the tongue.

    • Allow it to completely dissolve on the tongue.

    • Then swallow with or without a glass of water.

  • Swallow the tablet whole with a drink of water.

  • Store phentermine tablets or capsules in a closed container at room temperature out of the reach of children.

What to do if you miss a dose of Phentermine Hcl

  • Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. 

  • Do not take extra medicine to make up for a missed dose.

Phentermine Hcl contraindications

  • This medicine is not right for everyone. 

  • Do not take phentermine if you have had an allergic reaction to phentermine or similar medicines.

  • Do not take phentermine if you have:

    • A history of cardiovascular disease including uncontrolled high blood pressure

    • Overactive thyroid

    • Glaucoma

    • Agitated states

    • End-stage kidney disease

    • A history of drug abuse

  • Do not take phentermine if you are pregnant or breastfeeding.

Phentermine Hcl warnings

  • It is not safe to take this medicine during pregnancy. Weight loss could harm an unborn baby. Tell your doctor right away if you become pregnant.

  • Do not breastfeed when taking phentermine.

  • This medicine is not for long-term use.

  • Tell any doctor or other healthcare provider who treats you that you are using this medicine.

  • Your doctor may do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.

  • Phentermine is a controlled substance because of its risk of physical dependence, misuse, overdose, and theft.

    • Do not use phentermine for longer than a few weeks.

    • Do not use more than the prescribed dose.

    • Giving phentermine to another person is against the law.

    • Store this medicine out of the reach of children and other people.

  • Tell your doctor if you have:

    • Kidney disease

    • Diabetes

    • Glaucoma

    • Congestive heart failure

    • Heart or blood vessel disease

    • Heart valve problems

    • A history of stroke

    • High blood pressure

    • Overactive thyroid

    • Problems with agitation

    • A history of drug abuse

  • This medicine may cause the following problems:

    • Primary pulmonary hypertension (a serious lung problem)

    • Heart valve disease

    • Increase in blood pressure

    • Changes in blood sugar levels

  • This medicine may make you dizzy or drowsy. Do not drive or do anything else that could be dangerous until you know how this medicine affects you.

  • Do not stop using this medicine suddenly. Your doctor will need to slowly decrease your dose before you stop it completely.

Phentermine Hcl interactions

  • To avoid potentially hazardous drug interactions, tell the prescribing healthcare provider about all prescription drugs, over-the-counter medicines, and supplements you are using before taking atorvastatin.

  • Tell other healthcare providers you are using this medicine before they prescribe new medications.

  • Do not use this medicine and an MAO inhibitor (MAOI) within 14 days of each other.

  • When taking phentermine, avoid other weight loss drugs or remedies unless cleared by the doctor. This not only includes weight loss drugs purchased with or without a prescription, but weight loss supplements and herbal products, as well. 

  • It may not be safe to take phentermine with SSRIs or amphetamines.

  • Phentermine can decrease the effectiveness of insulin and other diabetes medications, so dosages may need to be adjusted when phentermine is being used.

  • Do not drink alcohol while you are using this medicine.

Phentermine Hcl side effects

Serious side effects 

Talk to a healthcare provider if you notice any signs or symptoms of a possible serious side effect, including:

  • Chest pain, fainting, trouble breathing, swelling of your feet or legs, blue skin or lips, dry cough

  • Fast, slow, pounding, or uneven heartbeat

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing

Less serious side effects

  • Restlessness

  • Trouble sleeping

  • Headache

  • Dizziness

  • Nausea

  • Dry mouth

  • Bad taste in the mouth

  • Changes in sex drive