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Phentermine Dosage

Medically reviewed by Last updated on Jul 27, 2023.

Applies to the following strengths: 30 mg; 15 mg; 37.5 mg; 8 mg; 18.75 mg; resin 15 mg; resin 30 mg

Usual Adult Dose for Obesity

8 mg tablet (Lomira): 8 mg orally 3 times a day 30 minutes before meals

  • Some patients may only require 4 mg dose (one-half tablet) 3 times a day

15 and 30 mg capsules: 15 or 30 mg orally approximately 2 hours after breakfast

37.5 mg capsules and tablets (Adipex-P): 37.5 mg orally once a day before breakfast or 1 to 2 hours after breakfast
  • Some patients may only require 18.75 mg (one-half tablet) orally once a day OR 18.75 mg orally twice a day

  • Dosage should be individualized to obtain an adequate response with the lowest effective dose.
  • Late evening dosing should be avoided due to the possibility of insomnia.

Use: Short-term (a few weeks) adjunct in a regimen of weight reduction based on exercise, behavioral modification, and caloric restriction in the management of exogenous obesity in patients with an initial body mass index (BMI) of 30 kg/m2 or greater, or BMI of 27 kg/m2 or greater in the presence of other risk factors (e.g., controlled hypertension, diabetes, hyperlipidemia).

Renal Dose Adjustments

Mild to moderate renal impairment: No adjustment recommended
Severe renal impairment (eGFR 15 to 29 mL/min/1.73 m2): Maximum dose: 15 mg/day
ESRD (eGFR less than 15 mL/min/1.73 m2): Avoid use

Liver Dose Adjustments

No adjustment recommended

Dose Adjustments

Elderly: Dose selection should be cautious, usually starting at the low end of the
dosing range; consider monitoring renal function as this drug is substantially excreted by the kidney



  • History of cardiovascular disease (e.g., arrhythmias, congestive heart failure, coronary artery disease, uncontrolled hypertension, stroke)
  • Hypersensitivity or idiosyncratic reaction to sympathomimetic drugs
  • Hyperthyroidism
  • Agitated states
  • Glaucoma
  • History of drug abuse
  • Use of monoamine oxidase inhibitors concurrently, or within 14 days
  • Breastfeeding
  • Pregnancy

Safety and efficacy have not been established in patients younger than 17 years.

Consult WARNINGS section for additional precautions.

US Controlled Substance: Schedule IV


Not recommended

Other Comments

Administration Advice:

  • Take orally; avoid late evening administration due to the possibility of resulting insomnia

  • This drug is indicated for short-term use in a weight loss program based on exercise, behavioral modification, and caloric restriction.
  • The safety and efficacy of combination therapy with phentermine and any other drug products for weight loss have not been established; coadministration of drug products for weight loss is not recommended.
  • Tolerance to anorectant effect generally develops and if this occurs, this drug should be discontinued; the recommended dose should not be exceeded.

  • Monitor for development of tolerance
  • Consider monitoring renal function in elderly patients
  • Monitor for development of new, unexplained symptoms of dyspnea, angina pectoris, syncope, or lower extremity edema
  • Monitor for potential abuse

Patient Advice:
  • Patients should be informed about the risks of using this drug, potential adverse reactions, and when to contact their healthcare provider.
  • Patients should be instructed to avoid activities that require mental alertness such as driving and operating machinery until they know how this drug affects them.
  • Women who are considering becoming pregnant should speak with their healthcare provider; this drug should not be used by women who are pregnant or breastfeeding.

Frequently asked questions

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.