Phentermine Dosage

Medically reviewed by Drugs.com. Last updated on Jul 27, 2023.

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

Comments:

• 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

Precautions

CONTRAINDICATIONS:

• 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

Dialysis

Not recommended

Other Comments

Administration Advice:

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

General:

• 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.

Monitoring:

• 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

• Why is phentermine a controlled substance?

Further information

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

Medical Disclaimer