What is the proper dosing and prescription protocol for phentermine (Adipex-P) for weight loss?

From the Guidelines

Phentermine should be prescribed at a dosage of 15-37.5 mg once daily, taken in the morning, as part of a comprehensive weight management program that includes diet and exercise, with careful consideration of potential side effects and contraindications, as suggested by the most recent guideline 1.

Key Considerations

• The recommended dosage of phentermine is 15 to 37.5 mg orally once daily in the morning, as stated in the study 1.
• Treatment should be initiated at the lower dose (15 mg) and increased gradually based on response and tolerability.
• Phentermine is approved for short-term use (usually up to 12 weeks), but many practitioners use it for a longer duration in an off-label fashion, as mentioned in the guideline 1.

Patient Selection and Monitoring

• Appropriate candidates for phentermine include patients with obesity who need assistance with appetite suppression, without contraindications such as heart disease, uncontrolled hypertension, hyperthyroidism, glaucoma, history of drug abuse, or pregnancy.
• Blood pressure and heart rate should be monitored regularly during treatment, as recommended in the guideline 1.

Lifestyle Modifications

• Patients should be counseled on lifestyle modifications including caloric restriction and increased physical activity alongside medication therapy, as part of a comprehensive weight management program.
• The medication works by stimulating the release of norepinephrine in the brain, which helps reduce hunger and increase feelings of fullness, as explained in the study 1.

Potential Side Effects and Dependence

• Common side effects include dry mouth, insomnia, constipation, and increased heart rate, as reported in the study 1.
• Phentermine should be discontinued gradually to avoid rebound effects, and it's essential to note that it has potential for dependence and is classified as a Schedule IV controlled substance.

From the FDA Drug Label

DOSAGE AND ADMINISTRATION Dosage should be individualized to obtain an adequate response with the lowest effective dose. The usual adult dose is 15 mg to 30 mg at approximately 2 hours after breakfast for appetite control. Late evening medication should be avoided because of the possibility of resulting insomnia Administration of one capsule (30 mg) daily has been found to be adequate in depression of the appetite for 12 to 14 hours. The recommended maximum dosage of phentermine hydrochloride is 15 mg daily for patients with severe renal impairments (eGFR 15 to 29 mL/min/1.73 m 2).

The proper dosing and prescription protocol for phentermine (Adipex-P) for weight loss is:

• Individualized dosage: to obtain an adequate response with the lowest effective dose
• Usual adult dose: 15 mg to 30 mg at approximately 2 hours after breakfast for appetite control
• Maximum dosage for severe renal impairment: 15 mg daily for patients with eGFR 15 to 29 mL/min/1.73 m 2
• Administration: one capsule (30 mg) daily, avoiding late evening medication to prevent insomnia 2, 2

From the Research

Phentermine Dosing and Prescription Protocol

• The proper dosing and prescription protocol for phentermine (Adipex-P) for weight loss varies depending on the study and patient population 3, 4, 5, 6, 7.
• In one study, phentermine was given at a dose of 8 mg twice per day (at 1:00 p.m. and 4:00 p.m.) in combination with fenfluramine 20 mg per day (at 4:00 p.m.) to target the eating patterns of obese subjects 3.
• Another study found that 30 mg phentermine was more effective than 15 mg phentermine in improving anthropometric variables in the 3-month follow-up, but not after completing the 6-month treatment period 4.
• A case study reported a patient who lost over 23 kg (13% of baseline peak weight) with a current weight of 153 kg and BMI of 54.4 kg/m2 after taking phentermine, initially at 15 mg daily and slowly up-titrated to 37.5 mg daily 5.
• A phase 3 trial found that the combination of phentermine and topiramate, with office-based lifestyle interventions, might be a valuable treatment for obesity, with patients achieving at least 5% weight loss 6.
• An open-label study of dose adjustment of fenfluramine and phentermine found that upward dose adjustment resulted in further weight loss in 11 and no gain in six participants 7.

Key Findings

• Phentermine doses have ranged from 15 to 37.5 mg per day in various studies 3, 4, 5, 7.
• The combination of phentermine and topiramate may be a valuable treatment for obesity, with patients achieving significant weight loss 6.
• Dose adjustment of phentermine and fenfluramine may be necessary to optimize response and minimize adverse effects 7.
• Phentermine may be effective in achieving short-term weight loss, with patients losing a mean of 22.4% of their initial weight over an average of 8.4 months 3.