What does a typical treatment cycle look like when prescribing Adipex (phentermine) to an adult patient with a body mass index (BMI) of 30 or higher, or 27 or higher with comorbidities such as diabetes or hypertension?

Adipex (Phentermine) Treatment Cycle

Adipex is FDA-approved only for short-term use of "a few weeks" (typically up to 12 weeks), though many practitioners use it for 3-6 months or longer off-label for chronic weight management, with continuation based on achieving at least 5% body weight loss and absence of cardiovascular contraindications. 1

Initial Dosing and Titration

• Start with 15 mg once daily, taken approximately 2 hours after breakfast, or use the lowest effective dose to minimize side effects 1
• Alternative low-dose regimen: 8 mg can be prescribed up to 3 times daily, particularly targeting afternoon/evening eating patterns 2, 3
• Avoid late evening administration due to risk of insomnia 1
• The standard dose range is 15-37.5 mg daily, with 30 mg daily providing appetite suppression for 12-14 hours 1

Pre-Treatment Requirements

Before prescribing, you must:

• Screen for cardiovascular disease history (coronary artery disease, stroke, arrhythmias, heart failure, uncontrolled hypertension) - these are absolute contraindications 4, 1
• Measure baseline blood pressure and heart rate 2
• Assess pregnancy status in women of reproductive potential and provide contraception counseling - pregnancy is an absolute contraindication 4, 1
• Screen for hyperthyroidism, glaucoma, agitated states, and history of drug abuse - all are contraindications 4, 1
• Verify no MAOI use within the past 14 days (risk of hypertensive crisis) 4, 1

Treatment Duration and Monitoring

FDA-Approved Duration

• Official approval is for "a few weeks" of use as short-term adjunct therapy 1

Real-World Off-Label Extended Use

• Many experienced clinicians use phentermine for 3-6 months or longer off-label because obesity is a chronic metabolic disease requiring long-term management 5, 2
• Clinical trial data supports 12-week cycles, with some studies extending to 26-28 weeks 5
• Decisions to continue beyond 12 weeks should be based on efficacy and safety, not arbitrary time limits 5

Mandatory Monitoring Throughout Treatment

• Monitor blood pressure and heart rate at every visit, especially in the first 12 weeks 5, 2
• Assess weight loss and tolerability monthly for the first 3 months, then at least every 3 months 6

Efficacy Benchmarks and Discontinuation Criteria

Discontinue phentermine if the patient has not lost at least 5% of body weight after 12 weeks on the maximum dose - continuing offers no benefit while exposing patients to cardiovascular and dependency risks 5, 2

Alternative benchmark:

• If 3% weight loss is not achieved after 12 weeks at standard dose, consider discontinuation or dose escalation 5

Special Dosing Considerations

Renal Impairment

• Maximum dose of 15 mg daily for patients with severe renal impairment (eGFR 15-29 mL/min/1.73 m²) 1
• Avoid use in patients with eGFR <15 mL/min/1.73 m² or end-stage renal disease requiring dialysis 1

Patients with Diabetes

• Insulin or oral hypoglycemic medication doses may require reduction during phentermine therapy 1

Critical Safety Warnings

Absolute Contraindications (Never Prescribe)

• Any history of cardiovascular disease (coronary artery disease, stroke, arrhythmias, congestive heart failure) 4, 1
• Uncontrolled hypertension 4, 1
• Current or recent (within 14 days) MAOI use 4, 1
• Hyperthyroidism 4, 1
• Glaucoma 4, 1
• Pregnancy or nursing 4, 1
• History of drug abuse 4, 1

Common Pitfalls to Avoid

• Do not confuse phentermine monotherapy with the discontinued "fen-phen" combination (phentermine-fenfluramine), which was associated with valvular heart disease and pulmonary hypertension - these risks were attributed to fenfluramine, not phentermine 2
• Do not combine with other weight loss medications - safety and efficacy of combination therapy has not been established 1
• Do not prescribe to patients with even mild hypertension without careful monitoring due to risk of blood pressure elevation 1

Documentation for Off-Label Extended Use

If prescribing beyond 12 weeks:

• Document specific benefits, tolerance profile, and adverse effects 2
• Counsel patients regarding off-label use and limited long-term safety data 2
• Ensure continued cardiovascular monitoring at every visit 2

When to Consider Alternatives

Phentermine should not be prescribed to patients with cardiovascular disease; safer alternatives include orlistat (lipase inhibitor with no sympathomimetic effects) 6, 2

For patients with type 2 diabetes, consider GLP-1 analogues (such as liraglutide or semaglutide) that reduce hyperglycemia in addition to promoting weight loss 6