Phentermine Use Protocol
Phentermine should be used only as a short-term adjunct (maximum 12 weeks) to diet and lifestyle modification for weight reduction in patients with BMI ≥30 kg/m² or ≥27 kg/m² with risk factors, with careful monitoring of cardiovascular parameters. 1, 2
Indications and Patient Selection
- Indicated for adults with:
- BMI ≥30 kg/m², or
- BMI ≥27 kg/m² with risk factors (e.g., controlled hypertension, diabetes, hyperlipidemia) 2
- Contraindicated in patients with:
- History of cardiovascular disease (coronary artery disease, stroke, arrhythmias, heart failure, uncontrolled hypertension)
- Hyperthyroidism
- Glaucoma
- Agitated states
- History of drug abuse
- Pregnancy or breastfeeding
- Use of MAO inhibitors (current or within past 14 days)
- Primary pulmonary hypertension
- Anxiety disorders
- Seizure disorders
- Age <16 years 1, 2
Dosing and Administration
- Standard dosing:
- 15-37.5 mg once daily (standard formulation) or
- 8 mg three times daily (Lomaira) 1
- Timing:
- Administer approximately 2 hours after breakfast
- Avoid late evening administration due to risk of insomnia 2
- Special populations:
- Severe renal impairment (eGFR 15-29 mL/min/1.73m²): Maximum 15 mg daily
- Avoid use in end-stage renal disease (eGFR <15 mL/min/1.73m²) 2
Monitoring Protocol
Initial assessment:
- Baseline blood pressure and heart rate
- Review of contraindications and drug interactions
Ongoing monitoring:
- Blood pressure and heart rate every 2 weeks during first 12 weeks
- Efficacy and safety assessment at least monthly for first 3 months 1
- Monitor for potential drug interactions, especially with serotonergic drugs, MAO inhibitors, and stimulants
- Adjust insulin or oral hypoglycemic medications in diabetic patients as needed 1, 2
Treatment Duration
- FDA approval is for short-term use only (12 weeks or less) 1
- The limited long-term safety data and potential cardiovascular risks make extended use inadvisable 1
Discontinuation
- When discontinuing phentermine, gradual tapering is recommended:
- Week 1: Half the regular dose daily
- Week 2: Half the regular dose every other day
- Week 3: Complete discontinuation 1
Common Side Effects
- Headache
- Elevated blood pressure and heart rate
- Insomnia
- Dry mouth
- Constipation
- Anxiety 1
Important Considerations and Pitfalls
- Avoid combination with other weight loss medications, as safety and efficacy of such combinations are not established 2
- Monitor for primary pulmonary hypertension, a rare but serious potential complication 2
- Tolerance to the anorectic effect typically develops within a few weeks; if this occurs, phentermine should be discontinued rather than increasing the dose 2
- Phentermine may impair ability to operate machinery or drive 2
- For long-term weight management, newer options like GLP-1 receptor agonists (semaglutide, tirzepatide) may be preferred due to greater efficacy and safety data 1
- Patients with cardiovascular disease should avoid phentermine; semaglutide is preferred in these cases 1
While some research has explored extended use of phentermine or its use in adolescents, the official protocol remains limited to short-term use in adults due to safety concerns and limited long-term efficacy data 1, 2.