What is the recommended starting dose of phentermine (phentermine) for adults?

Phentermine Starting Dose Recommendations

The recommended starting dose of phentermine for adults is 15 mg to 30 mg taken once daily, approximately 2 hours after breakfast for appetite control. 1

Dosing Guidelines

• The FDA-approved dosing for phentermine should be individualized to obtain adequate response with the lowest effective dose:
  • Standard starting dose: 15-30 mg once daily, taken approximately 2 hours after breakfast 1
  • Administration timing: Morning dosing is recommended (avoid late evening dosing due to insomnia risk) 1
  • Duration: Short-term use only (a few weeks) as an adjunct to diet and lifestyle modification 1, 2

Patient Selection Criteria

Phentermine is indicated for patients with:

• BMI ≥30 kg/m² (without comorbidities) OR
• BMI ≥27 kg/m² with weight-related comorbidities (e.g., hypertension, diabetes, hyperlipidemia) 2

Dosage Adjustments

• Renal impairment: Maximum 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

Monitoring Recommendations

• Blood pressure and heart rate should be monitored every 2 weeks during the first 12 weeks
• Efficacy and safety assessment at least monthly for the first 3 months 2

Important Precautions

• Phentermine is contraindicated in patients with:
  • Cardiovascular disease
  • During or within 14 days of MAO inhibitor use
  • Hyperthyroidism
  • Glaucoma
  • Agitated states
  • History of drug abuse
  • Pregnancy or nursing
  • Hypersensitivity to sympathomimetic amines 1
  • History of seizure disorders or epilepsy 2
  • Age under 16 years 2, 1

Expected Outcomes

• Modest weight loss (approximately 3.6 kg at 6 months)
• Average weight loss of 5-6% of body weight at 28 weeks 2
• Weight regain commonly occurs after medication discontinuation 2

Common Adverse Effects

• Dry mouth (most common)
• Insomnia
• Dizziness
• Irritability
• Headache
• Elevated blood pressure and heart rate
• Constipation
• Anxiety 2

Discontinuation

When stopping 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 2

Remember that phentermine is only approved for short-term use (a few weeks) and should always be used as an adjunct to diet, exercise, and behavioral modification for optimal weight management outcomes.