What are the guidelines for using Adipex (phentermine) for weight loss?

Guidelines for Using Adipex (Phentermine) for Weight Loss

Phentermine (Adipex) is FDA-approved only for short-term use (up to 12 weeks) as an adjunct to diet and exercise for weight management in patients with a BMI ≥30 kg/m² or ≥27 kg/m² with weight-related comorbidities. 1

Indications and Patient Selection

• Indicated for patients with:

  • BMI ≥30 kg/m² or
  • BMI ≥27 kg/m² with risk factors (controlled hypertension, diabetes, hyperlipidemia) 1

• Not appropriate for patients with:

  • Cardiovascular disease
  • Uncontrolled hypertension
  • Hyperthyroidism
  • Glaucoma
  • Agitated states
  • History of drug abuse
  • Pregnancy or nursing
  • During or within 14 days of MAOI use 2, 3

Dosing Recommendations

• Available formulations:

  • Capsules: 15 mg, 30 mg, 37.5 mg
  • Tablets: 8 mg, 37.5 mg 3

• Standard dosing:

  • 15-37.5 mg once daily, preferably in the morning (to minimize insomnia)
  • Alternative: 8 mg tablets up to 3 times daily, approximately 30 minutes before meals 3, 2

• Titration approach:

  • Start with 15 mg daily
  • Adjust based on response and tolerability
  • Maximum dose: 37.5 mg daily 2

Monitoring and Follow-up

• Initial phase (first 3 months):

  • Monitor blood pressure and heart rate every 2 weeks 2
  • Assess efficacy and side effects monthly 2

• Efficacy assessment:

  • Discontinue if <5% weight loss achieved at 12 weeks 2
  • Expected weight loss: approximately 5-6% of body weight at 28 weeks 2

• Side effect monitoring:

  • Cardiovascular: blood pressure, heart rate, signs of pulmonary hypertension
  • Central nervous system: insomnia, irritability, dizziness
  • Gastrointestinal: dry mouth, constipation 3, 2

Duration of Treatment

• FDA approval is for short-term use only (up to 12 weeks) 1
• Off-label extended use requires:
  • Documentation of specific benefits
  • Assessment of tolerance and adverse effects
  • Patient counseling regarding limited data supporting long-term use 3
  • Regular monitoring of cardiovascular parameters 2

Common Side Effects

• Dry mouth, insomnia, dizziness, irritability
• Elevated heart rate and blood pressure
• Constipation, paresthesia
• Headache, diarrhea, esophageal reflux, abdominal pain 3, 2

Drug Interactions

• Contraindicated with monoamine oxidase inhibitors 3
• Use caution with:
  • Serotonergic drugs
  • Tramadol
  • Alcohol
  • Insulin or oral hypoglycemic medications (may require dose adjustment) 2, 4

Discontinuation

• When discontinuing after extended use, gradual tapering is recommended:
  • Week 1: Reduce to half dose (e.g., 18.75 mg daily)
  • Week 2: Further reduce to half dose every other day
  • Week 3: Discontinue completely 2

Important Considerations

• Phentermine is classified as a Schedule IV controlled substance due to potential for abuse and dependence 3
• Weight regain is common after discontinuation, highlighting the importance of lifestyle modifications 5
• Patients reporting greater baseline hunger and less dietary restraint may achieve better results with phentermine 6
• The historical combination of phentermine with fenfluramine ("fen-phen") was associated with serious valvular heart disease and is no longer used 3

Efficacy Expectations

• When used as monotherapy with lifestyle modifications, phentermine typically produces weight loss of 5-7% of initial body weight 2, 5
• Combination therapy with topiramate (available as Qsymia) may produce greater weight loss (8-10%) 7