What are the contraindications to phentermine (Adipex-P)?

Contraindications to Phentermine (Adipex-P)

Phentermine is contraindicated in patients with cardiovascular disease, uncontrolled hypertension, hyperthyroidism, glaucoma, agitated states, history of drug abuse, during or within 14 days of MAOI use, pregnancy, nursing, and known hypersensitivity to sympathomimetic amines. 1, 2

Absolute Contraindications

• Cardiovascular disease:

  • History of coronary artery disease
  • Heart failure
  • Stroke
  • Arrhythmias (including atrial fibrillation) 3
  • Valvular heart disease 1
  • Uncontrolled hypertension 2

• Drug interactions:

  • Use during or within 14 days following administration of monoamine oxidase inhibitors (MAOIs) due to risk of hypertensive crisis 1, 2
  • Caution with serotonergic medications due to potential for serotonin syndrome 4

• Endocrine/metabolic conditions:

  • Untreated hyperthyroidism (risk of arrhythmias and seizures) 2

• Ophthalmologic conditions:

  • Glaucoma (risk of acute angle-closure glaucoma) 1, 2

• Psychiatric conditions:

  • Agitated states
  • History of drug abuse 1

• Pregnancy and lactation:

  • Pregnancy (Category X) - may result in fetal harm 1
  • Nursing mothers - amphetamines are present in human milk 1

• Hypersensitivity:

  • Known hypersensitivity to sympathomimetic amines 1

Relative Contraindications and Cautions

• Renal impairment:

  • Severe renal impairment (eGFR 15-29 mL/min/1.73m²): limit dose to 15mg daily
  • End-stage renal disease (eGFR <15 mL/min/1.73m²) or requiring dialysis: avoid use 1

• Geriatric patients:

  • Use with caution due to decreased renal function and increased risk of adverse effects 1
  • Start at lower doses and monitor renal function 1

• Concomitant medication use:

  • Alcohol (may result in adverse drug reactions) 1
  • Insulin and oral hypoglycemic medications (may require dose adjustments) 1, 2
  • Adrenergic neuron blocking drugs (may decrease hypotensive effect) 1
  • Tramadol (severe drug-drug interaction potential) 4

• Pediatric patients:

  • Safety and effectiveness not established 1
  • Not recommended for chronic treatment of pediatric obesity 1

Clinical Considerations

• Phentermine is only FDA-approved for short-term use (≤12 weeks) 2
• Monitor blood pressure and heart rate regularly, especially during the first 12 weeks of treatment 5
• Discontinue if tolerance develops to the anorectic effect 1
• Consider potential for abuse and dependence due to chemical and pharmacological similarity to amphetamines 1
• May impair ability to operate machinery or drive 1

Common Adverse Effects

• Cardiovascular: palpitations, tachycardia, elevated blood pressure 2
• Central nervous system: restlessness, dizziness, insomnia, euphoria, dysphoria, tremor, headache 1
• Gastrointestinal: dry mouth, unpleasant taste, diarrhea, constipation 2, 1

When prescribing phentermine, a thorough cardiovascular risk assessment is essential, as even mild hypertension warrants caution due to the potential for blood pressure elevation 1. The medication should be discontinued immediately if cardiovascular symptoms develop, including unexplained dyspnea, angina, syncope, or lower extremity edema 5.