What are the contraindications for phentermine (Adipex-P) for weight loss?

Contraindications for Phentermine for Weight Loss

Phentermine is contraindicated in patients with cardiovascular disease, uncontrolled hypertension, hyperthyroidism, glaucoma, history of drug abuse, pregnancy, nursing, and in those taking monoamine oxidase inhibitors or within 14 days of their use. 1, 2

Absolute Contraindications

• Cardiovascular disease

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

• Uncontrolled hypertension 2, 1

  • Phentermine can increase blood pressure and heart rate

• Concurrent use of monoamine oxidase inhibitors (MAOIs) or within 14 days of discontinuation 1, 4

  • Risk of hypertensive crisis and potentially seizures

• Pregnancy and breastfeeding 1

  • Classified as pregnancy category X
  • Weight loss offers no benefit during pregnancy and may cause fetal harm
  • May be excreted in breast milk and cause adverse effects in nursing infants

• Hyperthyroidism 2, 4

  • Risk of arrhythmias and seizures

• Glaucoma (particularly angle-closure glaucoma) 4

• History of drug abuse 4, 1

  • Phentermine is a Schedule IV controlled substance with potential for abuse and dependence

Relative Contraindications/Use with Caution

• Renal impairment 1

  • Limit dosage to 15 mg daily in severe renal impairment (eGFR 15-29 mL/min/1.73 m²)
  • Avoid use in end-stage renal disease (eGFR <15 mL/min/1.73 m²)

• Diabetes mellitus requiring insulin or oral hypoglycemic medications 1

  • May require dose adjustment of antidiabetic medications

• Anxiety disorders 4

  • Phentermine may worsen anxiety symptoms

• Seizure disorders 4, 1

  • Increased risk of seizures

• Pediatric patients (under 16 years) 1

  • Safety and effectiveness not established

• Geriatric patients 1

  • Use with caution due to increased risk of decreased organ function

• Concomitant alcohol use 1

  • May result in adverse drug reactions

Clinical Considerations and Monitoring

1. Cardiovascular monitoring

   • Monitor blood pressure and heart rate every 2 weeks during the first 12 weeks 4
   • Discontinue if new or unexplained symptoms of dyspnea, angina pectoris, syncope, or lower extremity edema develop 1

2. Duration limitations

   • FDA-approved for short-term use only (≤12 weeks) 2, 4
   • Long-term use is off-label and lacks robust safety data 5

3. Potential adverse effects requiring monitoring

   • Cardiovascular: palpitations, tachycardia, elevated blood pressure 1
   • Neurological: overstimulation, restlessness, dizziness, insomnia 1
   • Gastrointestinal: dry mouth, constipation, diarrhea 1
   • Endocrine: changes in libido, impotence 1

Important Caveats

• Tolerance to the anorectic effect usually develops within a few weeks; if this occurs, phentermine should be discontinued 1
• Phentermine may impair the ability to operate machinery or drive 1
• When discontinuing phentermine, gradual tapering is recommended to minimize withdrawal effects 4
• Phentermine has been associated with rare but serious adverse events including ischemic colitis 6
• Phentermine is not recommended for use in combination with other weight loss medications unless specifically approved (e.g., phentermine-topiramate ER) 1, 7

By understanding these contraindications and monitoring requirements, healthcare providers can appropriately select patients for phentermine therapy and minimize potential risks while maximizing weight loss benefits.