What are the risks associated with using phentermine (anorexiant) for weight loss?

Risks of Phentermine for Weight Loss

Phentermine is approved only for short-term use (≤12 weeks) due to significant safety concerns including cardiovascular risks, potential for abuse, and numerous contraindications. 1, 2

Major Safety Concerns

Cardiovascular Risks

• Primary pulmonary hypertension (PPH) - rare but potentially fatal lung disease 2
• Valvular heart disease affecting mitral, aortic, and tricuspid valves 2
• Increased heart rate and blood pressure 1, 3
• Palpitations, tachycardia, and potential ischemic events 2
• Contraindicated in patients with history of heart disease or uncontrolled hypertension 1, 3

Neurological and Psychiatric Effects

• Central nervous system effects: insomnia, restlessness, dizziness, anxiety, euphoria, dysphoria, tremor, headache 2
• Potential for psychosis in susceptible individuals 2
• May impair ability to operate machinery or drive vehicles 2
• Depression and anxiety-related adverse events 4

Dependence and Abuse Potential

• Chemically and pharmacologically related to amphetamine 2
• Risk of tolerance development requiring discontinuation 2
• Potential for abuse and dependence requiring careful monitoring 2, 5
• Withdrawal symptoms may occur with abrupt discontinuation 3

Contraindications

• Pregnancy and breastfeeding (Category X) 2
• Glaucoma 1, 3
• Hyperthyroidism 1, 3
• Anxiety disorders or agitated states 1
• History of drug abuse 1, 3
• Use with MAO inhibitors (or within 14 days) 1, 3, 2
• Seizure disorders 1

Common Side Effects

• Dry mouth (reported in up to 21% of patients) 4
• Constipation (up to 17%) 4
• Insomnia (up to 10%) 4
• Dizziness (up to 10%) 4
• Dysgeusia (altered taste) (up to 10%) 4
• Gastrointestinal disturbances 2
• Paresthesia 4

Drug Interactions

• Severe interactions with MAO inhibitors (risk of hypertensive crisis) 2
• Concomitant use with alcohol may result in adverse reactions 2
• May decrease effectiveness of adrenergic neuron blocking drugs 2
• May require dose adjustment of insulin or oral hypoglycemic medications 2
• Potential severe interactions with tramadol (reported in 46.79% of long-term users) 6
• Moderate interactions with multiple commonly prescribed medications 6
• Risk when combined with serotonergic drugs 2

Monitoring Requirements

• Blood pressure and heart rate should be monitored every 2 weeks during the first 12 weeks 3
• Efficacy and safety assessment at least monthly for the first 3 months 3
• Regular monitoring of metabolic parameters in diabetic patients 2

Important Considerations

1. FDA approval is for short-term use only (≤12 weeks) 1, 2
2. When discontinuing, gradual tapering is recommended to minimize withdrawal effects 3
3. Long-term safety data is limited, creating concerns about chronic use 7
4. Newer weight loss medications with better safety profiles may be preferable for long-term management 3

Alternative Weight Management Options

For patients with contraindications to phentermine, alternatives include:

• GLP-1 receptor agonists (liraglutide, semaglutide) 3
• Orlistat (works through non-sympathomimetic mechanism) 3
• Naltrexone/bupropion (with appropriate precautions) 1

While phentermine can produce significant weight loss (3.6 kg more than placebo in short-term studies) 1, the numerous safety concerns and contraindications make it suitable only for carefully selected patients without cardiovascular risk factors, and only for short-term use.