Does methadone cause weight loss?

Methadone and Weight Changes

Methadone typically causes weight gain rather than weight loss, with significant increases in BMI occurring especially during the first year of treatment.

Evidence on Methadone and Weight

The FDA drug label for methadone specifically lists "weight gain" as a metabolic and nutritional adverse effect that may occur during treatment 1. This is the most authoritative source on methadone's effects on body weight.

Multiple research studies confirm this weight-gaining effect:

• A longitudinal study found that BMI increased significantly from 22.5 to 24.4 during initial methadone maintenance treatment (MMT), and continued to increase to 25.6 once patients were stabilized 2.

• Body composition analysis revealed that methadone treatment is associated with:

  • Increased BMI
  • Increased percentage of body fat
  • Increased average body mass
  • Increased basal metabolic rate
  • Relative decrease in percentage of muscle mass and bone mass 3

• Another four-year longitudinal study showed that weight gain occurs primarily in the first year of treatment (significant BMI increase from 22.2 to 24.7), with smaller increases in the second year, after which weight tends to stabilize 4.

Pattern and Timing of Weight Changes

The weight gain pattern with methadone follows a specific timeline:

1. First year: Most significant weight gain occurs
2. Second year: Some additional but less significant weight gain
3. Years 3-4: Weight typically stabilizes with no further significant increases 4

This pattern suggests that methadone-associated weight gain represents a normalization process rather than a continuous adverse effect. Before entering treatment, many opioid-dependent individuals are undernourished, with 10% being underweight 5. After one year of methadone treatment, the percentage of underweight patients decreases to 5%, while the percentage of overweight patients increases from 15% to 29% 5.

Risk Factors for Weight Gain

Interestingly, certain factors predict greater weight gain during methadone treatment:

• Hepatitis C virus seronegative status
• Absence of benzodiazepine abuse at admission
• Lower knowledge about healthy diet
• Higher preference for sweet foods 2

Clinical Implications

For clinicians managing patients on methadone:

• Monitor weight regularly, especially during the first year of treatment
• Provide nutritional education and counseling at treatment initiation
• Consider recommending dietary and lifestyle modifications to improve overall health 3
• Be aware that weight gain appears to be independent of methadone dosage and blood levels 2

While weight gain (not weight loss) is the expected outcome with methadone treatment, this should be viewed in context of the overall benefits of methadone maintenance therapy for opioid use disorder, including reduced mortality and improved quality of life 6.