Can gabapentin (Neurontin) cause weight gain?

Gabapentin and Weight Gain

Yes, gabapentin can cause weight gain as a side effect. This is clearly documented in the FDA drug label and multiple clinical guidelines.

Evidence for Weight Gain with Gabapentin

• The FDA drug label for gabapentin specifically lists "weight gain" as an adverse reaction that occurred in 2% of gabapentin-treated patients compared to 0% in placebo groups in postherpetic neuralgia trials 1
• Gabapentin is explicitly mentioned in clinical guidelines as one of the anticonvulsants associated with weight gain 2
• In a study of 44 patients on high-dose gabapentin therapy for 12+ months, 25 patients (57%) gained more than 5% of their baseline weight, with 10 patients (23%) gaining more than 10% of their baseline weight 3
• Weight gain typically begins between the second and third months of gabapentin treatment and tends to stabilize after 6-9 months 3

Mechanism and Risk Factors

• The exact mechanism of gabapentin-induced weight gain is not fully understood but may involve:

  • Effects on hypothalamic appetite regulation 4
  • Lowered blood glucose levels that may stimulate eating 4
  • Enhanced GABA-mediated neurotransmission that may increase appetite for carbohydrates 4

• Risk factors for greater weight gain may include:

  • Lower baseline weight/BMI 5
  • Higher doses (many patients experiencing significant weight gain were on doses >3000 mg/day) 3
  • Longer duration of treatment 3

Clinical Context and Comparison to Other Medications

• Gabapentin and pregabalin are considered first-line anticonvulsants for neuropathic pain, but their most bothersome side effects include somnolence, dizziness, and weight gain 2

• When comparing medications that may cause weight gain:

  • Antipsychotics (especially clozapine, olanzapine) generally cause more significant weight gain than gabapentin 6
  • Among antidepressants, paroxetine and mirtazapine are more associated with weight gain, while bupropion may cause modest weight loss 6
  • Among anticonvulsants, valproic acid typically causes more weight gain than gabapentin 4

Management Strategies

• For patients concerned about weight gain:

  • Consider alternative medications if clinically appropriate (e.g., topiramate has been associated with weight loss) 2
  • Monitor weight regularly, especially during the first 3-6 months of therapy 3
  • Implement lifestyle modifications including diet and exercise 2
  • Consider the lowest effective dose of gabapentin, as higher doses may be associated with greater weight gain 3

• For patients with diabetes or metabolic concerns:

  • Guidelines recommend minimizing medications associated with weight gain when treating patients with type 2 diabetes and obesity 2
  • Consider alternative medications with neutral or beneficial weight profiles when possible 2

Long-Term Effects

• In a study of gastroretentive gabapentin formulation used for 24 weeks, the mean weight change was modest at +0.76 kg, suggesting that weight gain may stabilize over time 7
• With pregabalin (a similar medication to gabapentin), the majority of patients (81.8%) remained within ±7% of baseline weight over 1 year of treatment 5

Weight gain is a documented side effect of gabapentin that should be discussed with patients before initiating therapy, particularly in those with existing weight concerns or metabolic conditions.