What are the side effects of gabapentin?

Gabapentin Side Effects

Most Common Side Effects

Gabapentin most commonly causes dizziness, somnolence (drowsiness), and peripheral edema, with these effects occurring significantly more frequently than placebo in clinical trials. 1

Central Nervous System Effects

• Dizziness occurs in 17-28% of patients taking gabapentin compared to 7-8% on placebo 1
• Somnolence affects 19-21% of patients versus 5-9% on placebo 1
• Ataxia (unsteadiness/coordination problems) develops in 13% of patients versus 6% on placebo 1
• Fatigue occurs in 11% of patients compared to 5% on placebo 1
• Other CNS effects include tremor (7%), dysarthria (2%), amnesia (2%), and abnormal thinking (2%) 1

Other Common Side Effects

• Peripheral edema occurs in 8% of patients with postherpetic neuralgia versus 2% on placebo 1
• Nystagmus (abnormal eye movements) affects 8% of patients versus 4% on placebo 1
• Diplopia (double vision) occurs in 6% versus 2% on placebo 1
• Weight gain develops in 2-3% of patients 2, 1
• Gastrointestinal effects include dry mouth (5%), diarrhea (6%), constipation (4%), and nausea (4%) 1

Serious Side Effects

Suicidal Thoughts and Behavior

• Suicidal thoughts or actions occur in approximately 1 in 500 patients (0.2%) taking antiepileptic drugs including gabapentin 3, 1
• Patients should be monitored for new or worsening depression, anxiety, agitation, panic attacks, insomnia, irritability, aggressive behavior, or mania 1

Severe Allergic Reactions

• Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) and other serious allergic reactions can occur, potentially affecting skin, liver, or blood cells 1
• Warning signs include skin rash, hives, difficulty breathing, fever, swollen glands, facial/throat swelling, jaundice, unusual bruising/bleeding, severe fatigue, or unexpected muscle pain 1

Altered Mental Status

• Gabapentin is associated with hospitalization for altered mental status, particularly at higher doses 4, 5
• The risk increases in a dose-dependent manner, with highest risk at doses ≥2,400 mg/day 4
• Older adults (mean age 76 years) initiated on high doses (>600 mg/day) have a 1.29-fold increased risk of hospitalization with altered mental status compared to low doses (≤600 mg/day) 5

Falls and Fractures

• Gabapentin increases the risk of falls or fractures with an incidence of 1.81 per 100 person-years versus 1.34 per 100 person-years in unexposed patients (relative risk 1.35) 4
• Clear dose-response relationship exists, with highest risk at doses ≥2,400 mg/day (relative risk 1.90) 4

Dose-Related Considerations

• Side effects are typically dose-related, with higher incidence at doses above 1,800 mg/day 3
• Approximately 10% of patients discontinue gabapentin due to side effects in clinical trials for neuropathic pain 3
• Slow titration starting at 300 mg/day and gradually increasing can minimize side effects 3
• In clinical trials for postherpetic neuralgia, 16% of gabapentin patients discontinued versus 9% on placebo 1

Special Populations and Situations

Pediatric Patients (Ages 3-12)

• Behavioral and emotional changes are prominent in children, including emotional lability, aggressive behavior, hostility, problems with concentration, restlessness, changes in school performance, and hyperactivity 1
• Viral infection (11%), fever (10%), and nausea/vomiting (8%) occur more frequently in pediatric patients 1

Renal Impairment

• Patients with kidney problems or on hemodialysis require dose adjustment due to reduced clearance of gabapentin 3, 1

Drug Interactions

• Gabapentin has no known significant drug interactions and does not inhibit liver enzymes, unlike many other medications 2, 6
• Antacids containing aluminum and magnesium should be taken at least 2 hours before gabapentin 1

Rare but Documented Side Effects

• Hypoglycemia has been reported, even in patients without diabetes, potentially due to effects on pancreatic calcium channels 7
• Rhabdomyolysis (muscle breakdown) has been reported in postmarketing surveillance 1
• Hyponatremia (low sodium) has been documented 1
• Sexual dysfunction including changes in libido, ejaculation disorders, impotence (2%), and anorgasmia 1

Clinical Management Pearls

• Unlike opioids, tolerance does not develop to most side effects of gabapentin 3
• Side effects in menopausal symptom management (dizziness, unsteadiness, drowsiness) affect up to 20% but markedly improve after the first week and are largely resolved by week 4 2
• Abrupt discontinuation can cause serious problems including status epilepticus in epilepsy patients 1
• Gabapentin can impair driving ability and motor skills; patients should avoid operating heavy machinery until they know how the medication affects them 1