What are the side effects of gabapentin?

Gabapentin Side Effects

Most Common Side Effects

Gabapentin most commonly causes dizziness (17-28%), somnolence (14-21%), and peripheral edema (7-8%), with these effects typically improving significantly after the first week of treatment and largely resolving by week 4. 1, 2

Central Nervous System Effects

• Dizziness affects 17-28% of patients and is the most frequent CNS side effect 2
• Somnolence/drowsiness occurs in 14-21% of patients 2
• Ataxia (unsteadiness/coordination problems) develops in 13% of patients taking gabapentin for epilepsy 2
• Fatigue affects approximately 11% of patients 2
• Nystagmus (abnormal eye movements) occurs in 8% of patients 2
• Tremor is reported in 7% of patients 2
• Cognitive effects including abnormal thinking, amnesia, and difficulty with concentration occur in 2-3% of patients 2

Other Physical Side Effects

• Peripheral edema (leg/ankle swelling) affects 7-8% of patients 2
• Weight gain occurs in 2-3% of patients 1, 2
• Gastrointestinal effects including nausea (4%), diarrhea (6%), constipation (4%), dry mouth (5%), and vomiting (3%) 2
• Visual disturbances including blurred vision (amblyopia) in 3-4% and diplopia (double vision) in 6% of patients 2

Serious Side Effects

Suicidal Ideation

• Suicidal thoughts or behavior occur in approximately 1 in 500 patients (0.2%) 1, 2
• The FDA requires monitoring for new or worsening depression, anxiety, agitation, panic attacks, insomnia, irritability, hostility, impulsivity, or mania 2

Severe Allergic Reactions

• Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) is a potentially life-threatening allergic reaction that may affect skin, liver, or blood cells 2
• Warning signs include skin rash, hives, difficulty breathing, fever, swollen glands, facial/throat swelling, jaundice, unusual bruising/bleeding, severe fatigue, or frequent infections 2

Neuropsychiatric Effects in Children

• In pediatric patients ages 3-12 years, gabapentin causes emotional lability, aggressive behavior, hostility (8%), hyperactivity, concentration problems, and changes in school performance 2

Other Serious Effects

• Altered mental status requiring hospitalization occurs in approximately 1.27% of older adults (mean age 76) initiated on high doses (>600 mg/day) within 30 days 3
• Rhabdomyolysis (muscle breakdown) has been reported in postmarketing surveillance 2
• Respiratory depression and hypoventilation, particularly when combined with opioids 4

Dose-Related Considerations

• Side effects are typically dose-related, with higher incidence at doses above 1800 mg/day 1
• Approximately 10% of patients discontinue gabapentin due to side effects in clinical trials 1
• Slow titration starting at 300 mg/day (increasing to 600 mg on day 2, then 900 mg on day 3) minimizes adverse effects 1, 5
• Most side effects are mild to moderate and transient, improving markedly after the first week and largely resolving by week 4 1

Discontinuation and Withdrawal

• Adverse event withdrawals occur in 11% of gabapentin patients versus 8.2% on placebo 6
• Abrupt discontinuation can precipitate seizures (status epilepticus) in patients with epilepsy and should never be done without medical supervision 2
• Unlike some antidepressants, gabapentin does not have a withdrawal syndrome when tapered appropriately 1

Special Populations and Precautions

Renal Impairment

• Patients with kidney problems or on hemodialysis require dose adjustment due to reduced gabapentin clearance 1, 2

Drug Interactions

• Gabapentin has no significant drug interactions, does not inhibit CYP2D6, and does not induce liver enzymes 1
• Antacids containing aluminum and magnesium should be taken at least 2 hours before gabapentin to avoid reduced absorption 2
• Gabapentin may interact with morphine, caffeine, losartan, phenytoin, and magnesium oxide 4

Pregnancy and Breastfeeding

• Effects on unborn babies are unknown; patients should enroll in the North American Antiepileptic Drug Pregnancy Registry (1-888-233-2334) 2
• Gabapentin passes into breast milk 2

Contraindications

• Myasthenia gravis and myoclonus are contraindications to gabapentin use 4
• Known allergy to gabapentin or its ingredients 2

Common Pitfalls

• Combining gabapentin with alcohol or other CNS depressants significantly increases sedation and dizziness risk 2
• Driving or operating machinery should be avoided until individual response is known, as gabapentin slows thinking and motor skills 2
• In older adults, starting with high doses (>600 mg/day) increases the risk of altered mental status requiring hospitalization 3