What are the most common side effects of gabapentin (Neurontin)?

Most Common Side Effects of Gabapentin

The most common side effects of gabapentin are dizziness, somnolence (drowsiness), and peripheral edema (swelling). 1 These central nervous system and fluid-related effects occur frequently in patients taking this medication and should be anticipated when initiating therapy.

Primary Side Effect Profile

According to FDA drug labeling data, the most common adverse reactions in controlled trials include:

Nervous System Effects

• Dizziness (28%) - occurs in more than 1 in 4 patients 1
• Somnolence/drowsiness (21%) - affects approximately 1 in 5 patients 1
• Ataxia (3%) - unsteady movements and poor coordination 1
• Abnormal thinking (3%) 1
• Abnormal gait (2%) 1
• Incoordination (2%) 1

Gastrointestinal Effects

• Dry mouth (5%) 1
• Diarrhea (6%) 1
• Constipation (4%) 1
• Nausea (4%) 1
• Vomiting (3%) 1

Metabolic Effects

• Peripheral edema (8%) - swelling, typically in the extremities 1
• Weight gain (2%) 1

Visual Effects

• Blurred vision (3%) - reported as amblyopia in clinical trials 1
• Diplopia (double vision) (1%) 1

Discontinuation Rates

In clinical trials for postherpetic neuralgia, approximately 16% of patients discontinued gabapentin due to adverse effects, compared to 9% in the placebo group 1. The most common reasons for discontinuation were dizziness, somnolence, and nausea 1.

Special Considerations

Elderly Patients

Older patients may be more sensitive to the central nervous system effects of gabapentin, particularly dizziness and somnolence, which can increase fall risk 2.

Renal Impairment

Gabapentin is primarily eliminated through renal excretion. In patients with impaired renal function:

• Dose adjustment is required 2
• Accumulation can lead to increased side effects and potentially serious toxicity 2, 3
• Rare cases of rhabdomyolysis (muscle breakdown) have been reported in patients with renal dysfunction 3, 4

Drug Interactions

When combined with other CNS depressants (including opioids), gabapentin may increase sedation and dizziness 1. This combination requires careful monitoring and potential dose adjustment.

Serious but Less Common Side Effects

While not among the most common, clinicians should be aware of these potentially serious adverse effects:

• DRESS syndrome (Drug Reaction with Eosinophilia and Systemic Symptoms) 1
• Suicidal behavior and ideation - requires monitoring for mood changes 1
• Withdrawal seizures if discontinued abruptly 1
• Anaphylaxis and angioedema - rare but potentially life-threatening 1

Patient Counseling Points

• Side effects are often dose-related and may be minimized with slower titration 5
• Many side effects are transient and may improve with continued therapy 5
• Patients should be advised not to drive or operate machinery until they know how gabapentin affects them 1
• Abrupt discontinuation should be avoided due to risk of withdrawal symptoms 1

In summary, while gabapentin is an effective medication for neuropathic pain conditions and epilepsy, the central nervous system effects (dizziness and somnolence) along with peripheral edema represent the most common side effect burden that patients and clinicians should anticipate.