Gabapentin, sold under brand names like Neurontin, is an anticonvulsant medication primarily prescribed to manage partial seizures and relieve nerve pain [1.4.2, 1.4.5]. Although it was designed as a structural analog of the neurotransmitter GABA, its exact mechanism of action involves binding to specific subunits of voltage-gated calcium channels, which reduces the release of excitatory neurotransmitters in the brain [1.5.1, 1.5.5]. Its use has become widespread for both FDA-approved and off-label conditions, including restless legs syndrome, fibromyalgia, and anxiety [1.4.1, 1.4.4].
While many people tolerate gabapentin well, it is associated with a range of potential side effects [1.4.5]. Understanding these effects is crucial for anyone taking the medication.
The Biggest and Most Common Side Effects
The most consistently reported and widespread side effects of gabapentin are central nervous system (CNS) related, specifically dizziness and somnolence (sleepiness or drowsiness) [1.2.4].
- Dizziness: This is often cited as the number one side effect. In clinical studies for postherpetic neuralgia, dizziness affected up to 28% of patients taking gabapentin, compared to just 8% on a placebo [1.2.2]. For epilepsy, the incidence was around 17% [1.2.2]. This can lead to unsteadiness, a higher risk of falls, and difficulty with coordination (ataxia) [1.3.1, 1.9.3].
- Somnolence/Drowsiness: Feeling sleepy or fatigued is also very common, affecting about 21% of patients in some studies [1.2.2]. This side effect can significantly impair a person's ability to drive or operate heavy machinery, prompting warnings from health authorities [1.2.2, 1.3.6].
These two side effects are often most intense when starting the medication or after a dose increase and may lessen over time as the body adjusts [1.3.2].
Other Common Adverse Reactions
Beyond dizziness and drowsiness, several other side effects are frequently reported. In clinical trials, common reactions (affecting 1% to 10% or more of users) included [1.2.1, 1.2.3, 1.9.1]:
- Ataxia: Poor muscle control and clumsiness, affecting up to 13% of users [1.2.1, 1.2.3].
- Fatigue and Asthenia: A general feeling of tiredness, weakness, or lack of energy [1.2.1].
- Peripheral Edema: Swelling in the hands, feet, or lower legs [1.2.1].
- Nystagmus: Uncontrolled, repetitive eye movements [1.2.2].
- Visual Disturbances: Blurred or double vision (diplopia) [1.2.1, 1.3.2].
- Gastrointestinal Issues: Nausea, vomiting, constipation, or diarrhea [1.3.4].
- Weight Gain: Can result from increased appetite or metabolic changes [1.3.2, 1.9.3].
Serious and Long-Term Side Effects
Though less common, gabapentin is associated with serious risks that require immediate medical attention.
- Respiratory Depression: The FDA has issued a warning about the risk of serious, potentially fatal breathing problems, especially when gabapentin is taken with other CNS depressants like opioids, alcohol, or benzodiazepines, or by elderly patients and those with underlying respiratory conditions like COPD [1.2.2, 1.8.2, 1.9.5].
- Suicidal Thoughts and Behavior: Like other antiepileptic drugs, gabapentin carries an increased risk of suicidal ideation and behavior in a small number of people (about 1 in 500) [1.3.6, 1.9.5]. Patients and caregivers should monitor for new or worsening depression, anxiety, or any unusual changes in mood or behavior [1.2.2].
- Anaphylaxis and Angioedema: Severe allergic reactions, though rare, can occur. Symptoms include swelling of the lips, throat, and tongue, and difficulty breathing, which requires emergency treatment [1.2.2, 1.3.2].
- DRESS Syndrome: A rare but life-threatening drug reaction with symptoms like fever, rash, and swollen lymph nodes that can lead to organ damage [1.2.5].
- Dependence and Withdrawal: Long-term use can lead to physical dependence. Suddenly stopping gabapentin can cause withdrawal symptoms like anxiety, insomnia, nausea, pain, sweating, and seizures [1.7.1, 1.7.2, 1.7.3]. A gradual tapering of the dose under medical supervision is essential [1.3.6].
- Cognitive and Mood Changes: Long-term use has been linked to memory problems, difficulty concentrating, confusion, and mood changes like depression or anxiety [1.9.3]. In children, it can cause hostility, emotional lability, and hyperactivity [1.2.2].
Comparison with Pregabalin (Lyrica)
Pregabalin is a similar medication, often called a "sister drug" to gabapentin. While their side effect profiles are largely the same (dizziness, drowsiness), there are some differences. Pregabalin is absorbed more quickly and predictably by the body [1.6.4]. Some studies suggest pregabalin might be more likely to cause weight gain unrelated to fluid buildup, while gabapentin is linked more to ataxia and diarrhea [1.6.4, 1.6.1].
| Feature | Gabapentin | Pregabalin |
|---|---|---|
| Most Common Side Effects | Dizziness, Somnolence (Drowsiness), Ataxia [1.2.1, 1.2.2] | Dizziness, Somnolence (Drowsiness), Headache [1.6.1, 1.6.5] |
| Absorption | Saturable, bioavailability decreases with higher doses [1.5.3] | Faster and more predictable absorption [1.6.4] |
| Other Notable Side Effects | More likely to cause ataxia and diarrhea [1.6.1] | More likely to cause weight gain (unrelated to fluid) and headache [1.6.4, 1.6.5] |
| Controlled Substance Status | Controlled in several states, but not federally in the U.S. [1.7.2] | Federally classified as a Schedule V controlled substance in the U.S. [1.6.4] |
Conclusion
The biggest and most frequent side effects of gabapentin are dizziness and drowsiness, which can impair coordination and daily functioning. While many adverse effects are mild and transient, there are significant risks, including severe respiratory depression (especially with opioids), mood changes, and physical dependence leading to withdrawal. Patients should never stop taking gabapentin abruptly and must consult their healthcare provider to manage side effects and create a safe treatment plan. An authoritative source for further reading is the National Institutes of Health's MedlinePlus page on Gabapentin [1.4.3].
