Gabapentin causes drowsiness, dizziness, and fatigue in a significant number of people who take it. These are the most frequently reported side effects, but the drug can also affect mood, weight, breathing, and long-term cognitive function depending on your dose, age, and other medications. Here’s what to expect and what to watch for.
Common Side Effects
The side effects most people notice when starting gabapentin are neurological: drowsiness, dizziness, and a general feeling of fatigue or fogginess. These tend to be strongest in the first few weeks as your body adjusts to the medication. Coordination problems, blurred or double vision, and unsteadiness are also common early on. Many people describe it as feeling slightly “off balance” or mentally sluggish.
Digestive issues show up frequently too. Nausea, diarrhea, and dry mouth are reported at higher rates than with placebo in clinical trials. Some people experience swelling in the hands, feet, or lower legs, which results from fluid retention rather than true weight gain, though the two can overlap.
Weight Gain
Weight gain is real but modest for most people. In clinical trials, about 3% of adults with epilepsy gained weight on gabapentin compared to 2% on placebo. For people taking it for nerve pain after shingles, the rate was about 2%. Those who do gain weight typically put on around 5 pounds after six weeks of use. It’s not dramatic for most, but it can be frustrating if you’re already managing your weight carefully, and some people gain more over longer periods.
Mood Changes and Suicidal Thoughts
Gabapentin carries a class-wide warning for all anti-seizure medications regarding suicidal thoughts and behavior. A large Swedish study tracking nearly 192,000 people prescribed gabapentinoids found that treatment periods were associated with a 26% increase in suicidal behavior or death from suicide compared to periods when the same individuals were off the medication.
Age matters considerably here. The strongest link appeared in people aged 15 to 24, where the risk was 67% higher during treatment. Adults under 55 showed elevated risk, while those 55 and older showed little or no increased risk. When researchers separated gabapentin from pregabalin (a related drug), gabapentin alone showed weaker or no statistically significant associations with most of these outcomes, suggesting pregabalin may drive much of the signal. Still, the possibility is worth taking seriously, especially for younger users.
Watch for new or worsening depression, anxiety, agitation, irritability, restlessness, or any thoughts of self-harm. These changes can be subtle at first, so it helps to ask people close to you to flag any shifts they notice in your mood or behavior.
Breathing Problems
The FDA issued a specific warning about serious breathing difficulties in people taking gabapentin, particularly those with additional risk factors. These include taking opioid painkillers or other sedating medications (benzodiazepines, certain antidepressants, sleep aids, antihistamines), having a lung condition like COPD, and being elderly.
This is not a theoretical concern. Among 49 cases of respiratory depression reported to the FDA over a five-year period, 12 people died. Every one of those deaths involved at least one risk factor, most commonly the combination of gabapentin with another sedating drug. The mechanism is straightforward: gabapentin slows activity in the central nervous system, and stacking it with other drugs that do the same thing can suppress the brain’s drive to breathe.
Warning signs of respiratory depression include unusual confusion, extreme sleepiness you can’t shake off, shallow or slow breathing, and bluish discoloration of the lips or fingertips. If you take gabapentin alongside an opioid or any other sedating medication, these symptoms need immediate medical attention.
Cognitive Effects With Long-Term Use
Short-term brain fog is well known with gabapentin, but recent research raises questions about longer-term cognitive effects. A retrospective study found that people who received six or more gabapentin prescriptions were 29% more likely to be diagnosed with dementia and 85% more likely to be diagnosed with mild cognitive impairment within 10 years, compared to similar patients not prescribed the drug.
The risk was not spread evenly across age groups. Adults aged 18 to 34 showed no increased risk. But among those aged 35 to 49, the risk of dementia more than doubled and mild cognitive impairment more than tripled. A similar pattern held for people aged 50 to 64. Risk also climbed with prescription frequency: patients with 12 or more prescriptions were 40% more likely to develop dementia than those with fewer prescriptions.
This study was retrospective, meaning it looked backward through medical records rather than following patients prospectively. The researchers couldn’t account for actual doses or how long each prescription lasted. So while the pattern is concerning enough to warrant monitoring, it doesn’t prove gabapentin directly causes cognitive decline. People prescribed gabapentin more frequently may also have more severe underlying pain conditions or other factors that independently affect brain health.
Kidney Function and Drug Buildup
Gabapentin is cleared almost entirely by the kidneys, which means it can accumulate to toxic levels in people with reduced kidney function. This is one of the more important practical considerations, because many people taking gabapentin for nerve pain are older adults whose kidney function may be declining without obvious symptoms.
When gabapentin builds up in the body, the typical side effects become amplified: severe drowsiness, confusion, and involuntary muscle jerking. The good news is that these toxicity symptoms are usually reversible once levels come back down. But the required dose reductions are dramatic. Someone with moderately impaired kidneys may need less than a quarter of the standard maximum dose. If you’re on gabapentin and your kidney function changes for any reason (dehydration, a new medication, aging), your dose may need adjustment.
Withdrawal Effects
Stopping gabapentin abruptly after regular use can trigger withdrawal symptoms including anxiety, insomnia, nausea, sweating, and in people who take it for epilepsy, increased seizure frequency. These effects can begin within 12 hours to 7 days after the last dose. Tapering gradually over at least a week, and often longer, helps avoid this rebound. Even if you’re taking gabapentin for pain rather than seizures, stopping suddenly is not recommended.