Gabapentin causes drowsiness, dizziness, and coordination problems more than almost any other side effect, affecting roughly one in five people who take it. Beyond these well-known reactions, the drug can also cause swelling, weight gain, mood changes, and cognitive difficulties that many people don’t expect when they start treatment.
Dizziness, Drowsiness, and Coordination Problems
The three most common side effects of gabapentin are drowsiness, dizziness, and loss of coordination. In clinical trials for nerve pain, 28% of people taking gabapentin experienced dizziness (compared to 8% on placebo), and 21% experienced drowsiness (compared to 5% on placebo). In epilepsy trials, the numbers were slightly lower but still significant: 17% for dizziness and 19% for drowsiness.
Loss of coordination, sometimes called ataxia, affected 13% of epilepsy patients and 3% of nerve pain patients in those same trials. This can feel like unsteadiness on your feet, clumsiness, or difficulty with fine motor tasks. These effects are usually strongest when you first start the medication or after a dose increase, and they often improve over the first few weeks as your body adjusts.
Gabapentin works by binding to specific sites on calcium channels in the brain, which reduces the release of excitatory chemical signals. This calming effect is what makes it useful for seizures and nerve pain, but it’s also what makes you feel foggy, sleepy, or off-balance.
Swelling, Weight Gain, and Other Physical Effects
Swelling in the legs, ankles, or hands (peripheral edema) is a side effect that catches many people off guard. In nerve pain trials, 8% of people taking gabapentin developed noticeable swelling compared to just 2% on placebo. The rate was lower in epilepsy patients, around 2%. Other physical side effects reported in clinical trials include nausea, vomiting, diarrhea, constipation, dry mouth, tremor, fatigue, and double vision.
Weight gain is often a concern, though the data suggests it’s typically modest. In a long-term study lasting up to 24 weeks, patients gained an average of less than 1 kilogram (about 1.7 pounds). Some people gain more, especially at higher doses or over longer periods, but dramatic weight changes are not the norm for most users.
Mood Changes and Suicidal Thoughts
Gabapentin can affect your mental health in ways that aren’t always obvious. An analysis of the FDA’s adverse event reporting database found that about 12% of all reported gabapentin reactions involved psychiatric effects, including depression. Among those psychiatric reports, suicidal ideation was the most frequently reported event, accounting for nearly 23% of cases. Mood changes were also significantly overrepresented compared to what would be expected by chance.
This doesn’t mean gabapentin causes suicidal thoughts in 12% of people who take it. Adverse event databases capture reports, not rates, and they’re subject to reporting bias. But the signal is strong enough that the FDA requires all anti-seizure medications, including gabapentin, to carry warnings about the risk of suicidal behavior and ideation. If you notice worsening depression, unusual mood swings, or thoughts of self-harm after starting gabapentin, that’s worth bringing to your prescriber’s attention quickly.
Cognitive Effects Over Time
Many people describe a mental cloudiness on gabapentin, often called “brain fog.” Research supports this experience. In a controlled study of healthy adults, gabapentin significantly worsened attention, the ability to stay alert, and the speed of thinking and reacting. A small case series of spinal cord injury patients found measurable declines in memory, executive function, and attention after just one week on the drug.
For older adults, these cognitive effects may be more persistent. A study of people over 65 with normal cognition at baseline found that starting gabapentin was associated with a 55% higher chance of cognitive decline at the next clinical visit. By the second follow-up, there was also a significant increase in falls, with gabapentin users more than twice as likely to experience them. These findings don’t prove gabapentin directly caused the decline, but they reinforce that older adults should be monitored more closely.
Breathing Risks With Other Medications
In 2019, the FDA issued a safety warning that gabapentin can cause serious breathing problems, particularly in certain higher-risk groups. The people most at risk include those who take opioid pain medications at the same time, people with lung conditions like COPD, and older adults.
The concern is well supported. A large population-based study found that people taking both gabapentin and opioids had a 49% higher risk of dying from an opioid overdose compared to people taking opioids alone. At moderate to high gabapentin doses, the risk climbed to about 60% higher. At very high doses (2,500 mg daily or more), the risk nearly doubled. This happens because both drugs suppress the central nervous system, and the combined effect on breathing can become dangerous.
Withdrawal Symptoms When Stopping
Gabapentin can produce withdrawal symptoms if you stop it abruptly, even after a gradual taper. Symptoms can include anxiety, insomnia, nausea, sweating, and body pain. In severe cases, withdrawal can look remarkably similar to alcohol or benzodiazepine withdrawal, with agitation, confusion, rapid heartbeat, and elevated blood pressure.
One documented case involved a patient who developed severe mental status changes, chest pain, and high blood pressure 10 days after completing a week-long taper. The clinical recommendation is to taper gabapentin slowly, over weeks to months rather than days, following a schedule similar to what would be used for benzodiazepines. If you’ve been on gabapentin for more than a few weeks, stopping cold turkey is not advisable.
Higher Risks for Kidney Disease and Older Adults
Gabapentin is cleared almost entirely by the kidneys, which means people with reduced kidney function can accumulate the drug to toxic levels even at standard doses. In a study of patients with chronic kidney disease, toxicity occurred in nearly 78% of those on dialysis who received inappropriately high doses. Elderly patients with multiple health conditions were disproportionately affected.
The signs of gabapentin toxicity mirror the drug’s regular side effects but turned up to a dangerous level: extreme sedation, severe dizziness, slurred speech, and unresponsiveness. For anyone with known kidney problems, dosing needs to be adjusted based on how well the kidneys are filtering. This is something your prescriber should be calculating based on lab work, but it’s worth asking about if you know your kidney function is reduced.