The most serious side effects of gabapentin include respiratory depression (dangerously slowed breathing), suicidal thoughts and behavior, a severe allergic reaction called DRESS syndrome, and heightened overdose risk when combined with opioids. While gabapentin is generally well tolerated at appropriate doses, these rare but potentially life-threatening effects prompted the FDA to add new safety warnings in 2019.
Respiratory Depression
Gabapentin can slow breathing to dangerous levels, particularly in people who already have compromised lung function. In December 2019, the FDA required new warnings on all gabapentin prescribing information after identifying cases of serious breathing difficulties. The people most vulnerable include those with chronic obstructive pulmonary disease (COPD) or other conditions that reduce lung function, people taking opioids or other sedating medications, those with kidney impairment, and older adults.
The risk escalates significantly when gabapentin is combined with opioid painkillers. An Ontario population study found that patients co-prescribed gabapentin and opioids were 49% more likely to die from an opioid-related cause than patients taking opioids alone. At moderate to high doses of gabapentin, that figure climbed to nearly 60%. This happens because both drugs suppress the central nervous system, and the combined effect on breathing can be greater than either drug alone.
If you take gabapentin alongside any sedating medication, watch for excessive drowsiness, unusually slow or shallow breathing, confusion, or blue-tinged lips or fingertips. These signs warrant immediate medical attention.
Suicidal Thoughts and Behavior
Gabapentin carries an increased risk of suicidal ideation and behavior. A large Swedish population study covering 2006 to 2013 found that 5.2% of people prescribed gabapentinoids presented with suicidal behavior or died by suicide during the study period. Using a design where each person served as their own comparison, researchers found a 26% increase in suicidal behavior during periods when people were taking gabapentinoids versus periods when they were not.
Age matters substantially. The highest risk appeared in people aged 15 to 24, where the hazard was 67% higher during treatment periods. Adults under 55 also showed elevated risk. For people 55 and older, the association was weaker or absent. These findings don’t mean gabapentin directly causes suicidal behavior in every case, but they do signal that mood changes during treatment should be taken seriously, especially in younger patients.
DRESS Syndrome
Drug Reaction with Eosinophilia and Systemic Symptoms, known as DRESS syndrome, is a rare but potentially fatal allergic reaction that gabapentin can trigger. Unlike a typical drug rash that appears within days, DRESS has an unusually long delay: it typically develops 2 to 6 weeks after starting the medication, which makes it easy to miss the connection.
The first sign is usually a high fever, present in 80% to 90% of cases. This is followed by a widespread, itchy rash covering more than half the body. Facial swelling occurs in roughly three-quarters of patients. Swollen lymph nodes appear in 30% to 50% of adults. What makes DRESS dangerous is that it doesn’t stop at the skin. It causes inflammation of internal organs, most commonly the liver, but sometimes the lungs and heart as well. Each of these features (rash, fever, blood abnormalities, organ involvement) is present in over 90% of confirmed cases. Symptoms can persist even after stopping the drug.
Cognitive Decline and Falls in Older Adults
For people over 65, gabapentin poses distinct neurological risks. A study of older adults who started with normal cognitive function found that gabapentin use was associated with a 55% higher odds of measurable cognitive decline at one year and a roughly doubled odds on a more detailed cognitive assessment. By the two-year mark, the risk of falls had increased 2.5 times compared to non-use.
In hospitalized surgical patients, those who received gabapentin before a fall were nearly twice as likely to have been taking the drug compared to patients who did not fall. Confusion, unsteady gait, and excessive sedation are the mechanisms behind these numbers. Because older adults are also more likely to have reduced kidney function (which slows gabapentin clearance from the body), the drug can accumulate to higher levels than intended, amplifying these effects.
Kidney Impairment and Drug Buildup
Gabapentin is eliminated almost entirely through the kidneys. When kidney function declines, the drug builds up in the body, increasing the intensity of every side effect. Dose reductions are necessary at specific thresholds of kidney function. Someone with moderately reduced kidney function (roughly half of normal filtering capacity) needs about half the standard dose. A person with severely reduced function may need as little as one-tenth of the typical dose.
Because kidney function naturally declines with age, many older adults require lower doses even if they’ve never been diagnosed with kidney disease. Toxicity from drug accumulation can present as extreme drowsiness, confusion, difficulty breathing, or muscle weakness, and it can develop gradually over days or weeks as levels rise.
Peripheral Edema
Swelling in the legs, ankles, and feet affects 2% to 8% of people taking gabapentin, with higher rates at higher doses. This edema can be alarming because it mimics the appearance of heart failure, and there are documented cases of patients being treated aggressively for heart failure that turned out to be entirely caused by gabapentin. One important distinction: unlike fluid retention from heart or kidney problems, gabapentin-induced swelling does not respond to diuretics (water pills). If you develop new leg swelling while on gabapentin, the drug itself should be considered as a possible cause before pursuing more invasive cardiac workups.
Withdrawal Risks
Stopping gabapentin abruptly can trigger withdrawal symptoms within 12 hours to 7 days, including anxiety, insomnia, nausea, sweating, and pain. The most serious withdrawal risk is seizures, which can occur even in people who were not taking gabapentin for epilepsy. Withdrawal episodes typically last 5 to 10 days, though some people require up to 18 weeks of gradual tapering to discontinue the medication safely.
The risk of withdrawal seizures is highest with abrupt cessation after prolonged use or high doses. A slow, supervised taper is the standard approach to discontinuation regardless of why you were prescribed the drug.
Pregnancy Concerns
Among pregnancies exposed to gabapentin during the first trimester, major birth defects occurred in about 5 out of every 100 live births, with cardiac malformations specifically affecting about 1.9 per 100. After adjusting for other factors, the overall risk of major malformations was only slightly higher than the general population rate and was not statistically significant. Still, the data remains limited, and the potential for harm means gabapentin use during pregnancy requires careful weighing of benefits against risks, particularly for women taking it for pain rather than seizure control.