The most common side effects of gabapentin in dogs are sedation and ataxia, a wobbly, uncoordinated gait that can make your dog look almost drunk. These effects are usually most noticeable in the first few days of treatment and tend to fade as your dog adjusts to the medication. While gabapentin is generally well tolerated, there are less common reactions and important safety considerations worth knowing about, especially if your dog takes other medications or has kidney or liver problems.
Sedation and Loss of Coordination
Drowsiness is the side effect you’re most likely to notice. Your dog may sleep more than usual, seem less interested in play, or respond more slowly to commands. Alongside this, many dogs develop ataxia, where they stumble, sway, or have trouble navigating stairs and slippery floors. These two effects often show up together because gabapentin works by reducing the activity of certain calcium channels in the nervous system, which dampens nerve signaling throughout the body.
The good news is that most dogs become tolerant to the sedation and coordination issues within a few days, especially when the dose starts low and increases gradually. Gabapentin takes effect within one to two hours of being given, and its effects wear off relatively quickly in healthy dogs, which is why it’s typically dosed two to three times per day. If your dog still seems overly sedated after the first week, the dose may simply be too high.
Less Common Side Effects
Beyond sedation and wobbliness, some dogs experience gastrointestinal symptoms like vomiting, nausea (look for lip-licking or reduced interest in food), or signs of abdominal pain such as a hunched posture or looking at their belly. A retrospective study from the Swedish University of Agricultural Sciences documented a broader range of possible reactions during the first two weeks of treatment, including fatigue, depression, nervousness, tremors, muscle twitches, and dizziness.
Behavioral changes deserve special attention. In that same study, two out of 16 dogs (12.5%) had to stop gabapentin entirely because of adverse effects, and both became noticeably depressed shortly after starting the medication. The Swedish Medical Products Agency also received a report of aggression in a Rottweiler on gabapentin between 2010 and 2017. These behavioral shifts are uncommon, but if your dog’s personality changes significantly after starting the drug, that’s worth flagging to your vet.
Risks for Dogs With Kidney or Liver Disease
Gabapentin is cleared from the body primarily through the kidneys. In dogs with chronic kidney disease, the drug lingers longer in the bloodstream, which means side effects like sedation and ataxia can be more pronounced and last longer. Veterinarians typically cut the starting dose in half and space it out more for dogs with significant kidney impairment. A dog that would normally start at 10 to 20 mg/kg every 8 to 12 hours might instead begin at 5 to 10 mg/kg once or twice daily.
Liver function matters too. In dogs, gabapentin undergoes some processing in the liver, which creates a theoretical risk of liver stress when combined with other medications that are hard on the liver, such as phenobarbital. This is especially relevant because many dogs on gabapentin for seizures are also taking phenobarbital. If your dog is on both, your vet may want to monitor liver values periodically.
Drug Interactions to Watch For
Two categories of medications interact with gabapentin in meaningful ways. Antacids can interfere with gabapentin’s absorption, potentially making it less effective. If your dog takes an antacid, spacing the two medications apart can help. Opioid pain medications like hydrocodone or morphine can alter how gabapentin is processed in the body and may amplify its sedative effects, making your dog significantly drowsier than either drug would alone.
Any sedating medication combined with gabapentin has the potential to stack sedation. If your dog is already on a medication that causes drowsiness, the combined effect can be stronger than you’d expect from either drug individually.
The Xylitol Danger in Liquid Formulations
This is one of the most important safety issues with gabapentin for dogs, and it has nothing to do with gabapentin itself. Some human liquid formulations of gabapentin contain xylitol, an artificial sweetener that is extremely toxic to dogs. When a dog ingests xylitol, it triggers a massive release of insulin that can crash blood sugar levels within 10 to 60 minutes. Symptoms include vomiting, weakness, staggering, collapse, and seizures. Untreated, it can be fatal.
If your vet prescribes a liquid form of gabapentin, make sure it’s a veterinary formulation or a compounded version made specifically for animals. Always check the ingredient label. Capsules and tablets don’t carry this risk.
What Happens if You Stop Gabapentin Suddenly
Gabapentin should not be stopped abruptly, especially in dogs taking it for seizure control. Because it’s a short-acting drug, sudden withdrawal can trigger rebound seizures. The standard approach is a gradual taper, with dose reductions every one to two weeks. Even in dogs using gabapentin for pain or anxiety rather than epilepsy, tapering is the safer route. If you need to discontinue the medication, your vet can outline a schedule that minimizes withdrawal risks.
Signs of Overdose
There is no established toxic dose of gabapentin in dogs, which means the exact amount that becomes dangerous isn’t clearly defined. What’s known is that dogs receiving higher-than-normal therapeutic doses develop exaggerated versions of the usual side effects: heavy sedation, pronounced ataxia, lethargy, and vomiting. If your dog accidentally gets into a bottle of gabapentin or receives a double dose, the primary concerns are severe sedation and the risk of aspiration if vomiting occurs while the dog is too drowsy to protect their airway. Contact your vet or an animal poison control center if you suspect an overdose.