Some anticonvulsants cause significant weight gain, but the effect varies dramatically depending on which medication you take. Valproate, gabapentin, and pregabalin are the most likely to add pounds, while others like lamotrigine and levetiracetam are weight-neutral, and topiramate can actually cause weight loss. Understanding which drugs fall into which category can help you have a more informed conversation about your treatment options.
Which Anticonvulsants Cause Weight Gain
Valproate (sold as Depakote, Depakene, and other brands) carries the highest risk. About 57% of adults and 58% of older children and teenagers gain weight on it, with an average gain of around 6 kilograms (about 13 pounds). That weight gain becomes noticeable as early as 10 weeks into treatment and, unlike many medication side effects, does not plateau. Studies tracking patients on valproate for four or more years found weight continuing to climb the entire time.
Gabapentin is another common culprit. A meta-analysis found an average gain of 2.2 kg (roughly 5 pounds) in just six weeks, and an open-label study reported that 57% of patients with seizures gained at least 5% of their body weight. The effect appears dose-dependent: in one trial of patients with nerve pain, only those on higher doses (2,400 mg and 3,600 mg daily) had statistically significant increases.
Pregabalin follows a similar pattern. In a multicenter trial, 11.4% of patients on pregabalin gained 7% or more of their body weight, compared to just 3.1% on placebo. Like gabapentin, the weight gain tends to increase with higher doses. Carbamazepine and vigabatrin have also been linked to weight gain, though typically less dramatically than valproate.
Which Anticonvulsants Are Weight-Neutral or Cause Weight Loss
Lamotrigine is one of the most reliably weight-neutral options. In a head-to-head study against valproate, patients on lamotrigine maintained stable weight over an eight-month treatment period while the valproate group gained steadily. Levetiracetam and phenytoin are also generally weight-neutral, with some smaller studies suggesting levetiracetam may even produce modest weight reduction. Felbamate has been associated with slight weight loss as well.
Topiramate stands out as the anticonvulsant most likely to cause weight loss. Large randomized trials in adults have shown average losses of up to 10% of starting body weight. In adolescents, one study documented a 4.9% drop in BMI over six months. Zonisamide has a similar, though less studied, effect, with one retrospective study showing BMI reductions of 3.2 to 6.1 points every six months in people who started with a BMI of 25 or higher. The weight loss effect of topiramate is well enough established that a combination version (with phentermine) is approved specifically as a weight-loss medication.
Why These Drugs Affect Weight
The mechanisms differ from drug to drug, and researchers still don’t have a complete picture. For medications that promote weight gain, one pathway involves blood sugar. Some anticonvulsants lower blood glucose by interfering with how the body processes fatty acids. When blood sugar drops, the hypothalamus, your brain’s appetite control center, gets a signal to eat. The result is increased hunger, particularly for carbohydrates.
Another mechanism involves the brain chemical GABA. Drugs that boost GABA activity can simultaneously increase appetite and reduce energy expenditure, a combination that makes weight gain almost inevitable over time. Some anticonvulsants may also cause a deficiency in carnitine, a molecule your body needs to burn fat for energy. When carnitine drops, your body burns more glucose instead of fat, which again drives hunger. Less commonly, effects on hormones that regulate water retention or on brain chemicals like serotonin and norepinephrine may play a role.
Topiramate works in the opposite direction. It suppresses appetite through two routes: boosting GABA’s inhibitory signals in appetite-regulating brain areas and blocking glutamate, a stimulating brain chemical that normally promotes food intake when it acts on the hypothalamus. Topiramate also appears to reduce levels of neuropeptide Y, one of the body’s most powerful appetite stimulators.
Who Is Most at Risk
Not everyone on a weight-promoting anticonvulsant will gain the same amount. Women tend to gain more weight than men on valproate. Post-pubertal adolescents are more susceptible than younger children. And people who are already overweight before starting treatment are more likely to experience further gains. Longer treatment duration also increases the total amount of weight gained, with the most significant accumulation typically occurring during the first year, though gains can continue well beyond that point.
Dose matters too. The gabapentin and pregabalin data both show dose-dependent effects, meaning higher doses carry a greater risk of noticeable weight change. This is worth knowing because these medications are sometimes prescribed across a wide dosage range depending on the condition being treated.
Managing Weight on These Medications
The most effective strategy is choosing a weight-neutral or weight-loss-associated anticonvulsant from the start, when that’s medically appropriate. For someone already overweight, a drug like topiramate may offer a dual benefit, while valproate or gabapentin could worsen an existing problem. This is a conversation worth having with your prescriber before filling the first prescription.
If you’re already on a weight-promoting anticonvulsant and it’s working well for your condition, switching isn’t always practical. In that case, tracking your weight weekly gives you early warning. Clinical guidelines suggest that a gain of more than 5 pounds should prompt a reassessment of whether a medication change makes sense. Paying attention to appetite shifts is equally important, since many of these drugs increase hunger before the scale moves.
Dietary awareness helps, particularly around carbohydrate cravings, which are a direct side effect of the GABA and blood sugar mechanisms described above. Recognizing that the urge to snack may be pharmacologically driven rather than a reflection of genuine energy needs can make it easier to respond with a plan rather than on autopilot. Some patients benefit from working with a behavioral psychologist to develop strategies for managing medication-driven appetite changes, especially when food becomes a go-to response to stress or boredom.
Quick Comparison by Drug
- Valproate: highest risk, ~57% of patients affected, average gain ~6 kg, no plateau over time
- Gabapentin: moderate to high risk, dose-dependent, ~2.2 kg average gain in 6 weeks
- Pregabalin: moderate risk, dose-dependent, up to 11% of patients gain 7%+ body weight
- Carbamazepine: modest risk of weight gain
- Vigabatrin: modest risk of weight gain
- Lamotrigine: weight-neutral
- Levetiracetam: weight-neutral, possibly slight loss
- Phenytoin: weight-neutral
- Topiramate: weight loss up to 10% of body weight
- Zonisamide: weight loss, less extensively studied
- Felbamate: slight weight loss