The claim that aspartame is associated with an increased risk of epilepsy is based on the anecdotal reports of individuals who happened to experience their first seizure soon after consuming an aspartame-containing food or beverage. This is not evidence of causation, but a temporal relationship between the widespread consumption of aspartame and the prevalence of epilepsy. Epileptogenesis can be promoted by a variety of factors including stress, hydration, changes in plasma osmolarity and toxic metabolites resulting from hepatic or renal overload. Administration of large doses of water alone can predispose a person to seizures. The sharing on the Internet of the misinterpreted cause of a seizure episode or epilepsy due to aspartame, and inappropriate advice to avoid it, puts affected individuals at risk if they do not seek medical attention.
A review of studies by Butchko et al. on the effects of phenylalanine and aspartame in nine seizure models, ranging from chemical to genetic models including rodents and primates, found dosage levels below 1,000 mg/kg did not have effects on seizure susceptibility in animals. That is equivalent to an oral bolus of 18 cans of aspartame-sweetened diet soda by a 70 kg man. Results from dosage levels of aspartame at 1,000 mg/kg were inconsistent between laboratories, different seizure models and animals, showing either no effect or a proconvulsant effect. The data from these excessive bolus doses of aspartame in rodents do not suggest relevant risk to people since it is not possible for a person to orally ingest sufficient amounts of any aspartame-containing food or beverage to reach equivalent doses or raise plasma phenylalanine concentrations to comparable levels.
Consumers who believe they may have had an aspartame-related seizure or onset of epilepsy can be referred to this statement from The Epilepsy Institute published in the Congressional Record on June 20, 1986:
“As an organization devoted to people with seizure-related problems, we [at] the Epilepsy Institute have evaluated the current scientific evidence and found aspartame to be safe for people with epilepsy. . . . the members of the Professional Advisory Board of the Epilepsy Institute looked at the seizure activity of our patients, many of whom consume aspartame regularly, and saw no change over the past three years.”