Hyperammonemic encephalopathy was reported by Katano Hiroyuki of the Nagoya City Higashi General Hospital in early 2002 in a patient who had been stable on primidone monotherapy for five years before undergoing surgery for astrocytoma, a type of brain tumor. Additionally, her phenobarbital levels were inexplicably elevated post-surgery. This is much more common with the valproates than with any of the barbiturates. A randomized controlled trial whose results were published in the July 1985 issue of "The New England Journal of Medicine" found that primidone was more likely to cause impotence than phenytoin, carbamazepine, or phenobarbital. Like phenytoin, primidone is rarely associated with lymphadenopathy. Primidone can also cause vomiting; this happens in 1.0–0.1% of users.