The effect of anticonvulsants and some psychotropic drugs on the conventional EEG.E. Ketz (Zurich, St. Gallen, Switzerland). Unexpected and undesired effects of the usual anticonvulusants on the scalp EEG are discussed. These findings need not correspond to clinical symptoms. They can. however. precede general signs of poisoning and therefore permit a prognosis of the compatbility of a drug. As regards the EEG monotherapies can be tolerated over many years without any side effects. Only after a second drug is added, disintegration of background activity. flattening of amplitude, lowering of frequencies and atypical drowsiness patterns, up to reactivation of hypersynchronous potentials may occur. Particularly unfavourable combinations of anticonvuisants in their effect on the EEG are demonstrated by some examples. EEG disturbances caused by anticonvulsants are probably dependent on the same factors as other. clinical, incompatibility reactions: individual sensitivity. dosage, elimination, cumuration, interference, incompatibility In 36 cases, the effects of some psychotropic drugs on the conventional EEG are presented. These were EEG recordings after taking hashish(marijuana), LSD, heroin, amphetamine and mescaline, solitary or in combination with alcohol, tranquilizers, analgesics or narcotics. Normal EEGs were only found in cases in which the use was given up a long time ago, even with previous chronic abuse. The EEG disturbances consisted of slight to moderate, diffuse alterations, with numerous atypical sleep patterns, but also with an increased frequency of the background activity. This was depenent on previous cerebral lesions, type of dug, duration and tme of consumption, dosage (often unknown), also on the cmbination with other medicaments or alcohol. Severe or characteristic EEG changes were not found.