ABSTRACT:The effects of drugs on the EEG have been of interest since Berger demonstrated in 1929 that electrical signals could be recorded from the scalp. Berger described changes in the EEG following a variety of medications and, based on these observations, hypothesized that there was a relationship between changes in alpha activity and mental processes. A large number of drugs have now been demonstrated to alter the EEG and many of these drug-induced changes may be clinically useful. Understanding the effects and significance of drug effects on the EEG requires an understanding of the physiological basis of electroencephalography. This paper reviews the physiological basis of the EEG and the effects of commonly used drugs on background rhythms and epileptiform activity. The effects of prenatal and postnatal drug exposure on the neonatal EEG are also reviewed.