Effects of psychotropic drugs on EEG

All drugs used in psychiatry might induce CNS toxicity, particularly when polypharmacy is required for management of patients. Toxic effects can occur at therapeutic doses when concomitant medical conditions or treatments interfere with drug metabolism and/or cause a potentiation of CNS toxicity, for example in old subjects treated with lithium a delirium due to encephalopathy can be precipitated by renal failure, deydration following diuretics or adjunctive neuroleptic therapy. A standard EEG (sEEG) investigation may be useful to diagnose an encephalopathic process, which will be documented by diffuse slowing or the presence of triphasic waves, or an epileptic condition, indexed by spike and spike-and-wave potentials. Data indicating the usefulness of sEEG for the diagnosis of drug-induced CNS side effects or toxicity are summarized and discussed for antipsychotics, antidepressants, anxiolytics, lithium, other mood stabilizers and recreational drugs. A case vignette of SEEG usefulness in diagnosing drug-induced toxic encephalopathy is provided.