Some chemical compounds are so powerful that they will cause seizures in most of those exposed. War gas which has actually been used in some units to induce seizures in those with severe depression as an alternative to electroconvulsive therapy. In this case the seizure is the required effect, but in all other instances seizures complicating drug therapy are very much an unwanted effect.
Antidepressant drugs of the tricyclic group, including amitryptiline (for example, Tryptizol, Saroten, Domical) and nortryptyline (for example, Allegron, Aventyl) are amongst those which clearly lower the convulsive threshold and precipitate seizures. Other offenders include phenothiazines, isoniazid, and high doses of penicillin. Excessive doses of insulin precipitate seizures through hypoglycaemia (low blood sugar). Any of these drugs may precipitate a first seizure or exacerbate established epilepsy.
Finally, it should be remembered that withdrawal of some drugs, particularly barbiturates, may precipitate seizures.