Electroconvulsive therapy: A procedure in which an electric current is passed through the brain to produce controlled convulsions (seizures) to treat patients with depression, particularly for those who cannot take or are not responding to antidepressants, have severe depression, or are at high risk for suicide. Electroconvulsive therapy (ECT) is believed to act by a massive neurochemical release in the brain due to the controlled seizure. The most common side effect is short-term memory loss, which usually resolves quickly. ECT typically relieves depression within 1 to 2 weeks after beginning treatments.