A very controversial treatment, first used in 1938 to treat schizophrenia and widespread during the 1940s.
Psychiatrists used ECT for all sorts of disorders including alcoholism, personality disorders, and eating disorders. It is now considered inappropriate for these disorders and schizophrenia.
ECT is used very rarely now. Successful drug treatments have emerged since the 1950s.
A weak current is passed across the temples for 0.5 - 4 seconds.
The patient's body goes into convulsions that are reduced by muscle relaxants and anaesthetic (a mouth gag prevents the tongue being bitten).
Oxygen is given before and after treatment to aid recovery.
Therapy usually consists of a series of shock treatments over several weeks.
ECT may seem brutal but it seems to benefit some people with acute depression when other treatments have not worked.
No one really knows what ECT does to the brain or why it sometimes has a positive effect on severely depressed people.
ECT might work by altering the person's memory or by chemically changing their brain's functioning.
The side effects of ECT are not fully understood. Not surprisingly, the patient suffers confusion and muscular aches afterwards. Memory can also be affected.
When it was first used, some patients died in ECT due to undetected heart defects - patients are now screened carefully before the treatment is allowed.
Many people have objected to the use of ECT because we do not fully understand the effects of it. Critics have said it's a bit like kicking a television, or hitting a computer, to make it work.