This method is considered safe: the death rate due to this treatment is estimated as 4 case per 100,000 treatments, and the benefits, when given to the right patients seems to justify it - depression may be severe enough to result in self harm.
However, there are side effects - the procedure itself may cause a short seizure, and some disturbances with the heart rhythm. Therefore, the patient is usually monitored during the therapy.
ECT may also cause memory loss that usually resolves within weeks. and also disorientation, fatigue, nausea, and muscle aches.
Although this list may be frightening, as I said, it's considered a good and helpful treatment.
You may read more here:
http://www.nlm.nih.gov/medlineplus/ency/article/0033...