By far the major complaint with ECT is memory loss. Typically people undergoing ECT will lose their memory for events immediately preceding the treatments and for those during the series of ECT treatments. Some people may not remember much, or anything, of the weeks during which they were having multiple treatments. There have been numerous studies reporting that ECT does not cause permanent memory loss.
One recent study that looked at people six months after ECT argues against this, demonstrating ongoing problems with memory for things in the past (retrograde amnesia). This supports the experience of many people who have had ECT, often with very good results, who insist they’ve been left with residual memory difficulties. How the electrodes are placed on the head in ECT (unilateral vs. bilateral placement) show that unilateral may carry less risk of memory loss.
Other common complaints immediately following the treatment include nausea, headache, and muscle aches. These are readily treated with medication, and tend not to be severe. And finally, ECT can trigger a manic episode in someone who is depressed.