The first real long-term study wasn't done until 2007(!) and memory and cognitive problems were still present at six months, the neurological time threshold that establishes permanent damage. Ironically, the man who led the study was the same person who created the oft-repeated "only 1/200 suffer side effects" line that is repeated in every article or documentary ever produced...
" Something most remarkable and unexpected has occurred in the field of psychiatry. Lead by a lifelong defender and promoter of shock treatment, Harold Sackeim, a team of investigators has recently published a follow up study of 347 patients given the currently available methods of electroshock, including the supposedly most benign forms--and confirmed that electroshock causes permanent brain damage and dysfunction.
Based on numerous standardized psychological tests, six months after the last ECT every form of the treatment was found to cause lasting memory and mental dysfunction. In the summary words of the investigators, "Thus, adverse cognitive effects were detected six months following the acute treatment course." They concluded, "this study provides the first evidence in a large, prospective sample that adverse cognitive effects can persist for an extended period, and that they characterize routine treatment with ECT in community settings."
After traumatic brain damage has persisted for six months, it is likely to remain stable or even to grow worse. Therefore, the study confirms that routine clinical use of ECT causes permanent damage to the brain and its mental faculties..."
http://www.huffingtonpost.com/dr-peter-breggin/disturbing-news-for-patie_b_44734.html