According to a systematic review and network meta-analysis of 76 randomized controlled trials in adults who have recovered from depression with antidepressants, a combination of slow tapering and psychological support is as effective in preventing relapse as continuing treatment. Relapse rates were significantly higher when antidepressants were abruptly stopped or tapered rapidly. Most psychiatric diseases are highly polygenic, contrary to what was expected forty years ago after the identification of single-gene disorders such as Huntington's disease. Genome-wide data from more than one million people identified few disorder-specific loci. Genetic risk factors cross diagnostic boundaries, with significant overlap between schizophrenia and bipolar disorder, as well as depression, anxiety, and post-traumatic stress disorder. The article also mentions an increased incidence of Parkinson's disease in people on azathioprine, but details are not given.