Identifying genes in which variation influences susceptibility to adverse drug reactions has the obvious value for genetic testing before starting a drug treatment and might also make it easier to screen molecules likely to cause adverse drug reactions at an early stage of the drug development process. Thus, increased knowledge about genetic causes of adverse drug reactions can minimise the risk with drug treatment in the future. Another possibility is the development of drugs targeted at mechanisms involved in adverse drug reactions, e.g., mechanisms involved in weight gain due to neuroleptics and antidepressants may aid the development of drugs for the treatment of obesity.