- For patients treated with anticholinergics and/or benzodiazepines, they must be willing and safely able to abstain from any of these medication for a period of at least 5 plasma half-lives of the individual drug prior to study participation (2 days for trihexyphenidyl which has a plasma half life around 4 hours; 12 days, for clonazepam which has a half-life of 18-50 hours).