- Taken any of the following substances: An investigational drug during the past four weeks; Metrifonate during the past three months; a drug or treatment known to cause major organ system toxicity during the past four weeks; other cholinergic drugs (e.g., donepezil, tacrine, succinylcholine-type muscle relaxants) during the past two weeks (topical pilocarpine will be permitted); antidepressant medication during the past four weeks.