that might occur only rarely. this type of analysis is also used in establishing chemical residue tolerances in foods. maximum tolerated dose studies are also done in clinical trials. mtd is an essential aspect of a drug's profile. all modern healthcare systems dictate a maximum safe dose for each drug, and generally have numerous safeguards (e.g. insurance quantity limits and government-enforced maximum quantity/time-frame limits) to prevent the prescription and dispensing of quantities exceeding the highest dosage which has been demonstrated to be safe for members of the general patient population. patients are often unable to tolerate the theoretical mtd of a drug due to the occurrence of side-effects which are not innately a manifestation of toxicity (not considered to severely threaten a patient's health) but cause the patient sufficient distress and/or discomfort to result in non-compliance with treatment. such examples include emotional "blunting" with antidepressants, pruritus with opiates, and blurred vision with anticholinergics.