Question: when is a drug studied in patients who have the condition that the drug is intended to treat
Answer: clinical researcher 100 -- 300 patients with specific diseases approximately 33 % determines whether drug can have any efficacy ; at this point , the drug is not presumed to have any therapeutic effect whatsoever Phase III Testing of drug on patients to assess efficacy , effectiveness and safety therapeutic dose clinical researcher and personal physician 300 -- 3,000 patients with specific diseases 25 -- 30 % determines a drug 's therapeutic effect ; at this point , the drug is presumed to have some effect Phase IV Postmarketing surveillance -- watching drug use in public therapeutic dose personal physician anyone seeking treatment from their physician N / A watch drug 's long - term effects