###HUMAN: Count the number of patients on a main drug type prescription with diagnoses icd9 code 41512., ###ASSISTANT: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id INNER JOIN prescriptions ON demographic.hadm_id = prescriptions.hadm_id WHERE diagnoses.icd9_code = "41512" AND prescriptions.drug_type = "MAIN"