There are four main in-patient drug distribution systems: individual prescriptions, complete floor stock, a combination of the two, and unit dose dispensing. Under floor stock systems, drugs are supplied to nursing stations and categorized as charge or non-charge floor stock. Charge drugs are billed directly to patients, while non-charge drugs are provided for all patients' use without individual billing. Unit dose systems package and distribute drugs in single doses for each patient. Centralized and decentralized models exist. Outpatients are non-admitted patients who visit the outpatient department for consultation and treatment as needed.