The right amount of medicine separates help from harm. Dosage is the specification of how much drug is to be taken, how often, and for how long.

Dose depends on the drug’s properties, the patient’s age, weight, kidney and liver function, and the condition being treated. Too little yields no benefit; too much produces toxicity. Fixed-dose regimens suit many situations; others require titration according to response or blood levels.

Prescriptions and labels must state dosage clearly. Patients need instructions they can follow, including what to do if a dose is missed. In hospitals, computerized systems and double-checks reduce dosing errors. Revisiting dosage when clinical status changes prevents accumulation or under-treatment.

• Amount, frequency, and duration of a medication
• Adjusted for patient factors and clinical response
• Must be communicated clearly on prescriptions
• Errors in dosage are a major source of preventable harm