Over-the-counter (OTC) medicines contain pharmacologically active substances havingdose-dependent efficacy. OTC medicines have smaller doses or packages than prescriptionmedicines containing the same drug. If the patient buys several packages of OTC medicine,then its usage might be prolonged and the doses consumed rise too high. A bigger riskcomes from OTC medicines having interactions with continuously or intermittently usedprescription medicines. Non-steroidal anti-inflammatory drugs could cause renal toxicitywith a simultaneous use of renin-angiotensin system inhibitors. Paracetamol at highdoses causes liver toxicity and increases the risks of anticoagulants. Simultaneoususe of aspirin and warfarin is contraindicated. The safety of OTC medicines has beenevaluated by authorities and deemed safe when used correctly.