(I) Most people believe that some drugs are acceptable and even desirable because of the medical benefits they confer. (II) But all psychoactive drugs – drugs that cross the blood-brain barrier and alter mental functioning – are potentially harmful to health. (III) Even drugs that are not psychoactive have the potential for unpleasant side effects. (IV) For a time, cocaine was used as an anaesthetic for surgery, especially eye surgery. (V) For example, antihistamines may cause confusion, dizziness, dry mouth and blurred vision.