Concepts of 'Efficacy' and 'Safety'

The concept of efficacy and safety of a medicine refers to the ability of a treatment to work while causing no unnecessary harm.

• This means that the benefit of taking a medicine, despite potential side effects, is higher than the risk of leaving the condition untreated.
• To phrase it differently a medicine is beneficial when it produces the desired effect (efficacy) with a suitably low chance of side effects (safety).

This is also known as the ‘benefit-risk relationship’ (or benefit-risk ratio, it was previously known as the risk-benefit ratio/relationship).