*3.1.5 Photochemical degradation*

These are the reactions that take place by absorption of the visible or ultraviolet light. The reactant molecule absorbs photons of light (energy) and get excited. The excited molecule then produces the photodecomposition product.

In many photochemical reactions, the reactant molecule may not absorb the radiation directly but through a mediator which absorbs the incident radiation and subsequently transfers its energy to the reactant molecule that becomes activated. Such type of mediator is called photosensitizer.

At times, a molecule can act as a protector for the photolabile drug by preferentially absorbing the radiant energy and produce products. These compounds are referred to as screening agents [9].
