[Controlling drug activity with light: developments in photopharmacology].

For millennia, humanity has been fascinated by the prospect of using visible light in medical applications. Nowadays, light is used in the clinic for intraoperative imaging and photodynamic therapy, among others. However, the precision of light delivery has also the potential to enable safe and targeted pharmacological treatments. This is the dream behind the emerging field of photopharmacology, which develops drugs whose activity can be regulated with light irradiation. Those photopharmacological drugs can be designed in two ways. Firstly, the drug can be "silenced" by attachment of a group that can be locally removed with light. Secondly, a molecular photoswitch can be inserted into a drug molecule to enable it switching on and off with different colours of light. In this article, a perspective is given on the basic principles and future of photopharmacology on its way to clinical applications.