Adverse effects

Drugs efficiently alleviate symptoms and cure diseases. However, drugs are not always as selective as one would wish for. This poses a problem, as lacking drug selectivity leads to adverse effects in the organism it was administered. Selectivity in this context means that the drug only acts on a certain defined target (e.g. the origin of let’s say head ache) and not on any other targets (e.g. stomach). The sometimes occurring side-effects observed in commercial drugs (as nausea, etc.) stem from such problems of drug selectivity. More severe, but fortunately less common, are toxic side-effects. Selectivity, however, not only poses a problem for existing drugs, but also hampers drug development severely: A large majority of small drugs in research do not make it to the market. Thus they will never become an actual market drug, simply because it would be too dangerous to use them. In some cases, as for example in chemotherapy for cancer, conditions are so severe, that one takes in account severe side effects to achieve improvement of the condition. Herein, reducing side-effects would reduce suffering of patients tremendously.

Why are Drugs not Selective?

Organisms are very complex. They rely on complicated, intertwined networks of metabolic and signaling pathways. Targeting selectively a very small part of such a complex system is very challenging. Many drugs interact with targets embedded in metabolic or signaling pathways. It is thus very difficult to develop and design drugs that do exactly what/where they need to, but nothing/nowhere else.

Resistance and evolutionary pressure

Another problem associated with drugs is the possible formation of resistance . This is especially the case for antibiotics, but also true for other bioactive compounds (fungicides, antivirals, etc.). Often, the accumulation of active drug molecules in the environment leads to evolutionary pressure for the targeted organisms to form resistances. Temporal deactivation with light might help to prevent such resistance build-up.