That's not really a silly question :) Drugs act on proteins which are little machines in the body, the instructions of which are encoded in our genome. The sli

That's not really a silly question :) Drugs act on proteins which are little machines in the body, the instructions of which are encoded in our genome. The slight variations in our genetic code leads to some proteins having slight variations in their structure (and their function). Most of the time this is harmful, but sometimes it causes them to react differently when they interact with a drug or with each other. The manifestation of this can sometimes be harmful. Understanding "pharmacogenomic" effects will help us mitigate these side-effects going forward.