It depends what you mean by chemical. Most manufactured drugs are actually derived from natural substances! The trouble with many ‘natural’ medicines is that there is very little scientific evidence that they work. When a new drug is developed, it must go through a lot of serious testing before it is allowed to be given to patients – it’s extremely important that we know if there are any side effects from using it, and whether or not it actually does what we’re expecting it to. With a lot of natural medicines however, there have been fewer studies looking at how effective they are. They might work for some people, but they might make others actually worse. Some types of medicine haven’t been proven to work at all – things like homeopathic medicines are very dubious.