The administration of a chemical can cause zero effect to many effects in the body. For simple understanding, side effects of medicines can be defined as effects that aren't the intended effects of the administration of the medicine. Side effects can be known effects or unknown effects too.

A false sense of security is no security at all. Therefore, it must be noted that natural medicines (medicines that are sourced naturally from naturally occurring materials, or whatever they mean) can have side effects too. As an example, consider the many damages caused to liver by various herbal supplements and liver detoxes advertised to be natural. There are very many scientific studies on this issue.

Often, synthetic medicines being "chemicals" is blamed for it's side effects; and natural medicines not using "chemicals" is credited for it's "no side effects". We get the point that they are trying to make, except that it is inaccurately articulated. At the fundamental level, everything is a chemical and almost every medicine is manufactured — either in a factory or in a kitchen. Therefore, to categorically say that natural medicines do not contain chemicals is wrong.

Perhaps, they mean that no chemicals that are manufactured as chemicals and look as chemicals — like a powder or a bottle of liquid — are used in the manufacturing of natural medicines, and therefore, no side effects. This thought rises from the misunderstanding that all chemicals and compounds that naturally exist in the environment go well with the biological functioning of our body, and side effects are caused only by those compounds that look and feel like chemicals to our mind. If you consume a poisonous fruit, there will be fatal side effects to it.

Therefore, it is wrong to categorically say that naturally existing chemicals don't have side effects. What creates an effect is the "acceptance" of the administered chemical by the body (and most chemicals will have an effect in the body). What creates a side effect is whether the effect was intended by the medicine — if it wasn't, it becomes a side effect. Such chemicals that induce unintended effects, or side effects, are found abundantly in nature and can also be manufactured.

The idea of natural medicines causing side effects have been embodied well in the traditional Malayalam saying, which is often spoken in traditional medicinal discussions too, "Adhikamaayaal amrtham visham", meaning that a divine necter (contextually medicines) can be a poision if consumed more than required. So, for the sake of your own health, be sure not to wallow in the idea of natural medicines not causing side effects.

The side effects of natural medicines, however, may not be as abundant and evident as the side effects of synthetic medicines. And in due time, this difference may not be significant, since the side effects of synthetic medicines are declining drastically from improved technology.