Why do medications cause side effects?

It’s true that drugs—chemicals that interact with our body—sometimes come with unpleasant side effects, which health care professionals try to minimize as much as possible. For example, almost all antihistamines (used to treat allergies) cause drowsiness.

These side effects exist because in the current state of pharmacological science, it is still not possible to create molecules that can act exclusively and specifically on viruses, bacteria, diseased cells, and basically all these tiny things that cause us pain and that we take drugs for. And this will probably be the case for a long time since the human body is an extremely complex machine.

Regarding the efficacy of a drug, which varies from person to person, we need to understand that genetic factors, including those affecting metabolism, can have a major impact on the effects of a drug. This is why, for the same dose, in two people of identical weight, a drug can be either effective or totally ineffective, and come either with no side effects or with serious undesirable ones.