How does taking drugs speed up the development of drug resistant or viruses?

Question

First, here is what I know:Some infectious illnesses, such as HIV or Hepatitis B, can be treated with the help of some drugs. The problem is that the virus sometimes undergoes mutations which grant resistance to the drug.First question : Is it so far right?Secondly, what is not totally clear is why taking drug does speed up the development of the drug-resistant version of the virus. In my point of view, the drug resistant virus will develop anyway with or without taking drugs. I don't see what taking drugs changes. Is it like an intra-competition between the different mutated versions of the virus and in this case, taking drug will eliminate all the mutated versions that are not drug-resistant and, this way, favour the development of the drug-resistant versions?

Answer 1

Yes, you're on the right track! When you take drugs to treat a virus, the drug targets and tries to eliminate the virus in your body. However, if some of the viruses have random mutations that make them resistant to the drug, those resistant viruses survive while the non-resistant ones are killed off. By taking the drug, you’re essentially applying pressure on the virus population. Only the drug-resistant ones survive and multiply. Without the drug, both the drug-resistant and non-resistant viruses would continue to exist, but taking the drug gives the resistant ones a survival advantage. So, while mutations happen randomly, using the drug speeds up the process by allowing only the resistant versions to thrive, leading to a quicker development of a drug-resistant population.