I understand bacteria can mutate and develop resistance against antibiotics, but I do not understand how finishing an antibiotics treatment prevents this. In my simple thought process, when an individual bacterium has a mutation with antibiotics resistance, the antibiotics do not work on it. So whether I take 1 antibiotics pill or finish the whole treatment would not kill this bacterium, leaving it able to multiply later.

I am guessing the actual situation is either one of these things:

  • The immune system itself, relieved of pressure by most bacteria being dead, kills the bacteria that developed resistance. Important note here would be that if the immune system is completely shut down, perhaps finishing an antibiotics treatment would actually INCREASE resistance as only the bacteria with resistance would survive. So I suppose this theory is wrong.
  • Even individual bacteria only developed resistance which is not the same as immunity and bombarding it with antibiotics for multiple days still (usually) means that the bacterium dies.

Does that make sense or is there a thing I'm overlooking here?

  • You are prescribed enough to ensure that all of them are gotten and if you don’t take the full dose you can’t ensure how many survive and mutate
    – Joe W
    Commented Jun 17, 2018 at 18:04
  • @JoeW I'm sorry but comments are not for answering the question, and that is not a source-backed answer either, nor does it really explain anything. Commented Jun 18, 2018 at 8:01

1 Answer 1


Mayo Clinic on the example of tuberculosis:

Stopping treatment too soon or skipping doses can allow the bacteria that are still alive to become resistant to those drugs, leading to tuberculosis that is much more dangerous and difficult to treat.

So, the logic behind completing the course is to kill as much bacteria as possible to prevent the surviving ones to mutate and become resistant.

UPDATE: This question seems to be quite complicated, actually.

According to The BMJ (2017):

However, the idea that stopping antibiotic treatment early encourages antibiotic resistance is not supported by evidence, while taking antibiotics for longer than necessary increases the risk of resistance.

The official policies of prescribing antibiotics have not changed because of such discussions, but the BMJ authors recommend that the information material for the public should contain "take antibiotics exactly as prescribed" and not "finishing the course." So, it's a doctor and not a patient who should decide the treatment period.

  • “If you are continuing with antibiotics for too long, the non-resistant pathogenic bacteria and the harmless bacteria (a part of normal body flora) will die thus leaving more room for the antibiotic-resistant bacteria to grow.” But I’m not talking about taking the antibiotics for too long but for the regular prescribed amount of time. This quote shows the reverse of the thing we’re always taught, that not taking all pills for the prescribed period causes antibiotics resistance, while this quote says that is actually caused by taking it too long. Commented Jun 18, 2018 at 8:41
  • For the record, I think it makes a lot of sense what you're saying, but as far as I know doctors always hammer on the fact that you finish the treatment, not that you don't take more than advised. And I thought they did this because of resistance. Commented Jun 18, 2018 at 8:45
  • 1
    Yes. Some people stop taking antibiotics as soon as they start to feel better.
    – Jan
    Commented Jun 18, 2018 at 11:06
  • 1
    So, the instruction is just some kind of insurance that the antibiotics kills all the bacteria? What if the side effects cause harm?
    – Nobody
    Commented Jun 18, 2018 at 11:10
  • 1
    I removed the abstract link from PubMed Health and kept only the original BMJ article. You can say that the BMJ article is only an opinion piece,but this piece says that the current policy to finish the antibiotic course is also just an opinion not supported by evidence. Such discussions, if supported by evidence from future studies may lead to change in the antibiotic prescription policy.
    – Jan
    Commented Jun 19, 2018 at 9:09

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