The phenomenon of antibiotic resistance is well known: an antibiotic is effective when first introduced to the market, but over the years, its effectiveness decreases as resistant strains of bacteria emerge.

Are there other kinds of drugs which experience similar phenomena, where over time they become less effective at treating the disease they were originally developed for?

(I'm not asking about the "decline effect", noted amongst antidepressants, where repeated studies seem to show a decrease in effectiveness, which seems to be a symptom of poor quality or biased studies overstating the drug's initial effectiveness.)

(I'm also not asking about drugs whose effectiveness for a given patient decreases over time.)

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    Have you thought about why antibiotic resistance occurs? Can you think of other drugs where that mechanism would make sense? Can you think of other drugs for which that mechanism wouldn't make sense?
    – Bryan Krause
    Jun 17, 2020 at 14:36

1 Answer 1


This type of phenomenon will almost always be seen with drugs that target foreign pathogens capable of change, i.e., bacteria, viruses, fungi, parasites, etc. In addition to antibiotics, which target bacteria, antiviral and antifungal medications can also decrease in effectiveness overtime as the pathogens develop resistance mechanisms. For instance, HIV can mutate over time as is written here:

This is because HIV replicates at an extremely rapid rate and does not contain the proteins needed to correct the mistakes it makes during copying.

This is the reason people with HIV take multiple antiviral medications at the same time ("combination therapy) -- this mitigates any potential resistance from occurring because even if resistance develops to one drug, that mutated strain will be killed by the other meds which work by a different mechanism. It is highly unlikely HIV could develop resistance to three different kinds of antivirals in one strain.

I cannot think of any other medications that would decrease in effectiveness over time, even when thinking about factors such as change of seasons or climate change.

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