Why aren’t here any drugs that fix the targeted issue but have no risk of creating new issues elsewhere?
In: Biology
There are multiple reasons. First, as others have said, evolution likes redundancy. If you can make one thing do five different things, that takes a lot less energy than to make five different things do five things, for example serotonin regulates mood but it is also the precursor molecule for melatonin that regulates sleep, so a drug that helps your body to absorb and process serotoninmore effectively can inadvertently cause drowsiness because it also increases melatonin by proxy (which is why some people with depression also have insomnia and why some forms of depressioncan be treated with melatonin supplements.)
Second, sometimes the side effects are as a result of the drug doing what it is supposed to too effectively, for example, Advair is what is known as an “antiesonophil” which means that it surpresses the part of the immune system that targets parasites and fungi (because your body is mistakenly identifying your lungs as a parasite or fungus causing asthma attacks) but because of that, if you don’t rinse your mouth and throat it can cause the body to not fight off a fungal infection causing thrush. More relevant, immune-suppressants used to treat auto-immune disorders (such as certain forms of arthritis) can reduce the body’s ability to fight off certain forms of cancer because part of the auto-immune system is identifying carcinogenic cells and killing them before they can form tumors.
Third is the biosimilarity of some pathogens to the human body. Antifungal and antiparasitic treatments tend to have more side effects than most other antibiotics because fungi and parasites have more in common with people than bacteria, so drugs that inhibit or harm them may also do the same for some of our cells.
Lastly, there is the issue of opprotunistic infections of biota that serve a function. Bacteria in our gut help us with digestion, and there is bacteria on and in the vagina that produce chemicals that inhibit fungal growth. If those bacteria are transferred elsewhere into the body and develop an infection, then the antibiotics used to treat the infection have a high chance of killing off the native biota, causing diarrhea and a possible fungal infection.
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