Why do drugs that do the same thing have different side effects in the same person?
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I asked my pharmacist this after I had some weirdly bad drug reactions. I’ll try and relay it accurately. I don’t think this applies to all medicines, but at least sometimes it’s something like this:
Your body takes ingested medicine through your digestive system, and it gets filtered through your liver.
Your liver has different types of tools it uses to break down things for your body to get rid of easier, and the amount of each tool is different in each person
Let’s say that you take medicine, it passes through your liver, and it needs both Tool A and Tool B to be processed properly. If you have a lot of Tool A, you can do the first round of processing really fast, and can break down part of the medicine right away. If you have too much, you can do this too quick, and Tool B can’t keep up.
If you don’t have enough of Tool A, the medicine might take a long time to wear down, or it’ll just pass through unchanged. Tool B might not be able to break down unchanged medicine, so it can’t help. You might have the useful bits of medicine get sent away too fast to use
Even if you have the right amount of Tool A, if you don’t have enough of Tool B, things can still go wrong. Tool A could send Tool B too much and overwhelm it, and it could take a long time for the medicine to get broken down and processed all the way. Partly broken medicine could stay working much longer than it’s meant to, and act stronger than intended
If one of the partly processed things causes a side effect, then that one can stay as long as it takes to get rid of the medicine, even if the useful bits have already been used up.
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