SSRIs work by increasing the amount of serotonin in your brain. But they can also have side effects like constipation (the internet says SSRIs block acetylcholine?), and you can’t take NSAIDs too because of a risk of stomach bleeding. How do SSRIs do those things if they are focused on serotonin? Does acetylcholine use the same receptors as serotonin? I’m also interested in how they cause other side effects.
In: Biology
I think a common misconception of drugs in general is that they only end up in the tissue they are meant to be in, for example antidepressants in the brain. In reality, when you take a pill that compound ends up pretty much everywhere throughout the entire body. Most drug side effects arise from activity in tissues other than the target one (liver, heart, intestines, etc.)
There is some research ongoing into targeted delivery systems, but with a plain old small molecule like an SSRI this is an insurmountable problem.
Going just a bit deeper, pharmacological effects result from the binding of a drug molecule to its intended target in the body. And the drug doesn’t know where it is going, it is just bouncing around the body randomly until it finds something it has high affinity to, then it sticks around for a while. Modern medicinal chemistry has gotten fairly good at manipulating chemical structure to build in selectivity (given a lot of time and resources) but designing something that only binds to one of the countless proteins, enzymes, receptors, etc. in the human body is a tall order.
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