And even if they didn’t, the body is a tightly interconnected system. Taking an antidepressant to “selectively affect serotonin” in the brain? Whoops, turns out your gut has at least as many serotonin receptors as the brain. Taking a statin to reduce cholesterol (which it does very well but with an NNT > 200 for heart attacks and NNT > 300 for stroke)? Whoops, it causes transient global amnesia and personality changes and diabetes in a lot of people. And 40% of the US Adult population we’re on statins in the mid 2000s.