Medications vary dramatically in how they effect people. For instance, while Topamax has earned the nickname "dopamax" by some of those who take it, in the last two years I've taken it, my verbal abilities have actually skyrocketed, in that my word recall has actually improved and the generation of spontaneous speech (as well as written language) has increased at a quick rate. I am probably an outlier (given that for most people, it either has no/minimal side effect(s) or a negative effect, from what I can gather, though the perceived increase in verbal ability may be a coincidental developmental improvement more related to brain development and environmental circumstances as opposed to a causal link with the drug), although it did result in fairly significant dry mouth, remedied easily enough by monitoring water intake and using lip balm, but the fact remains that what is someone else's horror drug might be your wonder drug (I also tend to require low doses of drugs to obtain therapeutic effects).
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"There are things you need not know of, though you live and die in vain,
There are souls more sick of pleasure than you are sick of pain"
--G. K. Chesterton, The Aristocrat