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AlmondMagnum
Like I said it's not a mental altering substance, where did you get tis strange notion from?
The brain, a.k.a. mind, controls literally every substance in our body. Under your argument every single medication is a mind altering medication because even diseases and vitamin levels leave an immediate impact in one's behavior.
No, Lust is not controlled by mind, it's an arbitrary function(not a mental one) which comes as a result from increasing the levels of certain hormones in the human body, if can impact on ones behavior but it doesn't really affect a person's set of emotions and personality directly. Which is why normal, sane people can actually control themselves and even stop that lust if they feel it's going to bring negative influences upon themselves. Those that can't for some reason, are the ones who become rapists and other kinds of criminals(you can lust for things other than sex).
The brain controls everything, be it through conscious effort or unconsciously. Therefore everything that happens in your body can be considered a "mental function" however that's not how it works. The brain only gives orders, lust is the natural result of your body sending signals to your brain an asking for an erection for an impending intercourse. The brain merely accepts the request and let the hormones work. The resulting effects of that lust are not really regulated by the brain itself, as different people have different results in anything related to such stimulus. Frankly I don't understand why scientists who study emotions insist on correlating love with sexual attraction in their studies, when both are clearly very different from one another(you don't need to lust or want to bang someone to love them, a.k.a. having your brain consider that person as a priority when activating one's self defense mechanisms).
As for your last point, no it's not easy to overdose. Remember the girl used the entire bottle in one go. It's literally the same as expending an entire tube of toothpaste in a single day. Even though it shouldn't cause any harm to your teeth normaly, and as such it wouldn't be regulated. It will still cause damage to your teeth if you used the entire thing in one go by washing your teeth for hours. Moreover there's no such a thing as "needing regulation" in this case because:
1. this is literally the only bottle of such medicine in the world; And...
2. the MC had already determined this action to be necessary, and he would be the doctor in question to tell which kind of medicament a person should use. Since no one else would have this kind of knowledge in this specific world.