What stops people from poisoning your food? What stops your nervous system from producing drugs?
Make your own food so you know what's in it, you can even raise your own livestock, grow your own crops, and filter your own water.
The chemicals produced by your nervous system are not fitting the definition of drugs, but you can still regulate them of they worry you, in fact, that's a large part of where abstinence activities like swearing off pornography and masturbation come in, as activities like these could cause your brain to produce chemicals that have a negative effect on you, the good part is that even of you fail, so long as you resisted even of only for a little bit, already has a good effect and makes the next attempt easier, it's typically only through setting milestones and multiple failures that we make progress and win success.
Also, a lot of the chemicals you produce, such as when you are working out, can also be moderated if they concern you, as well, but yeah, its good that you brought this stuff to our attention as well, its easy to overlook.
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