You assume, I take it, that God is all-powerful and perfectly benevolent, so that (at least on the face of it) there should be no evil in the world. You also, I assume, consider a 'high' - resulting from the recreational use of psychoactive substances - to be an evil, or at least something harmful we would be better off without.
There are (at least) two ways of looking at this.
1 Is a 'high' an evil ? Is it necessarily harmful ? It can have totally undesirable consequences, but then so can virtually any activity or experience.
On the whole, though, I agree that there are definite, regular and extensive causal links between the recreational use of such substances and serious harm to individuals and society.
2 Grant that there is a God who created the universe. It does not follow that the occurrence of 'highs' is any part of God's purpose. It may be a part of our purpose as human beings, or of those human beings who want highs, that 'highs' happen. God could certainly, as omnipotent, have created a world in which no 'highs' do or can occur. The standard response to your question is that God gave us free will, by which (as it happens) we can induce 'highs', and that since God is perfectly benevolent it must in God's perfect judgement be better for there to be a world in which people can use their free will to induce 'highs', harmful as they are to individuals and society, than a world in which human beings do not have free will which they can harmfully use - in this case to induce 'highs'.
3 How this can be so, only God knows ! I am baffled how a God-of-all-the-perfections can allow animal pain. What purpose does this serve ? All these matters are a part of 'the problem of evil', a problem vast and deep and beyond the scope of any adequate answer here.
I appreciate your seriousness but I doubt if philosophical reason rather than religious faith will assuage it : and religious faith, whatever its status, is beyond the scope of PSE.