It's easy to get hooked into the habit of just trying new things. They call certain drugs gateway drugs, but in reality sometimes its just you are chasing a feeling or a mood, and end up trying everything.
By all means try things, but not all in one go, and space it out. Perhaps just weekends. There are good and bad drugs out there - one mans euphoria is another mans poison - and it's easy to get hooked to matter how many times you tell yourself "i can stop if i want to".
It's things like habituation, and duration that get u in the end. Have sober days/weeks. Don't overdo it. And if u do end up with something that grabs u, watch out for the whole tolerance/addiction cycle. Space it out man. Don't go 24/7. Sounds to me like you / your friend is just constantly chasing that "high".
Play games, watch movies, read books, get out, do something else. Theres a lot more to life than drugs. Get a hobby (Everyone has an obsession, even if they haven't found it yet). Drugs will get u if u overdo it. But if u plan it right, and like I say try to space out the usage, you'll be ok.