The only reason why we experience what we do are the effects of various neurons and brain areas and thus associating "happy" or "trippy" experiences. The fact that I can experience God without taking drugs or alcohol let's me know its not natural and even it was, why would God communicate with me while I just ingested something?
If you mean experiencing God without drugs is not natural -- or supernatural -- I disagree with you. Breathing meditation, centering prayer, chanting, prayers like the Rosary -- all of these things alter a person's consciousness, and scientific studies have shown that meditation even alters brain waves. The temporal lobe is also involved in mystical experience, and there are overlaps between drug-induced and spontaneously occurring mystical experiences. All of it is natural.
I do not recommend using drugs for a mystical experience unless under tightly controlled conditions. But however a mystical experience occurs, drug-induced, prayer-induced, spontaneously, or whatever, it involves the brain and our biology, which is increasingly being evidenced by the rather new field of neurotheology, the scientific study of spiritual or mystic states and/or experiences.
So, if you argue that a drug-induced mystical experience is not genuine solely because it alters brain function, the same is true of serious prayer, meditation, chanting, and so forth. The temporal lobe tends to be increasingly activated or unstable in spiritual experiences, as evidenced by the correlation of high levels of spirituality and spiritual experience with temporal lobe epilepsy.
This is how I personally distinguish a genuine mystical experience -- whether drug-induced or not -- from a more superficial experience masquerading as spiritual: genuine mystic experiences tend to create lasting changes. If a person says they experience God, but there are no lasting effects, I would think this experience in some way fundamentally differs from a similar experience that
does produce transformation and healing.
I think mystical experiences unlikely -- but not impossible -- from a recreational drug trip, but under controlled conditions, the odds go up that a mystical experience will occur. After all, shamanism is very ancient and often associated with drugs in controlled settings, rather like mental health professionals were able to use drugs to help clients in this way back in the 70s before so many drugs were made completely illegal. Again, I think the test of the genuine experience is whether it produces lasting change. Such an experience must be deeper and more transformative than a similar one that has no lasting impact.
As for why God communicates with someone ingesting a drug, if that does happen, and not everyone calls it "God," we don't really know, but the brain and biology are major factors.