The Lumenate app. Or if you don't count oxygen as a drug: Breathwork (Holotropic Breathwork, Quantum Light Breathing, Shamanic Breathing, Rebirthing, etc.). N

The Lumenate app. Or if you don't count oxygen as a drug: Breathwork (Holotropic Breathwork, Quantum Light Breathing, Shamanic Breathing, Rebirthing, etc.). Never tried but I heard that multi-day retreats in complete darkness can also induce some kind of (visual) trips.