I was looking for a forum that had scientific merit on the phenomenon of natural halluciations, which I endured as a child, and I came across this discussion on hallucinations. I am appalled by the lack of knowledge and misinformation represented here.
To the poster that said a friend had took LSD and subsequently gauged their own eyes out with a spoon because of flashbacks!?! Grow up. Flashbacks are at most a feeling of disassociation, slight audio echoes and visual hallucinations... very slight. The flashback effect has been extremely sensationalised by the governments medical branch. The government has a history of lying to its citizens, take the film "Reefer Madness" as a case in point. People jumping out of windows believing they could fly is another urban myth. LSD is NOT an hallucinogen, it is a pseudo-hallucinogen. It also doesn't seem to bring about the most striking effects on first use (tracers etc.).
Whoever recommended starving your brain of oxygen, or inducing hyperventilation, should be banned from posting. This kind of experience should not be attempted in a non-medical environment, and it has a very low chance of success. I'd feel safer telling someone to amputate their arm at home than this. If you must interfere with breathing, then do it using meditation breathing techniques, but don't expect open-eyed hallucinations.
As for someone disagreeing with science on how safe hallucinogens like LSD and mushrooms are, just because this isn't a hippy/psychedelic forum, is just unbelievable. Science and independant research has shown that the classification of LSD, DMT, psilocibin etc. into the most controlled category has absolutely nothing to do with how harmful these substances are. The substances create fear in ignorant people, and this has been leveraged by politics on multiple occasions without regard for the reality of things. Just because you don't like the results of the science, doesn't mean it should be ignored. Really, don't let people make a mockery of science in a scientific forum.
There are many genuine methods of inducing hallucinations, and i'll try and give a quick guide to a few.
Morning Glory, Baby Hawaiin Woodrose:
These are a simple and relatively safe way to experience a pseudo-lsd trip. They contain LSA the precursor to LSD, however if you bought Morning Glory from a supermarket it will have been treated with chemicals that are extremely unpleasant. The husk of both types of seeds contain chemicals which will also make you vomit, so if you don't want to taint your experience with feeling ill, don't do it. Incidentally the strongest Morning Glory LSA content comes in three varieties - Heavenly Blue, Flying Saucers and Pearly Gates.
Datura, Belladonna, Amanita Muscaria:
Keep away from all of these plants, they are extremely toxic and will cause delerium not just hallucincations.
Pscilocibin mushrooms:
The type depends on your location, but these are simply the best method of inducing a first time hallucinogenic experience. Do not underestimate it though, because you can go to heaven or hell, and unless your experienced the only way back is when you come down. They are also short acting (5-6 hours), and natural unlike LSD.
DMT containing plants, the Bufo toad:
This is the most profound experience of them all, but its cultivation and preparation are extremely difficult and I wouldn't recommend it. There are plenty short break vision quest style holidays available that will give you the experience safely. Check out 'Eagles Wing' for an example. However this experience is not for the faint of heart, prior hallucinogen experience is definately a prerequisite before attempting this. The Bufo toad secretes DMT and as has been stated can be licked, probably smoked for the effect. Given its location and chance of capture, don't bother. Additionally there are plenty of seeds containing hallucinogenic material used as snuff, called yopo. This isn't very pleasant in any sense of the word, and not something I'd recommend.
Mescaline producing Cacti:
I have no experience yet with these, but mescaline was used in visionary practices of native indians. Peyotl was revered as a deity by the maya and central American civilisations. It is considered extremely safe, although that is clinical grade mescaline, the cacti contains hundreds of additional alkaloids, and its common to vomit as the effects come on. Huxleys 'The Doors of Perception' is all about his experience with mescaline.
Lucid Dreaming:
Easiest and least harmful of them all, there are plenty of factual websites on this phenomenon, and if you are lucky enough to have done this naturally in the past, then it should be easy to train yourself. Strangely nicotine patches seem to induce lucid dreaming, although most people consider them 'nightmares'. Being able to bend the world around you til your hearts content, have any experience you want, and do this in the dead time you call sleep, are all excellent reasons to take up this 'hobby'. Thoroughly recommended.
Trance Dancing:
Rythmic percussion and chanting for several hours can induce a trance, possibly hallucinations, but only if your an experienced practitioner. I've not experienced this, I'm too reserved to practice this in modern society.
Sensory Deprivation, Sensory Overload:
I've no experience on this, but to find out more check out native American Vision Quests, as these often include days in the wilderness.
My advice, either lucid dream or psilocybin mushrooms. Any other method will probably be stupid.