Altered states of consciousness induced by hallucinogens (H-ASC) is still a vaguely understood phenomenon. Taken the diverse psychological effects they exert, the main mechanism of action of hallucinogens; LSD, ibogaine, THC, PCP, MDMA, methamphetamine, mescaline, psilocybin and DMT, of which psychological effects are discussed in the article, are not properly understood and explained by the modern methods of neuroscience due to the lack of vigorous research. The involvement of some receptors, such as, 5-HT2 (and probably other 5-HT receptors), glutamate and dopamine receptors, adrenergic and cannabinoid receptors, is one of the mechanisms, however it is not easy to explain such incongruent psychological effects by only receptor and neurotransmitter systems alone, since H-ASCs have, sometimes, their own unity and gestalt, unfolding the subconscious, in the “voyages” they induce, although the perception may, or may not, be distorted depending on the person, and “set and setting”. They induce visual, tactile and auditory hallucinations; synesthesia; perception of fractals, geometrical and kaleidoscopic images with vivid colors; perception of two dimensional pictures as three dimensional, animated and moving; distortions and alterations in the body perception; alterations in the perceptions of temporal-spatial continuum and time; changes in the perception of the ego and the self; feelings of unification with nature and universe, peak experiences –mimicking satori or nirvana-, ecstasy, rapture, extreme euphoria, excitement and happiness, oceanic bliss, self-fulfillment, referred as “good trip”, as well as, dysphoria, anxiety, mania, delirium, psychosis, acute schizophrenia, collapse of the self, known as “bad trip”; depending upon the mood, affection and psychology of the person, and “set and setting”. Mysticomimetic effects of H-ASCs, imitate the consciousness states of ancient mystics, probably, by means of activating prefrontal cortex, limbic system and the right temporal lobe. A hypothetical “holographic brain theory” may give some extra insights about the explanation of some of the effects of H-ASCs. It should be taken into account that H-ASCs, can be accepted as a good tool to investigate the nature of consciousness, brain and the human psyche, as well as some of the H-ASCs are good models of psychosis, too. More detailed scientific research should be performed to understand the basic and real mechanisms of H-ASCs, to comprehend and unravel the mystery of human mind and consciousness, since scientific medical research on hallucinogens has been legalized since 1992.