An oneirogen, from the Greek á½ÂýõùÃÂÿàóneiros meaning "dream" and gen "to create", is a drug that induces a dream-like state of consciousness, also known as oneirophrenia. The term oneirogen, oneirophrenic, or oneiric, was introduced to refer specifically to ibogaine- and harmaline-type hallucinogens by William Turner and Claudio Naranjo in the 1960s and 1970s. Subsequently, the term has also sometimes been used to refer to non-hallucinogenic drugs that facilitate dreaming.
These compounds are notable in being structurally similar cyclized tryptamines and in being structurally related to psychedelic tryptamines. For example, ibogaine is a cyclized derivative of 5-MeO-DMT, while harmaline is a cyclized derivative of 6-MeO-DMT.
The hallucinogenic effects of these drugs are qualitatively unique and have been described as a "dream-like" altered state of consciousness. Iboga alkaloids and ò-carbolines or harmala alkaloids have similar qualitative effects, but show distinct subjective effects from those of serotonergic psychedelics.
Ibogaine and noribogaine are so-called "dirty drugs" that are known to interact with numerous targets. However, the precise mechanism of action of oneirogens like ibogaine, or whether their hallucinogenic effects are due to multiple concomitant activities, are unknown. While they can still bind to the serotonin 5-HT<sub>2A</sub> receptor, neither iboga alkaloids nor ò-carbolines actually activate the receptor, unlike serotonergic psychedelics. In addition, ibogaine does not produce the head-twitch response, a behavioral proxy of serotonergic psychedelic effects, in rodents. Noribogaine, the major active metabolite and form of ibogaine, is known to be a potent atypical ú-opioid receptor agonist. However, harmala alkaloids like harmaline do not interact with the ú-opioid receptor. Similarly, the NMDA receptor and the sigma ÃÂ<sub>1</sub> receptor do not appear to be involved in the subjective effects of ibogaine based on animal studies.