Oneirogen

An oneirogen, from the Greek ὄνειρος óneiros 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.

Hallucinogenic oneirogens

Iboga alkaloids such as ibogaine and noribogaine and Silene undulata )
β-Carbolines and harmala alkaloids such as harmine, harmaline, tetrahydroharmine, 6-methoxyharmalan, and 6-MeO-THH and Banisteriopsis caapi )

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 β-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_2A receptor, neither iboga alkaloids nor β-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 κ-opioid receptor agonist. However, harmala alkaloids like harmaline do not interact with the κ-opioid receptor. Similarly, the NMDA receptor and the sigma σ₁ receptor do not appear to be involved in the subjective effects of ibogaine based on animal studies.

Dreaming-promoting oneirogens

Claimed

Calea zacatechichi has been traditionally used in Central America as a believed way to potentiate lucid dreams and perform dream divination. It can promote dreams vivid to the senses, sight, scent, hearing, touch, and taste. May be taken as a tea or smoked.Entada rheedei

Mugwort, see Artemisia douglasianaSilene undulata is used by the Xhosa people of South Africa to induce lucid dreams. It has been found to contain β-carbolines and ibogaine.

Possible

Diphenhydramine can invoke an intense hypnagogic REM-like microsleep often indifferentiable from reality. It accomplishes this by blocking various acetylcholine receptors in the brain.
Galantamine was shown to increase lucid dreaming by 27% at 4 mg and 42% at 8 mg in a 2018 double-blind study lasting three nights.
Melatonin receptor agonists like melatonin and ramelteon may cause vivid dreams as a side effect

Disputed

Valerian (herb) – A study conducted in the UK in 2001 showed that valerian root significantly improved stress induced insomnia, but as a side effect greatly increased the vividness of dreams. This study concluded that valerian root affects REM due to natural chemicals and essential oils that stimulate serotonin and opioid receptors. Another study found no encephalographic changes in subjects under its influence.

Non-pharmacological

Mindfulness practices could be useful in achieving lucid dream.
Sleep deprivation can make dreams more intense, which is caused by REM rebound effect