A new study has found that laughing gas, a common anaesthetic used by dentists, increases the vividness of imagination and also increases suggestibility, making people slightly more likely to experience hypnosis-like suggestions.

The study, just published in the medical journal Psychopharmacology, stems from the informal observations of dentists that patients under laughing gas (nitrous oxide) sedation are particularly suggestible and the researchers aimed to test this out in more detail.

The researchers randomised patients at a dental surgery to either receive a nitrous oxide and oxygen mix, or just oxygen, with the patients not knowing which they were receiving. Two weeks later they were invited back and given which ever type of gas mix they hadn’t already had.

While inhaling each gas mix, the participants were asked to complete a measure of imaginative ability, rating the clarity and vividness of their visual imagery, as well as being given various suggestions – without the hypnotic induction – from the Stanford Hypnotic Susceptibility Scale.

This includes suggestions that your hands might move of their own accord, to suggested temporary paralysis, to a suggestion to experience hallucinated sounds – to name but a few.

The researchers found that nitrous oxide boosted imaginative ability considerably, and increased suggestibility modestly but reliably.

The paper discusses the small but interesting literature on which drugs affect suggestibility, and reviews some of the past studies which have tested some quite surprising substances in this way:

Little research has investigated the effects of other drugs upon suggestibility in a controlled manner. Sjoberg and Hollister (1965) administered lysergic acid diethylamide (LSD), mescaline and psilocybin separately and in combination to participants and measured imaginative suggestibility before and after drug administration. Gibson et al (1977) measured the effect of benzodiazepine administration upon hypnotic suggestibility, and Kelly et al (1978) tested the effect of cannabis intoxication upon the imaginative suggestibility of participants initially scoring low to medium on a standardised scale. Details of these studies and the resulting changes in suggestibility are given in Table 2 [see further down this page for a web version]. The greatest changes in suggestibility, in order of decreasing size, are evident after administration of nitrous oxide, cannabis, LSD, mescaline, combination of [LSD+mescaline+psilocybin] and diazepam.

So it seems that nitrous oxide may have a particular suggestibility boosting effect.

By the way, the study was led by psychologist Matt Whalley, who also runs the excellent Hypnosis and Suggestion website, undoubtedly the best internet resource for scientific information on hypnosis.

Link to study.

Link to PubMed entry for same.

Link to excellent Hypnosis and Suggestion website.