LSD enhances suggestibility in healthy volunteers, R. L. Carhart-Harris et al., 2014

LSD enhances suggestibility in healthy volunteers

R. L. Carhart-Harris, M. Kaelen, M. G. Whalley, M. Bolstridge, A. Feilding, D. J. Nutt

Psychopharmacology, 2014

DOI 10.1007/s00213-014-3714-z



Rationale : Lysergic acid diethylamide (LSD) has a history of use as a psychotherapeutic aid in the treatment of mood disorders and addiction, and it was also explored as an enhancer of mind control.

Objectives : The present study sought to test the effect of LSD on suggestibility in a modern research study.

Methods : Ten healthy volunteers were administered with intravenous (i.v.) LSD (40–80 μg) in a within-subject placebocontrolled design. Suggestibility and cued mental imagery were assessed using the Creative Imagination Scale (CIS) and a mental imagery test (MIT). CIS and MIT items were split into two versions (A and B), balanced for ‘efficacy’ (i.e. A≈B) and counterbalanced across conditions (i.e. 50 % completed version ‘A’ under LSD). The MIT and CIS were issued 110 and 140 min, respectively, post-infusion, corresponding with the peak drug effects.

Results : Volunteers gave significantly higher ratings for the CIS (p=0.018), but not the MIT (p=0.11), after LSD than placebo. The magnitude of suggestibility enhancement under LSD was positively correlated with trait conscientiousness measured at baseline (p=0.0005).

Conclusions : These results imply that the influence of suggestion is enhanced by LSD. Enhanced suggestibility under LSD may have implications for its use as an adjunct to psychotherapy, where suggestibility plays a major role. That cued imagery was unaffected by LSD implies that suggestions must be of a sufficient duration and level of detail to be enhanced by the drug. The results also imply that individuals with high trait conscientiousness are especially sensitive to the suggestibility-enhancing effects of LSD.

Keywords : Serotonin . Hallucinogens . Psychedelics . LSD . Suggestibility . Hypnosis



Lysergic acid diethylamide (LSD) is an ergotamine derivative with a high affinity for and agonist properties at several different neurotransmitter receptors; however, signalling at the serotonin 2A receptor (5-HT2AR) is thought to be crucial for its psychedelic effects (Nichols 2004). The remarkable psychological properties of LSD were first discovered by Albert Hofmann in 1943 (Hofmann 1980), and thereafter, LSD was investigated as a psychotomimetic (Fabing 1955) and tool to assist psychotherapy (Savage 1957) before regulatory restrictions in the mid-1960s that effectively suspended all of the relevant scientific research (Nutt et al. 2013; Stevens 1987). In the early 1950s, cold war pressure motivated a search for new methods to enhance interrogation and behavioural control, and in this climate, a covert programme of research code named ‘MK-ULTRA’ was commissioned by the US government to explore the potential of LSD to facilitate mind/behavioural control (Marks 1979).

Suggestibility refers to an individual’s susceptibility or responsiveness to suggestion. Suggestions can be given for alterations in the contents of consciousness and can target perception, sensation, cognition, emotion or behaviour. Suggestibility can be measured behaviourally, i.e. by the performance of suggested behaviours, or subjectively via the reported vividness or realism of suggested subjective experiences. Classically, a strong response to a suggestion is accompanied by the feeling of ‘involuntariness’ (Weitzenhoffer 1980), and suggestions have been demonstrated which allow participants to overcome normally automatic responses, such as word comprehension in the Stroop effect (Raz et al. 2002).

Different forms of suggestibility have been proposed, e.g. primary, secondary and interrogative suggestibility (Eysenck and Furneaux 1945; Gudjonsson 2003). The present study focuses on primary suggestibility defined as the induction of thoughts and actions via suggestion (Eysenck and Furneaux 1945). Assessments of suggestibility are often delivered following a hypnotic induction and are said to assess ‘hypnotizability’, but the same items can be delivered in the absence of hypnosis in which case they assess ‘imaginative suggestibility’ (Braffman and Kirsch 1999; Hull 1933) which is the ability of an individual to engage in fantasies that have the potential to alter his/her behaviour and/or subjective experience. Hypnotic suggestibility is strongly predicted by imaginative suggestibility (Braffman and Kirsch 1999), and both can be considered forms of primary suggestibility.