Research into the beneficial effects of psychedelic drugs, such as LSD and psilocybin, is making something of a comeback in recent years. A number of recent studies have re-examined the therapeutic potential of these drugs in treating psychological problems, including depression, anxiety, and addiction, subjects that were originally explored from the 1950’s to the early 1970’s until research on the topic was effectively halted. Some of this old research suggested that LSD could increase a person’s suggestibility, and a more recent study has revisited this topic. The authors of this study proposed that increased suggestibility might contribute to the psychotherapeutic effects of LSD that can occur in a proper treatment setting. Other research has indicated that psychedelic drugs such as LSD might perhaps increase receptivity to unconventional spiritual ideas in the longer term, so it would be interesting to consider whether increased suggestibility plays a role in this effect.

Vincent van Gogh/DeepDream Generator
Modern technology may be catching up with the inner world of psychedelic experience.
Source: Vincent van Gogh/DeepDream Generator

The power of suggestion is well known, although how it achieves its effects is not entirely understood. Suggestion can be employed to alter the contents of a person’s consciousness, and can produce changes in perception, thought, emotion and behavior. For example, a person might be given a suggestion that a part of their body will experience different sensations, such as warmth, cold, or numbness, and they may then begin to actually feel these sensations. Although suggestion is commonly associated with hypnosis, suggestions can be given effectively without a prior hypnotic induction. Individuals differ in how responsive they are to suggestion, a trait characteristic known as suggestibility. Psychedelic drugs have potent mind and perception altering properties, and a couple of studies in the 1960’s found that people became more suggestible than usual under the influence of LSD. A more recent study aimed to replicate this finding using more up-to-date measures of suggestibility (Carhart-Harris et al., 2015).

The study involved 10 participants, who had previous experience with psychedelic drugs and who were carefully screened to ensure they had no history of psychiatric illness. They were tested in two sessions, the first one involving an injection of a saline placebo, and the second an injection of LSD. In both sessions, they were given a suggestibility test and a mental imagery test. Prior to the sessions they completed personality tests assessing the Big Five traits, and the trait of absorption, which is the tendency to become fully immersed in experiences. Most participants experienced an increase in suggestibility under LSD compared to the placebo, which was statistically significant. There was a trend for participants to experience an increase in mental imagery but this was not statistically significant. Participants who were high in absorption tended to have higher suggestibility and more vivid mental imagery in both sessions. This is to be expected as absorption is known to be associated with being imaginative and having a stronger response to hypnosis and to psychedelic drugs. A more unexpected finding was that participants’ conscientiousness was strongly positively correlated with the degree to which they experienced an increase in suggestibility under LSD compared to placebo. That is, the effect of LSD on suggestibility was larger in more conscientious participants compared to less conscientious ones.

The authors of this study argued that increases in suggestibility under LSD might account for some of the psychotherapeutic effects observed by therapists who used LSD with their clients in the 1950’s and 60’s. The kinds of experiences clients had seemed to particularly reflect the expectations of their therapists. For example, clients of Freudian therapists tended to recall more childhood memories, while clients of Jungian therapists had experiences of a more spiritual nature. Hence, Carhart-Harris et al. argue that the way people interpret their psychedelic experiences might be influenced to some extent by suggestion. This could apply for example to whether a person interprets experiences during intensely altered states as being of a mystical or spiritual nature or whether they interpret them through a more secular framework.

Regarding the positive correlation between conscientiousness and increases in suggestibility, the authors speculated that conscientiousness is a form of self-control, and that LSD has the effect of loosening control over one’s inner experience. Therefore, people who are normally the most controlled have more room to change in this respect. This assumes that the ability to respond to suggestion requires a lack of self-control. However, it is possible to argue that suggestibility is a form of control over what are normally automatic processes. If this is the case, then perhaps people high in conscientiousness have a greater potential for control over such processes that is amplified by LSD. This is sheer speculation on my part though, and more in-depth research is needed to fathom this issue.

Due to the small sample size of the study by Carhart-Harris and colleagues, only very tentative conclusions may be drawn. Bearing this in mind, I nonetheless find the possibility that suggestion could play a role in the nature of the psychedelic experience to be intriguing. A number of old and new studies seem to indicate that psychedelic drug experiences may possibly have long-lasting influences on attitudes and beliefs in some people, particularly those who find their experiences profoundly meaningful. For example, consider the results of a study in the 1960's on a psychotherapy program incorporating the use of LSD (Klavetter & Mogar, 1967). There was a strong relationship between the perceived quality of the LSD experience and subsequent psychological growth. Those who had what the authors called peak experiences – that is, intensely positive experiences characterised by perceptions of beauty, understanding, and self-transcendence – experienced greater increases in subsequent psychological well-being compared to those who regarded their LSD experience as less satisfying, e.g. those who found the experience disappointing, frightening, or of no lasting significance. About 69% of participants were considered to be ‘peakers’ while the rest were considered ‘non-peakers.’ Psychological growth was assessed using a measure of self-actualization, a concept developed by Abraham Maslow to refer to the tendency to fully express one’s most healthy psychological potentials for creativity, fulfilment and love. About nine months after taking LSD, peakers scored significantly higher on a measure of self-actualization compared to non-peakers. The authors took this to support Maslow’s notion that peak experiences have a positive effect on psychological growth, although they were reasonably cautious about interpreting the findings. The self-actualization scale used included a broad range of items relating to psychological health, such as better appreciation of relationships, greater happiness, less anxiety, deeper understanding of beauty and art and so on. Additionally, the scale also included quite a few items relating to spiritual beliefs, including unconventional concepts, such as increased interest in and open-mindedness about things like mysticism, telepathy, reincarnation, and spiritualism, and peakers tended to score higher than non-peakers on these as well. I find it interesting that the authors of this paper considered openness to unusual spiritual ideas as being a feature of optimal mental health (something I consider rather questionable) and that participants in this study who had peak experiences also became more open to these kinds of ideas.

Studies on psychedelic drugs from previous decades, including the one I just described, were generally not all that rigorous by today’s standards, but it is still interesting to compare their findings to those of more recent work. For example, A more recent study on psilocybin (Griffiths et al., 2011; MacLean, Johnson, & Griffiths, 2011) found rather comparable results to those of the previous study I cited. I have written about this study previously, but briefly, about 60% of participants who took a high dose of psilocybin had a “complete mystical experience” which they regarded as having sustained personal significance and meaning more than a year later. These participants reported long-lasting positive effects of this experience including increases in the personality trait openness to experience, a more positive attitude towards life, and an increased belief that there is continuity of consciousness after death. One of the features of the trait openness to experience is an interest in novel and unusual ideas of all kinds, including those of a spiritual nature. This might be a factor in increased belief in life after death long after their psychedelic experience.

These studies seem to indicate that some people experience effects that last long after the initial psychedelic drug experience has concluded. As well as increased well-being, these effects include increased openness to unconventional ideas such as those of a spiritual and/or paranormal nature. According to a number of studies, there are many positive correlations between suggestibility, belief in the paranormal, mystical experience and the personality traits absorption and openness to experience (Atkinson, 1994; Braffman & Kirsch, 1999; Smith, Johnson, & Hathaway, 2009; Thalbourne, 2010). These characteristics may share a common foundation in the ease with which psychological material crosses the threshold between the unconscious and the conscious areas of the mind, a characteristic that the late Michael Thalbourne (2010) referred to as transliminality. In some people the barrier between the conscious and unconscious functions of the mind is more permeable than usual, and they are more prone to experience unusual mental states, such as mystical feelings of oneness with the universe, experiences which they consider to be of a psychic nature (e.g. apparent telepathy), and so on. As discussed in a previous article, people high in absorption tend to have the strongest response to psychedelic drugs, and absorption is a feature of transliminality. It might therefore be reasonable to think of the psychedelic drug state as involving a temporary and massive amplification of transliminality.

Wikipedia/DeepDream Generator
Some people claim to experience 'cosmic consciousness' or even communication with extra-terrestrial intelligences while on psychedelic drugs
Source: Wikipedia/DeepDream Generator

Carhart-Harris and colleagues (2012) argued that psychedelic drugs temporarily produce an “unconstrained style of cognition” due to alterations in normal brain activity (which I have discussed in this post). This might help explain why LSD can produce a temporary increase in suggestibility, as well as more profound alterations of consciousness such as mystical experiences. Perhaps this temporary state of unconstrained style of cognition leads to more lasting effects in some people. If it is true that psychedelic drug use can lead to long-term increases in openness to experience, as the MacLean et al. study suggests, then perhaps as a consequence people become more willing to entertain unusual ideas about the nature of reality, such as belief in paranormal and spiritual aspects of existence. If this is the case, might this represent a manifestation of a long-term increase in suggestibility? Future studies on LSD and similar drugs could look at whether users experience long-lasting changes in suggestibility and how these might be related to changes in their beliefs. They might also look at whether users experience increased receptivity mainly to “spiritual” ideas, or whether they become more open to unusual ideas in general. E.g. do they become more open to non-mainstream ideas about lifestyle, health, politics, and so on. If so, this might indicate that the mind-opening effects of psychedelic drugs might be very broad-based. It might also be interesting to see whether people who are higher in conscientiousness experience greater change in their beliefs and experiences compared to less conscientious people. Carhart-Harris and colleagues (2015) proposed that how people interpret psychedelic drug experiences might be influenced by the process of suggestion. Therefore, it might be worth considering whether the people who conduct these studies have a suggestive influence on the experiences of their research participants. For example, it is possible that researchers with particular spiritual interests might influence their participants to have experiences of a more spiritual nature, while researchers with a more secular orientation might have a subtly different influence. It would be important to know whether this is true, because subtle influences of this sort might interfere with the scientific objectivity of the research itself. This might be studied by comparing the outcomes of different research teams to see if there are any apparent biases in their findings.  

Vincent van Gogh/DeepDream Generator
An illustration of unconstrained cognition perhaps? Distorted visuals are a common experience on LSD. 
Source: Vincent van Gogh/DeepDream Generator

The research studies that I have reviewed here all have their limitations as this field is still in its infancy really, and the ideas that I have tentatively proposed here need to be regarded as speculative in nature. For example, at this time we cannot really be sure that psychedelic drug use actually does cause long-term changes in users' personality and beliefs. It is quite possible that people who are already open to change are drawn to experimenting with these drugs (and this may include those who are willing to participate in research on them) and that they simply act as a catalyst for changes that would have occurred anyway. (Personality psychologist Sanjay Srivastana discusses this possibility in an insightful critique of the psilocybin study by MacLean et al.) Hence, more research is needed in order to develop a deeper understanding of any potential long-term effects that these drugs might have. 

© Scott McGreal. Please do not reproduce without permission. Brief excerpts may be quoted as long as a link to the original article is provided. 

Image Credits 

I created the images by running Vincent van Gogh's The Starry Night and The Night Café, and a photo of the Andromeda galaxy through Deep Dream Generator a number of times. I hope I will be forgiven for taking what some might see as horrible liberties with great works of art!

Other posts about psychedelic drugs 

Psilocybin and personality

Psilocybin and brain function

Psilocybin for anxiety and depression in the terminally ill

DMT, aliens and reality – part 1

DMT, aliens and reality – part 2

DMT: Gateway to Reality, Fantasy or What?

The Spirituality of Psychedelic Drug Users

Peak Experiences in Psilocybin Users


Atkinson, R. P. (1994). Relationships of Hypnotic Susceptibility to Paranormal Beliefs and Claimed Experiences: Implications for Hypnotic Absorption. American Journal of Clinical Hypnosis, 37(1), 34-40. doi: 10.1080/00029157.1994.10403107

Braffman, W., & Kirsch, I. (1999). Imaginative Suggestibility and Hypnotizability: An Empirical Analysis. Journal of Personality & Social Psychology, 77(3), 578-587.

Carhart-Harris, R. L., Erritzoe, D., Williams, T., Stone, J. M., Reed, L. J., Colasanti, A., . . . Nutt, D. J. (2012). Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin. Proceedings of the National Academy of Sciences. doi: 10.1073/pnas.1119598109

Carhart-Harris, R. L., Kaelen, M., Whalley, M. G., Bolstridge, M., Feilding, A., & Nutt, D. J. (2015). LSD enhances suggestibility in healthy volunteers. Psychopharmacology, 232(4), 785-794. doi: 10.1007/s00213-014-3714-z

Griffiths, R., Johnson, M., Richards, W., Richards, B., McCann, U., & Jesse, R. (2011). Psilocybin occasioned mystical-type experiences: immediate and persisting dose-related effects. Psychopharmacology, 218(4), 649-665. doi: 10.1007/s00213-011-2358-5

Klavetter, R. E., & Mogar, R. E. (1967). Peak Experiences: Investigation of Their Relationship to Psychedelic Therapy and Self-Actualization. Journal of Humanistic Psychology, 7(2), 171-177. doi: 10.1177/002216786700700206

MacLean, K. A., Johnson, M. W., & Griffiths, R. R. (2011). Mystical Experiences Occasioned by the Hallucinogen Psilocybin Lead to Increases in the Personality Domain of Openness. Journal of Psychopharmacology. doi: 10.1177/0269881111420188

Smith, C. L., Johnson, J. L., & Hathaway, W. (2009). Personality Contributions to Belief in Paranormal Phenomena. Individual Differences Research, 7(2), 85-96.

Thalbourne, M. A. (2010). Transliminality: A Fundamental Mechanism in Psychology and Parapsychology. Australian Journal of Parapsychology, 10(1), 70-81.

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