While there can be no doubt that engaging in mindfulness practices or meditation can lead to harm or unpleasant or adverse effects, currently meditation research is not in a position to provide accurate estimates how likely such experiences are or under which conditions they may occur. Publicised prevalence estimates should thus be treated with scepticism.
In a 2020 blog post, I discussed a study into potential negative side effects of the mindfulness-based stress reduction programme (MBSR). This study by Hirshberg et al. investigated data from more than 2,400 MBSR participants and concluded that – compared to no treatment – the MBSR programme prevents harm rather than leading to psychological or physical harm. Soon thereafter, another study on the topic pushed a very different message, estimating that more than 8% of people engaging in meditation will experience adverse effects.
Research finding could hardly be more conflicting! But where does this discrepancy – this obvious contradiction – come from? How can it be that one study concludes that there are no negative side effects of mindfulness meditation, whereas another study implies that one in twelve people engaging in meditation will experience some form of harm?
In this post I aim to get to the bottom of it. Having already reviewed the former study, I will now unpick the latter to find out how justified the prevalence estimate of 8.3% of adverse effects really is.
A new meta-analysis on harm through meditation
This latest meta-analysis sets out to “provide an assessment of the major categories of adverse events and its prevalence across the meditation literature” (p. 3) by covering “all types of empirical reports, regardless of their methodological approach” (p. 3). Thus, this study employed a catch all approach rather than a) focusing on a specific meditation tradition or intervention approach and/or b) restricting the analysis to methodologically robust research.
On the one hand, this catch-all approach can be a useful for getting a fairly broad indication of the overall state of affairs. On the other hand, it limits the applicability of the results because we don’t know how trustworthy results from studies with weak methodology are. Similarly, without specificity regarding the meditation approach or type of intervention, we do not know whether when and where the findings apply, if at all.
What lies behind the implication that one in twelve people who meditate will experience adverse effects? Can it really be true that one large-scale study of MBSR finds no evidence of harm whereas a meta-analysis shows a high prevalence of harm?
Figure mix-up – corrected on 10 October 2020
When delving into the data, scrutinising tables, figures and supplementary material, I realised that the figure summarising the key results was incorrect (Figure 2, p. 12). This has now been rectified. But If you accessed/downloaded the article before 10 October 2020, you are likely to have the article with the wrong figure included.
What does prevalence of adverse events mean?
The meta-analysis set out to establish the prevalence of adverse events associated with meditation. Prevalence basically means the number of occurrences of an event. Usually, a prevalence value would be related to a specific time window. Typical time windows are, for example, one year or the whole lifetime.
Lifetime prevalence specifies how many people of a population are expected to experience a certain event – often an illness – throughout their life. To give an example, a recent meta-analysis (Lim et al, 2018) studied depression in the community across 30 countries, estimating a lifetime prevalence of 10.8%. With other words, according to these data, almost 11 out of a hundred people will suffer from depression at some point in their life.
The important point to take from this is that prevalence estimates become meaningful when a time window is specified. This was not the case in this meta-analysis. Prevalence estimates are included without specifying a time window. In consequence, the 8.3% headline figure lacks specificity, limiting the potential relevance of the claim: Is it the case that if 100 people follow a guided meditation via a YouTube video once in their life, eight of them will experience adverse effects as a result? Or is it rather the case that from 100 people who enter a 10-day silent meditation retreat without much preparation, eight will experience some adverse effect during or after the retreat? Most likely, none of these two extreme scenarios is true. But, importantly, based on this meta-analysis we couldn’t tell.
What are the adverse events of meditation?
Different studies and approaches define potential adverse effects in different ways. For this study, the authors defined them as “occurrences that are harmful or distressing, though of varying levels of severity.” (p. 2). In line with this everything from a slight discomfort (or even less than that) to death is counted as adverse effect! Yes, you read correctly: death! I will return to this point in a moment.
The authors identified such occurrences by scrutinising whether a published research article mentioned any occurrence that can be construed as harmful or distressing and counted these as adverse effects of meditation. Such experiences ranged from changes in the galvanic skin response to diarrhoea to death, and anything in between.
An increased galvanic skin response does, however, not necessarily indicate discomfort or distress but can also co-occur with pleasant, exciting experiences. By itself, it is thus not suited as indicator of an adverse effect of meditation. At the other extreme, it is hard to argue how meditation would lead to death, thus counting someone’s death at a time when they participated in a meditation study as an adverse event of meditation, is doubtful, too.
It is worth considering other studies that have taken a more nuances approach when defining adverse effects. Hirshberg et al. (2020) defined harm as “outcomes worse than would have been expected in the absence of treatment” (p. 2). This definition builds on research into adverse effects in psychotherapeutic practice (Dimidjian & Hollon, 2010). To me, it seems that this latter approach yields a more realistic estimate of any risks involved in taking up or engaging in meditation.
Although almost too trivial to mention, let’s dwell on these different definitions for a moment: Living a life without engaging in meditation entails a certain risk of adverse effects. As mentioned earlier, some research suggests a lifetime prevalence for depression is around 11%. And that’s for depression only! If we accept that a certain number of people will experience something adverse, harmful or distressing also without meditation, the question shifts to asking how much the likelihood of such adverse effects is changed when we do engage in meditation.
That’s what Hirshberg et al (2020) aimed to do. Although, as pointed out by van Dam & Galante (2020) in a comment to Hirshberg et al’s study, doing so is tricky in itself, the meta-analysis by Farias et al. does not contribute anything meaningful in this respect.
Indeed, going through some of the adverse events that purportedly result from meditation, made me smile. Adverse effects from one study included rash, diarrhoea, hives, liver problems, and abdominal pain. While these experiences are certainly adverse, it is hard to claim that liver problems or diarrhoea – or any other of these symptoms on that list – can be construed as result of meditation practice. Nevertheless, this study by Dhalla et al. (2006) contributed with a prevalence estimate of around 63% to the overall prevalence rating!
Stroke and death through meditation?
But it gets even “better”: Based on reports from one study stroke and death were recorded as adverse effects. To be very clear: by counting stroke and death as adverse effects of meditation, the authors imply that engaging in meditation is a causal factor for stroke or death! I think, such claims do not require further comments.
How are the adverse effects found?
To answer this question, let us return to the study by Dhalla et al. (2006), from which diarrhoea, Iiver problems etc were extracted as adverse effects. This study was a cross-sectional survey of patients with HIV and aimed to identify adverse effects resulting from alternative/complementary treatment these HIV-patients engaged with on their own accord. Out of the 105 participants who stated that they engaged in meditation (neither type nor time specified), 63% (66 participants) also reported side effects, whereas only 51% of study participants who did not complement their therapy with meditation experienced side effects. To indicate the risks of meditation, it would have been meaningful to relate the 63% value to the base-rate of adverse events (51%). By not doing so, important information that could give us a sense of the potential elevated risk of engaging with meditation is lost and a distorted estimate presented.
Furthermore, given the specific sub-population (primarily older male, with AIDS diagnosis, with higher CD4 count and lower viral load), it is doubtful to what extent their health problems can be considered representative of the general population.
Let us look at one more example of such selection bias that distorts the result. A good example is the study by Heide and Borkovec (1983). They investigated if being exposed to a single session of progressive muscle relaxation and mantra meditation enhanced anxiety. Crucially, to be included in the study, participants had to experience “self-reported tension, anxiety, or nervousness during at least 40% of the day” and had to rate “this tension as moderate to severe“ (p. 172). With other words, only individuals who experience unusually high levels of tension or anxiety were admitted to the study. Exposing them to a single meditation or relaxation session in a laboratory context increased their tension and anxiety. This finding was recorded in the meta-analysis as a 96.7% incidence of adverse events. It was, however, not recorded that after the meditation and relaxation sessions participants had lower anxiety and tension than before. In the words of Heide and Borkovec (1983): “Pre-posttreatment rating scales and physiological measures generally displayed reductions due to treatment, despite the fact that many subjects reported increased tension during the sessions.” (p. 179)
And a final example: Williams et al (2014) reported 5 adverse events (in 108 participants). A prevalence estimate of 4.6% is included in the meta-analysis. However, in the control group a higher number of adverse events (namely 10, 6.4%) were recorded. Neither are these taken into account nor is the fact that Williams et al. classed the adverse events as unrelated to participating in the intervention.
What to make from it? Does meditation lead to harm?
In fairness, any researcher carrying out a meta-analysis depends on the available study data. The authors acknowledge the heterogeneity of available studies and – without stating this as clearly and prominently as I’d like to see – imply that their prevalence estimates are not robust enough apply them in a meaningful way. However, it begs the question how meaningful such meta-analysis is in the first place, if we cannot draw meaningful conclusions from it.
Until quite recently hardly anyone was talking about potential negative effects or any form of harm that can result from meditation. It is, thus, encouraging to see that now it is attracting more attention. Hopefully, this will allow us to move beyond headline-grabbing claims of personal disasters resulting from meditation to a more nuanced and accurate understanding of potential dangers.
Unfortunately, this new meta-analysis does not bring us closer to this goal. Some may say that after an initial over-positive embrace of meditation as psychological and therapeutic intervention, it is only right to let the pendulum swing in the other direction and exaggerate potential negative effects. This is, not my idea. First of all, criticising that a perspective is too extreme (too positive) and then engaging in extreme perspectives does not seem right. More generally, we will instil more confidence in a scientific approach when we all aim for a critical, reflected and balanced approach that expresses as accurately as possible what we currently know and do not know.
Rather than building on the unsubstantiated and prevalence estimates of adverse events this meta-analysis provides, the study should merely be taken as an appeal to improve the research, for instance by introducing standard approaches for assessing and tracking potential adverse effects.
Of equal importance is a more fine-grained consideration of meditation traditions, intervention approaches and timescales. The authors state themselves that meditations differ “Different types of meditation are likely to engage diverse cognitive mechanisms (9, 10) and have been found to be associated with contrasting neural correlates, …” (p. 2)
Meditation researchers should be aware that potential adverse experiences attributable to meditation need to be considered. To move beyond speculation a coherent way of capturing such adverse events should be included in every intervention study. Where appropriate these should be tracked over longer time periods, ideally in a fashion that allows attribution of potential causality. While implementing such assessment in well-defined intervention studies is easier to achieve (albeit not without challenges), it will be even more challenging do gather robust evidence in more ‘natural’ meditation settings.
Practitioners who offer meditation- and mindfulness-based training and programmes, will need to consider how to deal with potential adverse events. To some extent, well-established programmes such as MBSR or MBCT work towards this by routinely include pre-enrolment assessments and interviews.
For the general public and anyone interested in trying out meditation it seems important to not feel discouraged by sensationalist claims about potential dangers of meditation. However, it seems prudent to learn meditation from qualified meditation / mindfulness teachers, who should be skilled in guiding people in meditation and in observing and responding to potential challenges and adverse experiences.