How To Combat The “Illusion Of Causality” That Contributes To So Many Healthy People Taking Multivitamin Pills They Don’t Need

GettyImages-537472788.jpgBy Matthew Warren

Millions of people around the world spend time and money on healthcare remedies that mainstream science considers ineffective (in the sense of being no more effective than a placebo), like homeopathy and acupuncture. A study published recently in Psychology and Health investigated how to address this issue in the context of multivitamins, which evidence suggests provide no benefit for healthy people – and may even cause harm in some contexts. 

Despite this research evidence, huge numbers of healthy people take multivitamins because they appear to be helpful. Scientists refer to this as the “illusion of causality”: when someone takes a vitamin and then their cold goes away, for example, they may believe it was the vitamin that cured them, even though they would have recovered just as quickly anyway. Past research has shown that simply giving people the raw outcomes of clinical trials that show remedies to be ineffective does not necessarily help combat this problem, perhaps because the data can involve large numbers and complex findings, which are difficult for the public to interpret. 

Douglas MacFarlane and colleagues from the University of Western Australia have explored how to better inoculate people against this illusion. The researchers report that people need to be told clearly about the proportion of people who benefit from the remedy versus taking a placeboand this data has to be accompanied by a scientific explanation for why the remedy is ineffective.

The researchers recruited 245 undergrad participants and split them into several groups, which were each given different levels of information about the effectiveness of a multivitamin. At one extreme, a control group received no information about the number of people who benefited from the remedy, and was simply told that there was insufficient evidence to make a recommendation for or against using it. At the other extreme, another group was told that 3 out of 4 people benefitted from the pills, but that 3 out of 4 people also benefitted from a placebo, so the evidence showed that the remedy doesn’t have any health benefit. This group was also given a scientific explanation for why this should be: healthy people already receive enough vitamins in their diet.

There were also various intermediate groups, such as one that received information about the proportion of people who get a benefit from the pills, but no information on the effects of placebo, and another that received information about the pills and placebo, but no scientific explanation. 

Afterwards, all participants were asked how much they would be willing to pay for a tube of the multivitamins. The only group who showed a reduced willingness to pay for the pills was the one given full information on the pills’ efficacy compared with a placebo and the scientific explanation of why they are not effective. 

The results suggest that simplified frequencies showing how many people have and haven’t benefited from a remedy compared with placebo could help prevent the illusion of causality. This strategy could be used by health authorities to assist people making healthcare decisions, say the authors. At the moment, they write, bodies like the National Institutes of Health in the United States often frame disclaimers about ineffective remedies in diplomatic language about “insufficient clinical evidence”, rather than giving people this kind of simple, explicit data.

Importantly though, the new findings suggest these frequencies are only useful when given alongside a scientific explanation. “This component may serve to fill the mental gap created when a prior belief is challenged by scientific evidence,” write the authors. 

This conclusion comes with a hefty caveat, however. Because only one group was actually given the scientific explanation, it remains unclear based on the current results whether the explanation and the simple frequencies are both necessary. A scientific explanation about why a remedy is ineffective could, in theory, reduce a person’s willingness to pay regardless of how much they know about the underlying data. Of course, scientific explanations alone can be pretty unsuccessful at changing people’s minds, so this possibility seems unlikely – but it would be nice to see this question incorporated into the design of a future study. 

Reducing demand for ineffective health remedies: overcoming the illusion of causality

Matthew Warren (@MattbWarren) is Staff Writer at BPS Research Digest

10 thoughts on “How To Combat The “Illusion Of Causality” That Contributes To So Many Healthy People Taking Multivitamin Pills They Don’t Need”

  1. But, the placebo effect is “real”. It’s almost as if there is something to this “mind over matter” craziness.


    1. The placebo effect exists for many people but apparently not for me. I get no pain relieving effect from paracetamol, which allegedly for many if not most people is little more than a placebo. At the same time there are pet owners who say that their pets have benefited from such treatments as homeopathy despite the pet not knowing, obviously, that it is being treated. Placebo treatment needs a lot more study, including study of people who fail to respond to placebos.


      1. A possible explanation for the placebo effect lies in Cartesian Dualism.

        In dualism the mind is an immaterial “thing” that interacts with material reality via the brain and nervous system. If we consider the mind as a CPU (central processing unit) then the brain is akin to a device controller or sensor suite. Thus, a thought can cause changes in body chemistry. The major argument against dualism

        “is with regard to causal interaction. If consciousness (the mind) can exist independently of physical reality (the brain), one must explain how physical memories are created concerning consciousness”.

        This argument is succinctly answered by Eugene Wigner:

        “When the province of physical theory was extended to encompass microscopic phenomena through the creation of quantum mechanics, the concept of consciousness came to the fore again. It was not possible to formulate the laws of quantum mechanics in a fully consistent way without reference to the consciousness.”


    2. This might apply in a very limited number of situations, but there are many placebo effects that nobody would consider “real.” In the example here, many people take vitamins for a cold, then get better. It’s not because of some “mind over matter” effect—it’s because people get better naturally, but only attribute the cause to vitamins when they take them.

      They may also make errors in self reporting when the placebo is present. E.g., reporting that the cold went away because they’re not sneezing any more, despite the presence of other symptoms, whereas without the placebo that made them think the cold should have gone away, they would have considered those other symptoms a sign of the cold continuing.

      Even in the rare cases where the mind really does create an effect out of nothing, it doesn’t mean placebos have a use. The thing with a genuinely effective treatment is that it also has all those placebo effects, PLUS the actual effect.

      Add in the risk of foregoing real treatment and using a placebo instead, and the whole “what’s the harm?” argument becomes outright dangerous.


  2. People are primed for this by advertising. Newspapers, and online sites promote this nonsense constantly. Many credible appearing sites endorse the Placebo Effect. Americans spend billions of dollars every year on vitamins and quack cures, it is a huge profitable industry. There are plenty of physicians who actually endorse this nonsense, because it is profitable. The Anti Vaxx Movement should have given someone a heads up, because it is not harmless, it can be deadly. As long as there is a profit in spreading lies and misinformation, this stuff will proliferate.


  3. Or perhaps people have experienced improvement of health and changes from taking their various supplements and herbs. For instance taking zinc relieved dry skin. Testing for Vitamin D, being deficient and taking vitamin D and experiencing better mental health and relief from depression. Taking milk thistle and various other liver support and pro-biotics and stopping chronic diarrhea and whitened eyes. Taking vitamin C and zinc and stopping colds and having far fewer colds, perhaps for years. People are their own experiments. For instance, using meditation techniques and becoming calm and poised and more loving. If people have experienced their own improvements to their own supplement experiments, you aren’t going to dissuade them. If they or their children or expended family members or friends have had adverse and severe reactions to vaccinations, you aren’t going to persuade them to believe “resort to authority” arguments and not their own eyes and experiences.


  4. To say, without any evidence, that acupuncture is ineffective and no better than placebo while ignoring the complexity of acupuncture research, placebo research, and all the evidence that acupuncture actually is more effective than no treatment or placebo/sham needling is highly disingenuous and misguided.

    Even the NIH website on acupuncture refers to comprehensive systematic reviews and meta-analysis that point to effectiveness for certain types of chronic pain, stating:

    “Results from a number of studies suggest that acupuncture may help ease types of pain that are often chronic such as low-back pain, neck pain, and osteoarthritis/knee pain. It also may help reduce the frequency of tension headaches and prevent migraine headaches. Therefore, acupuncture appears to be a reasonable option for people with chronic pain to consider. However, clinical practice guidelines are inconsistent in recommendations about acupuncture.

    The effects of acupuncture on the brain and body and how best to measure them are only beginning to be understood. Current evidence suggests that many factors—like expectation and belief—that are unrelated to acupuncture needling may play important roles in the beneficial effects of acupuncture on pain.” (

    New studies have begun to separate the placebo effects (psychosomatic) from the actual effects (Makary et al., 2018) revealing that the complex nature of acupuncture treatment. Acupuncture is not merely the stimulation of local and CNS responses leading to a cascade of healing effects (Adrian, 2009), but as Makary et al. have continued to reveal, it is a comprehensive treatment involving patient/provider interaction, direct touch, and the additional neurophysiological responses from needling, all of which contribute to broad effects including localized changes (e.g. vasodilation, release of neuropeptides, inflammatory/immune responses, etc.), spinal segmental signaling, endogenous opioid release, neuromuscular/myofascial mechanical responses, and the CNS responses/changes (Corradino, 2017).

    To ignore the current evidence for acupuncture’s effectiveness in addressing certain chronic disease patterns merely because sufficient evidence or quality research has yet to arrive at a full understanding of the underlying mechanism is laughable considering the mountains of research already establishing the physiological and neuromuscular mechanisms, and clinical effectiveness.


  5. I would have thought another ‘hefty caveat’ of the conclusion would have been to do with the sample – 245 split into several groups seems a pretty small sample size to make solid conclusions. also they were all under graduates who may well respond differently to scientific explanations than the population at large.


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