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Ineffective traditional remedies are more likely to spread and be used than effective medical therapies because their ineffectiveness prolongs use that can be uncritically copied by others, new research reveals. The surprising counter-intuitive finding could account for the prevalence of largely unproven traditional remedies and complementary medicines that have global annual sales estimated at US$60 billion.

The successful spread of ineffective remedies is especially suited to chronic, non fatal diseases because they provide more opportunities for others to observe and copy self medicating behaviours. An international research team led by UNSW evolutionary biologist Dr Mark Tanaka used mathematical and computer modelling to reach their conclusions.

Their findings are published in the latest online issue of the PLOS See From Traditional Medicine to Witchcraft: Why Medical Treatments Are Not Always Efficacious. http://www.plosone.org/article/info:doi/10.1371/journal.pone.0005192

Their model is relevant to people who seek and acquire remedies, be they traditional remedies or medical/over the counter drugs that are easily obtainable. The researchers assumed that sick individuals initiate new treatments by observing others and abandon treatments if their disease/illness continues. They also assumed that people have no direct way of telling whether a treatment is effective or not.

The finding that superstitious treatments can easily spread is supported by reports of bizarre treatments for conditions such as leprosy (treated with a drink made of rotting snakes), syphilis (treated by eating a vulture), poisonous snake bites (apply ‘guaco' leaves, poisonous lizard skin or snake's bile), dog bites (drink tea made from the dog's tail) and scorpion stings (tie a scorpion against the stung finger).

The analysis also helps explain the persistence of veterinary remedies such as ‘firing' (cautery) of working horses, employed for millennia as treatment for lameness, where recovery is rare, and still widely practiced in many countries in spite of trials establishing its ineffectiveness.

"Low-efficacy practices sometimes spread because their very ineffectiveness results in longer, more observable demonstration and a larger number of ‘converts', which more than compensates for greater rates of abandonment," says Dr Tanaka. "In contrast, increased retention of an effective treatment is also associated with reduced demonstration of the practice."

In other words, the spread of effective medical therapies is retarded by their success: their efficacy means they are less likely to be observed and replicated, and therefore given credit for curing disease/sickness. According to the model, this outcome is most likely to occur in scenarios involving a single bout of illness and treatments restricted to sick individuals.

The researchers predict that the quality of treatments that spread successfully hinge on two issues: rates of recovery from illness and abandonment of the treatment. Therefore, diseases involving high-recovery and low-abandonment favour superstitious/ineffective treatments, while diseases involving low-recovery and high-abandonment favour efficacious treatments.

"'Magical' or superstitious treatments are likely to find favour for conditions that resolve spontaneously, rarely re-occur, and where people look to advice from people who are currently experiencing a bout of illness, rather than at some time in the past," Tanaka says.

The researchers say that their computer models are relevant to any socially learned practice that is thought by a user to remedy their medical condition, through aiding recovery, reducing suffering, or reducing the probability of relapse, irrespective of whether or not the treatment actually does bring about the improvements in condition assumed by the user.

"The treatments include modern/established medical practices, complementary medicines, traditional medicines and alternative medicines," say the authors. "The models also potentially apply to instances of witchcraft, shamanism and magic in which the ‘treatment' is believed to combat perceived underlying ‘supernatural' causes of disease (e.g. the curse of a jealous neighbour, or a haunting by the ghost of an ancestor), so long as there exists a physical ailment in the user, and the treatment propagates through cultural transmission."

Media contact: Dan Gaffney - +61 411 156 015