We humans have been shaped by past evolutionary processes to be very good at identifying patterns - and to enjoy doing so, such that we will spent significant investments in time and effort in this task. Pattern recognition was so important to evolutionary success back in the early days of humanity that it was acceptable to suffer the downside: our tendency to see patterns where there are none, and the limitations of our pattern recognition when applied to complex or random systems. We are adapted to pattern recognition in a "fire burns X, so it will burn Y", "the stars will do this next year as well" range of experience - we do not do well for much more complex situations.
Magical thinking - or "non-scientific causal reasoning" - is well-documented and understood consequence of the nature of our hard-wired ability with (and desire for) patterns. It can be found at the roots of magical activities in a wide range of traditions and cultures. These activities spring from common human urges, traits and societal structures, and so are remarkably similar at root, for all their varied details:
Magical thinking is a term used by some scholars to describe non-scientific causal reasoning (ie superstition). James George Frazer and Bronislaw K. Malinowski said that magic is more like science than religion, and that societies with magical beliefs often had separate religious beliefs and practices. Like science, magic is concerned with causal relations, but unlike science confuses correlation with causation. For example, someone may believe a shirt is lucky if he had won a bowling competition in it. He will continue to wear the shirt to bowling competitions, and though he continues to win some and lose some, he will chalk up every win to his lucky shirt.
According to Frazer, magical thinking depends on two laws: the law of similarity (an effect resembles its cause), and the law of contagion (things which were once in physical contact maintain a connection even after physical contact has been broken). These two laws govern the operation of what Frazer called "sympathetic magic", the idea that the manipulation of effigies or similar symbols or tokens can cause changes to occur in the thing the symbol represented. The use of voodoo dolls is a typical example of sympathetic magic. Others have described these two laws as examples of "analogical reasoning" (rather than logical reasoning).
The scientific method is the cure for problems caused by magical thinking, such as a lack of progress towards better lives, and all the limitations - dramatic or trivial - that stem from an incorrect understanding of the way in which the world works. To make progress happen, you must tackle complex systems in a methodical way: propose, explore, test, verify, record, repeat. But that requires more work than merely guessing, and so there will always be some market for those willing to take the "shortcut" to the wrong answer. When the wrong answer doesn't have clear, obvious and rapid bad consequences attatched to it, magical thinking will prosper. Such is the downside of human enonomic preferences - there is always a market for "incorrect" when "incorrect" is sold more cheaply than "correct."
So how does this fit in with the practice of medicine - in the broadest sense of the term, as any attempt to develop and apply technology or technique to health? Here's an article from way back in the Committee for Skeptical Inquiry archives:
To distinguish causal from fortuitous improvements that might follow any intervention, a set of objective procedures has evolved for testing putative remedies. Unless a technique, ritual, drug, or surgical procedure can meet these requirements, it is ethically questionable to offer it to the public, especially if money is to change hands. Since most "alternative" therapies (i.e., ones not accepted by scientific biomedicine) fall into this category, one must ask why so many customers who would not purchase a toaster without consulting Consumer Reports shell out, with trusting naivetë, large sums for unproven, possibly dangerous, health remedies.
The answer, I believe, lies in a combination of vigorous marketing of unsubstantiated claims by "alternative" healers, the poor level of scientific knowledge in the public at large, and the "will to believe" so prevalent among seekers attracted to the New Age movement.
It's a decade on from the date of writing - so much changes in detail, but people are still people. You don't have to wander far at all into the modern "anti-aging" marketplace to see magical thinking in the sales materials.
The wider business community - including a great many fraudulent and frivolous ventures - views "anti-aging" as a valuable brand and a demonstrated way to increase sales. At the worse end of the scale, this leads to snake oil salesmen, "anti-aging" cremes that may or may not make your skin look younger, and infomercials that tout the "anti-aging" benefits of exercise machines. Broadly, and very charitably, we can look at these varied definitions of anti-aging as meaning "to look and feel younger in some way" - which has no bearing on how long you live or how healthy you actually are.
Magical thinking is often accompanied and obfuscated by pseudo- or irrelevant science, so as to be made to appear more like the sort of work that comes out of the scientific community. Here is a good example of the type:
One key ingredient is a soybean cuticle extract that the company claims stimulates the body's production of a protein to slow aging. Orlane says its product is based on studies of the longevity of Okinawans, whose fish and soybean diets have been credited for the large number of centenarians on the Japanese island.
"They lived to their 100s and died wrinkle-free," said Naz Toloui, Orlane's vice president of sales and education.
Japan's Kanebo boasts an even more unusual ingredient. Its "Sensai Premier" eye cream - priced at $320 for 0.5 ounces - is infused with Koishimaru silk extract, from delicate silk cocoons that are half the size of normal silk cocoons. Kanebo, founded almost 120 years ago as a textile-manufacturing company, began producing soaps containing silk in the 1930s after noticing that silk workers' hands were soft. Kanebo claims that the Koishimaru silk extract stimulates the skin's production of hyaluronic acid, a component of connective tissue.
Those two above are examples of sympathic magic at its finest - A and B are somewhat the same, so it must work, right? Some people will believe enough in any new such proposal to spend resources, and other, better-educated people rightly estimate that they'll make money from investing in the beliefs of the the first group. Once it all gets going, you'll see a self-sustaining industry with the resources to expand the pool of consumers through (mis)education, and which comes to employ more and more true believers in key positions.
Many such interesting follies of human endeavor populate this world, growing organically from evolutionarily selected traits of the human mind. One might almost consider it a sort of species-level antagonistic pleiotropy - except that that would be magical thinking.
But none of this is going to help anyone to live a longer, healthier life. For significant healthy life extension you need the scientific method, modern biotechnology, a geared-up, dedicated and funded research and development community, and widespread recognition that the rapid development of real, modern medical science is the only viable path forward. Manipulating human biochemistry - identifying and repairing the root causes of aging - is simply too complex for any other way to succeed.