Avorn (2004) reports:
In a former British colony, most healers believed the conventional wisdom that a distillation of fluids extracted from the urine of horses, if dried to a powder and fed to aging women, could act as a general tonic, preserve youth, and ward of a variety of diseases. The preparation became enormously popular throughout the culture, and was widely used by older women in all strata of society. Many years later modern scientific studies revealed that long-term ingestion of the horse-urine extract was useless for most of its intended purposes, and that it causes tumors, blood clots, heart disease, and perhaps brain damage.
The former colony is the United States; the time is now; the drug is the family of hormone replacement products that include Prempro and Premarin (manufactured from pregnant mares' urine, hence its name). For decades, estrogen replacement in postmenopausal women was widely believed to have "cardio-protective" properties; other papers in respected medical journals reported that the drugs could treat depression and incontinence, as well as prevent Alzheimer's disease. The first large, well-conducted, controlled clinical trial of this treatment in women was not published until 1998: it found that estrogen replacement actually increased the rate of heart attacks in the patients studied. Another clinical trial published in 2002 presented further evidence that these products increased the risk of heart disease, stroke, and cancer. Further reports a year later found that rather than preventing Alzheimer's disease, the drugs appeared to double the risk of becoming senile.
Armstrong (2006) adds:
The treatment seemed to work because those who used the drug tended to be healthier than those who did not. This was because it was used by people who were more interested in taking care of their health.
Absent any other prior, why would you use anything other than "My body will react to hormones the same way most other people's bodies react to hormones"?
And you can't self-experiment on risk of a heart attack. Your only endpoint is "I had a heart attack" or "I didn't have a heart attack", and even if you don't mind getting your experimental result exactly one instant too late to help you, with a sample size of one you can't draw any conclusions about whether taking HRT for ten years contributed to your heart attack or not.
And probably the most important reason is that medicine is weird. Even when the smartest people try to predict results that should be obvious, they very often get them wrong. "Based on what I know about the body, this sounds like it should work" is the worst reason to do anything. I know that sounds contrary to Bayes, but getting burned again and again by things that sound like they should work has recalibrated me on this one.
If you're saying that you have unusual incentives here - eg that you value the possibility of adding to your natural lifespan enough that you're willing to accept a small risk of subtracting from it and a large risk that you're wasting time and money, that's fair enough.
First, because I am not absent other informational priors. I have a lifetime of informational priors about my own body. I also have access to pubmed, wikipedia, my 23andme genomic data, my personal medical history, my family's medical history, and lab testing services that can take accurate measurements of me.
There are no clinical trials that have controlled for that information.
Second, becau... (read more)