Most drugs don’t work…
Posted by medconsumers on May 15, 2011
“Most drugs don’t work on most patients.” When I first read this statement many years ago in the British Medical Journal, a light bulb went off. I’d been a medical writer for a long time and knew it to be true. Yet I had never seen prescription drug effectiveness summed up so accurately. In a medical journal, no less! Unfortunately, drug study results are routinely reported in statistical terms known to make the drug’s benefit appear larger than it really is. More on that later.
The trigger for my light bulb moment was a 2003 editorial entitled, “Drug Don’t Work” by Richard Smith, MD, who explained, “This is of course no news to doctors. Anybody familiar with the notion of ‘number needed to treat’ (NNT) knows that it’s usually necessary to treat many patients in order for one to benefit. NNTs under 5 are unusual, whereas NNTs over 20 are common.”
The latest research, however, indicates that Dr. Smith may have overestimated physician understanding of medical statistics. A new Cochrane review of all relevant studies found that the most common statistical terms for expressing drug study results—in medical journals and the media—are misunderstood by doctors and consumers alike. In fact there was no difference in understanding between physicans and the lay public.
For the Cochrane review entitled, “Using different statistical formats for presenting health information,” the authors identified the 35 best studies designed to evaluate how well people understood the different ways of expressing the same study results. This review came down in favor of absolute risk reduction rather than relative risk reductions (RRR), as described below:
“You read that a study found that an osteoporosis drug cuts the risk of having a hip fracture in the next three years by 50%. Specifically, 10% of the untreated people had a hip fracture at three years, compared with 5% of the people who took the osteoporosis drug every day for three years. Thus 5% (10% minus 5%) less people would suffer a hip fracture if they take the drug for 3 years. In other words, 20 patients need to take the osteoporosis drug over 3 years for an additional patient to avoid a hip fracture. ‘Cuts the risk of fracture by 50%’ represents a relative risk reduction. ‘Five per cent less would suffer a fracture’ represents an absolute risk reduction. ‘Twenty patients need to take the osteoporosis drug over 3 years for an additional patient to avoid a hip fracture’ represents a number needed to treat.”
To people without statistical training—and that includes most physicians—the “cuts your risk by 50%” RRR example appears more impressive. And too often this is the sole way drug study results are described in medical journals, as well as ads aimed at physicians and the general public. Rarely is it explained that the 50% simply represents the difference between the treated and the untreated.
Here’s a real world example: Your doctor says, “You have mild hypertension and should go on a blood pressure lowering drug for the rest of your life because it will cut your risk of stroke by 50%.” Sounds good, maybe even worth the risk of sexual dysfunction and depression—two common side effects of anti-hypertensives. But here’s the other side of the story: A person with mild hypertension has only an infinitessimal chance of having a stroke, so the drug will reduce that infinitessimal risk by 50%
The common usage of RRR comes from the biostatisticians and the methodologists whose job it is to determine whether studies are conducted rigorously and results reported accurately. The fact that the Cochrane Collaboration’s own biostatisticians and methodologists are concerned enough to have produced this new review signals some recognition that it’s time for a change. (Long overdue, given that the sole use of RRR serves the pharmaceutical industry’s interest.) The Cochrane Collaboration itself has produced too many drug reviews with results expressed solely as RRR. Here’s one improvement under consideration because it is better understood: 100 of 1,000 untreated people will have a hip fracture in the next three years; 50 of 1,000 people taking an osteoporosis drug will have a hip fracture in the next three years.
The most easily understood way of expressing “most drugs don’t work on most people” can be found at this website: www.TheNNT.com Say, you are suffering from acute sinusitis but wary of taking an antibiotic for this distressing condition. You want to know how well the drug is likely to work and the likelihood of harm. TheNNT.com shows that 93% will not benefit from antibiotics; nearly 7% saw a faster resolution of their symptoms; and just over 1% were harmed by the antibiotics (e.g., diarrhea, vomiting). Even more interesting, four out of five people (in the placebo group) got better without antibiotics.
Maryann Napoli, Center for Medical Consumers(c)