Observational Studies

We have been evaluating reports that taking an SSRI antidepressant could increase the risk of osteoporotic fractures. These are all from observational studies. No one has randomly assigned depressed patients to an SSRI or a placebo, followed them for 10 or 20 years, and then checked their bone mineral density and history of fractures. And that’s too bad, because that is the only way we would ever really know if the drugs cause fractures or not.

The problem with observational studies is that the people we are observing may be different from whomever we are comparing them with, no matter how carefully we choose the comparison group. Patients once diagnosed with depression and treated with an SSRI for a period of years are different from people who were never depressed, and are even different from people who are or were depressed, but were not treated with an SSRI for years. Depressed people, for example, may not eat properly, may not exercise enough, and when they do go outside, may not notice the patch of ice on the sidewalk in time to avoid slipping on it and fracturing their hips. On the other hand, no increase in fractures or decrease in bone mineral density has been detected in depressed patients treated with tricyclic antidepressants. That’s a fairly good comparison group, but it’s still not a substitute for a randomized controlled trial.

So the best we can do is examine the strength and plausibility of the association between the alleged perpetrator and the effect. Some associations are so strong that causality can be assumed. Cigarettes and lung cancer, for instance. The association between SSRIs and fractures is nothing like that. Is it plausible? Yes, because there are serotonin receptors in bone. So what should we do with our patients, particularly postmenopausal women, who have been taking SSRIs for years? I’m not sure we’ll be able to answer that question to everyone’s satisfaction, including our own. The experts in the ivory towers may say stop the drugs and let the patients kill themselves, or screen them every 10 minutes for changes in bone mineral density and try to get the insurance companies to pay for it. The people in practice whose patients are doing well on the drugs will try to close both ears, and perhaps they should. We’ll see what we can do with all this in an upcoming issue of The Medical Letter. Watch your newsstand.

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