It's a funny thing about clinical trials: they're set up so that all the subjects taking the drug in question are totally healthy in every other respect and on no other medications. It's the only way to see if the drug has an effect, but as soon as people start taking it in the real world, well...let's just say that most patients don't measure up to the pristine condition of clinical subjects. There are number of factors at work: The average 70-year-old is on seven medications. Many people are on antidepressants more or less continuously. And each of us, by our genetic background, has a slightly different response to a drug. The database where the FDA keeps the reports doctors make of patients' unexpected reactions to drugs is a bit of a mess, full of anecdotes and incomplete patient data. However, using algorithms that consolidate all the patients most similar to each other and run comparisons, scientists writing in Science Translational Medicine have managed to pinpointed hundreds of unexpected drug side effects, as well as interactions between drugs. The most notable interaction they found was that people taking selective serotonin reuptake inhibitors, a very common class of antidepressants, at the same time as thiazides, which treat high-blood pressure, were significantly more likely to develop a heart condition called long QT than people taking either one alone. Long QT can cause fainting, seizures, and sudden death. To double check that the effect was real, they ran an analysis of the medical records of patients at the Stanford hospital. The effect appeared there too. The scientists present their technique as proof that you can get decent information from the adverse reaction database. They've made their own databases publicly available: here's one that shows possible unforeseen side effects for 1,332 drugs, and here's another that shows the interactions of 52,922 pairs of drugs (both are zipped Excel files). You're unlikely to be able to see much without statistical tools, since the databases are intended for other researchers, but it's an interesting peek nevertheless.