Had a medication give you symptoms not listed on their side effects?

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For years I took one of those 24 hour antihistamines for allergies as prescribed by an allergist, and then started getting symptoms that were not originally on the manufacturer's warnings for the medicine. It became important for me to check out all my medicines due to the symptoms and sure enough nothing was mentioned in the side effects about the ones I had. Of course, I talked to my doctor and they thought I had developed a new condition. So, I decided by the process of elimination, to discern which medication might be causing the problem. I finally discovered the one. That medication now carries a warning about the symptoms I had, rapid heart beat or irregular heart beat, but it did take 10 years before they had enough information to caution people. Long term, daily use of it, had created a problem. When I quit the medicine for some time, the symptoms evaporated. I no longer take that medication on a daily basis but as needed, and that is not the way I was told to take it originally. It is my belief that the problem only occurred because of the regular daily use of the medicine. Have you ever had a problem that could be attributed to a medication but isn't listed as a side effect?