I know several folks who are taking multiple prescriptions and over the counter drugs. You really need to be careful and make sure your Primary Care Physician is aware of all medicines you take. One way to help is to use a Pharmacy that detects drug interactions, but that does not take into account over-the-counter interactions. http://www.nytimes.com/2007/09/18/health/18brod.html?ei=5090&en=c59532de54be267b&ex=1347768000&adxnnl=1&partner=rssuserland&emc=rss&adxnnlx=1190399828-dXM+L/f5oWHrdAsqJ5PJNQ
A Day in the Life of a Presson... 
You really need to fill all of your medications at one pharmacy, most PCP’s, even good ones, don’t know enough about pharmacology to really be the guardian of medication interactions. Keep a written list of your prescriptions to give to every pharmacy you use; that way they can check and you wont forget what you’ve been presribed. (If you need a list you need to reassess your health 🙂 and your PCP probably.) You should purchase a drug book and look things up for yourself also. You would be surprised at the side effects of most medications!!! Whenever possible avoid all medications and try to find non-medication cures for your ailments. Almost always diet and excercise are the answer. Although those of you who know me know this is not as easy to do as it is to say!
the article mentions using a single pharmacy (not always possible when long-term Rx comes from mail order and short term from a local favorite source) and ensuring that the each prescribing physician is aware of both Rx and OTC medications (including “supplements” and non-traditional nutrients, e.g., herbals). It says if the physician isn’t sharp to ensure that the pharmacist is aware of each item – but how does one know whether the physician is aware of each item on your list? I think it makes sense to do both the belt and suspenders, and work with both the pharmacist(s) and the physicians.