About a year ago there was a rash of postings on Nutrasweet and its "blocking" effect on sinemet. Several anecdotal instances were related about the adverse effect of taking the medications with nutrasweet. The opinions expressed at that time was that is was the phenyalanine that caused the problem. Essentially all the diet drinks have nutrasweet in it. I believe Tab contains sacharine. There was also a long post at that time about other ill effects of nutrasweet. Perhaps there is something in the archives. Barbara was a big user of diet drinks. She went off them and noticed a difference. Several months later she tried one again and had the same adverse reaction. So far it is all anecdotal - but why take a chance? Allan