Man, did I ever! Started with the 100mg size; about four hours later, after the date left and I'd gone to bed, I woke up and could barely breathe. Almost went to emergency room; headaches for the rest of the night. Cut the dose to 50mg the next time; breathing was better but still the headaches. Down to 25mg - hardon is as stiff and longlasting as ever, but no more headaches. Was around someone doing poppers, though, and that nearly made me pass out; the warnings are true; DON'T go near poppers if you are on Viagra; it will do serious damage....