Sorry to just jump in on your posts.....just wondering...has anyone ever had severe pain from their groin thru their thigh while taking fentanyl? I seem to remember having this before while I was on Percocet. Just recently got switched from morphine to Fentanyl and the leg pain is excrutiating. Today I did not replace the patch and took a morphine I had left over and Voila! No leg pain! Can this be that I am allergic?