I had terrible back pain and asked the pharmacist about icy hot patches. He told me NOT to use them because they are medicated, but that I could use deep relief ones because it was just menthol. So I would double check with your doctor before you use it. Especially on your stomach.
I use a regular heating pad on my back most nights to relax. Seems to help and definitely not dangerous!
My doc says tiger balm is safe. She even recommended it to use on my forehead for headaches.
She also said a heating pad on the back is okay, just be careful not to burn yourself