Like MrsD said, placement is key. I have Small Fiber PN and it's mostly in my feet. I use a half patch (or full patch) on each foot. High on the achilles tendon or the top of the foot near the ankle bone seem to be the best spots.

They were tested safe for 12 hours on/12 hours off, but no more. My Pain Specialist stated that 14-16 hours is fine, but not to get any closer to 24 hours than that for the reasons stated above.