"after 2 years of pain after my total knee replacement , i was prescribed every narcotic under the sun, would work for 1-2 weeks then back to pain. i finally went to a pain management doctor and he prescribed the 1.3 flector patch. within the first 30 mins experienced relief. i wear two of them one on either side of the knee. i have been on them for one month, i use them for about 10 hrs a day. the only bad side effect i have experienced is massive weight gain. about 15 lbs in only one month. it does warn you on the label about possible fast weight gain. i have always maintained my weight by give or take 5 lbs...but 15lbs in 1 month is absurd."