I have been using Diclofenac gel brand and generic for two
years regularly. There is absorption through our skin.
Possibly 5 or 10 percent of what we apply. The arthritis pain strength is 1%. In theory if you use a generous 4 gm dollop
you might absorb 4gm x .01 = 40 mg applied x 5 to 10%
works out to 2 or 4 mg internal dosing. Very low and not
very likely to create any problems. Bypassing any worrisome
stomach irritation. Most serious adverse effects quoted are for much higher oral dosage and fortunately very rare.
There was a stronger formula used to repair sun damaged skin that was often very irritating in the process.
I use it on multiple areas of tendon and ligament inflammation and it seems to help when applied several times a day. Suspect it works better for tendonitis due to the
anatomy. It is likely metabolized differently on skin rather than by mouth. House brands are least costly per ounce.