The use of transdermal patches within human medicine is very popular for people who may want to quit smoking, relieve pain and even to replace hormones. Can these drug patches work for our pets? Transdermal drugs for animals are very similar to those used for humans. In some cases like fentanyl, the pain killer, it is identical. The drug is administered through the patch which is applied to a saved area of your pets skin, thus enabling the drug to reach the bloodstream across the skin (transd.