Scientists found that mice lacking the CB-1 and CB-2 receptors had exacerbated inflammatory reactions in the skin and extreme skin hypersensitivity. They also found that mice with abnormally increased levels of anandamide (the naturally occurring cannabis like substance) had decreased inflammation of the skin. They also showed that chemicals that would block the effects of marijuana on the CB-1 and CB-2 receptors would result in more skin sensitivity. From these experiments with mice, it appears that activating the CB-1 and CB-2 receptors would reduce the symptoms of rashes similar to poison ivy. As a result, scientists have an incentive to design a molecule similar to marijuana that may be a safer alternative to using marijuana in its more traditional forms.

I hope I have shed a little light on the use of marijuana for medical purposes, more specifically for allergic contact dermatitis. You should certainly not attempt to treat poison ivy with marijuana and I am not promoting the use of marijuana unless you are under medical supervision. As of now, if you have poison ivy, consult your dermatologist and use the prescribed oral and topical steroids and antihistamines.