For years, we have offered topical cannabis preparations, which are considered non-psychoactive because a topical medication is intended to have an effect at the site of application. The use of topical medications does not result in significant drug concentrations in the blood and other tissues. Examples of topical medications include antibiotics for skin infections, corticosteroids for skin irritation, and some anesthetics. Topical cannabis can be excellent for eczema and psoriasis, minor burns, irritation, and rashes / itching, and many patients report localized pain relief as well.
Transdermal medications, like the new products from Mary’s Medicinals, are absorbed through the skin and into the bloodstream. When a medication is applied to the skin, whether the effect will be local (in the tissue beneath the site of application), or systemic depends on the preparation, and factors such as molecule size and solubility. To work in a transdermal patch, a medicine must be lipophilic (fat-soluble) and potent enough that a low dose will work, so cannabis is ideal in that respect.
Transdermal delivery is quite different from other methods of medicating (see chart below for comparison). Effects can be felt as quickly as a few minutes after applying the patch, and last up to 12 hours as long as the patch remains in place. The patch provides a controlled release of the medication, so the effects stay at a constant level rather than the “peaks and valleys” of other methods of administration. Transdermal dosing is also different from other methods. Due to the high bioavailability, a 10mg patch may deliver as much medicine to the bloodstream as an 80mg edible dose. Bioavailability is the fraction of an administered dose of unchanged drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%, and the transdermal delivery system delivers medicine to the veins, so it is considered the same as intravenous administration.