Short answer
A cannabis transdermal patch carries cannabinoids through the skin and into the bloodstream. It bypasses the stomach and liver. Onset runs about 15 to 60 minutes in most manufacturer labels. Effects last 8 to 12 hours. No cannabis transdermal patch holds FDA approval. All U.S. patches sold today are state-licensed products.
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Skin as a delivery route
Skin blocks most molecules. The outer layer, the stratum corneum, is the main barrier. Cannabinoids are fat-soluble and heavy, so they cross this layer at a slow rate. A patch solves this with two parts: a drug reservoir and a permeation enhancer. The enhancer loosens the lipid structure of the stratum corneum for a short time. The cannabinoid then diffuses into the dermis, where capillaries absorb it.
Matrix and reservoir designs
- Matrix patch: cannabinoid is mixed into an adhesive polymer. Release is steady and the patch is thin.
- Reservoir patch: cannabinoid sits in a gel or liquid pocket behind a rate-controlling membrane. Release is flatter over time.
Onset, peak, and duration
- Onset: 15 to 60 minutes on most labels. Measured plasma levels can lag this.
- Peak: often 1 to 3 hours after application. Published human data are limited.
- Duration: 8 to 12 hours per patch.
- Bioavailability: estimates for transdermal THC sit near 10 to 20 percent. Oral THC runs about 4 to 12 percent.
Steady plasma concentrations in human studies are low, in the low nanograms per milliliter range. A patch does not produce the sharp peak of inhalation.
Transdermal compared to topical and oral
A topical product stays in the skin. It acts at the site of application and enters blood in small amounts. A transdermal patch is designed to enter blood. Oral edibles pass through the liver, where THC converts to 11-hydroxy-THC. That metabolite drives the strong edible high. Transdermal delivery avoids first-pass liver metabolism, so the metabolite profile differs.
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Dose and labeling
Most THC patches list 10 to 20 mg per patch. CBD patches vary more. Absorption depends on skin site, skin temperature, body fat, and hydration. Labels list total cannabinoid content, not delivered dose. Two people using the same patch can absorb different amounts.
Limits and risks
- Skin irritation and contact dermatitis from adhesives are common.
- Heat raises absorption. Saunas, hot tubs, and fever can increase dose.
- Patches are hard to titrate. Once applied, the dose cannot be stopped fast.
- Drug interactions are not well studied.
Regulation
The FDA has approved no cannabis transdermal patch. Approval covers only three cannabinoid drugs: dronabinol, nabilone, and cannabidiol. Patch makers in state markets follow state testing rules for potency, pesticides, and solvents. Those rules differ by state.