Mary’s award-winning transdermal patches are born out of a commitment to accurate dosing through an advanced delivery method. The discreet 2×2″ squares simply adhere to any veinous part of the skin for 8-12 hours of unsurpassed systemic wellness benefits. 20mg THC / Onset: 15 – 30 minutes / Duration: 8 – 12 hours / Dosage: 1 – 4.