Figure. Concentration-dependent activation of CNR1 by Δ9-THC. Reporter cells were transfected with the expression plasmid for can­nab­i­noid receptor 1 (CNR1) and treated with various concentrations of Δ-9-tetra­hydro­can­nab­i­nol (Δ9-THC). Data points shown are the mean ± SEM of an experiment performed in triplicate, and the curve is a fit to Hill equation with an EC50 of 4.1 nM.