This can occur because the legalisation of marijuana is also likely to increase the for marijuana (independent of ) because many new consumers will enter the no longer fearing the prospect of committing a crime for possessing/consuming marijuana. This will cause the demand curve to shift to the right, and to the extent that the demand impact outweighs the supply impact (i.e. the effects of a shift of the demand curve to the right outweighs the effects of a shift of the curve to the right), the overall effect will be to see a higher price for marijuana.