Illegalizing this drug will greatly increase its price. First, supplies will only be willing to sell the drug at a much higher price because of the added risk of getting caught. Second, in the short run demand might be more inelastic because of the strong dependence on the drug. People will be more willing to pay the higher price because of their dependence.
However, in the long run demand will greatly be reduced because of alternative options. Spice is currently a supplement good to Marijuana. The current demand for Spice is high because it is legal and at a relatively low price compared to Marijuana. Now that Spice is illegal the demand for Marijuana will go up.