R.I. Gen. Laws § 44-49-12: Payment due.

(a) Stamps affixed. When a dealer purchases, acquires, transports, or imports into this state controlled substances on which a tax is imposed by § 44-49-9, and if the indicia evidencing the payment of the tax have not already been affixed, the dealer shall have them permanently affixed on the controlled substance immediately after receiving the substance. Each stamp or other official indicia may be used only once.

(b) Payable on possession. Taxes imposed upon controlled substances by this chapter are due and payable immediately upon acquisition or possession in this state by a dealer.