R.I. Gen. Laws § 44-70-4: Exemptions.

The state cannabis excise tax and the local cannabis excise tax provided by this chapter shall not apply to the sale of cannabis or cannabis products by a medical marijuana treatment center as defined in § 21-28.11-3 to a primary caregiver, to a qualifying patient as defined in § 21-28.6-3, cardholder, compassion center cardholder, or authorized purchaser pursuant to chapter 28.6 of title 21.