A state senator wants to impose Massachusetts' 6.25 percent sales tax on medical marijuana purchases and assess soon-to-be opened dispensaries a 4 percent surcharge on their revenues.

Sen. Brian Joyce, a Democrat from Milton, proposes money generated from the marijuana taxes be designated to a new state fund for substance abuse treatment programs. The amendments are among hundreds filed by senators in advance of Wednesday's start of debate in the Senate on a House-approved $36 billion state budget.

But Matthew Allen, of the Massachusetts Patient Advocacy Alliance, says it would be ``inappropriate'' to impose taxes on medicine chronically sick patients need. Connecticut, Rhode Island and Maine subject medical marijuana to the sales tax. New Hampshire does not have a sales tax and Vermont has not said it will tax the drug.