I'd start by showcasing the war on drugs, specfically, medical marijuana and the money thats wasted on the raids. From there you could touch on the medicinal benefits of cannabis like what kind of people it helps, how its helps them, the ways to take your medication. Since its a persuasive paper I would focus on the TRUE facts of marijuana and help people see that the government is blinding them.
Dunno if it helps but there ya go.