I went last year on a cruise ship and it was cool. Our cab driver got us stoned all day while he showed us the sites. The weed is very good and the beaches are awesome. I am planning to go back after christmas. It is a poor country so you need to be careful but tourism is a important part of their economy. The people are friendly. You will be fine as long as you use common sense. It is no worse than mexico. Ocho Rio, Neigral and Montego Bay are the best places to stay. Kingston is the town you want to stay away from because they have a gang problem there. Check out these links, they may help
Jamaican ganja tour and
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Jamaica Tours, Guides and Vacations Ganja Fields and Marijuana Tours