By Malena Castaldi and Felipe Llambias MONTEVIDEO (Reuters) – Uruguay became the first country to legalize the growing, sale and smoking of marijuana on Tuesday, a pioneering social experiment that will be closely watched by other nations debating drug liberalization. A government-sponsored bill approved by 16-13 votes in the Senate provides for regulation of the cultivation, distribution and consumption of marijuana and is aimed at wresting the business from criminals in the small South American nation. Backers of the law, some smoking joints, gathered near Congress holding green balloons, Jamaican flags in homage to Bob Marley and a sign saying: "Cultivating freedom, Uruguay grows." Cannabis consumers will be able to buy a maximum of 40 grams (1.4 ounces) each month from licensed pharmacies as long as they are Uruguayan residents over the age of 18 and registered on a government database that will monitor their monthly purchases. When the law is implemented in 120 days, Uruguayans will be able to grow six marijuana plants in their homes a year, or as much as 480 grams (about 17 ounces), and form smoking clubs of 15 to 45 members that can grow up to 99 plants per year.