Uruguay's House of Representative is preparing to vote on a bill to legalise marijuana on Wednesday.
If passed by the House and the Senate, Uruguay will become the first country to legally regulate the production, distribution and sale
The law is backed by the government of President Jose Mujica, which says it will remove profits from drug dealers and divert users from harder drugs.
Under the bill, only the government would be allowed to sell marijuana.
The state would assume "the control and regulation of the importation, exportation, plantation, cultivation, the harvest, the production, the acquisition, the storage, the commercialization and the distribution of cannabis and its by-products".
Buyers would have to be registered on a database and be over the age of 18. They would be able to buy up to 40g (1.4oz) per month in specially licensed pharmacies or grow up to six plants at home.
Political hot potato
Fifty representatives out of the 99 sitting in the House will have to vote in favour of the bill for it to go to a second vote in the Senate.
While the governing Frente Amplio (Broad Front) coalition has a majority of one in the House, Frente Amplio Congressman Dario Perez has threatened to vote against the bill.
Three opposition representatives have expressed support for the bill, but it is not clear whether they will vote accordingly
President of the House of Representatives German Cardoso predicted it would be "a long session, in which many representatives will want to take part".
The bill was unveiled last year by Defence Minister Eleuterio Fernandez Huidobro who argued that "the prohibition of certain drugs is creating more problems for society than the drugs themselves... with disastrous consequences".
But Mr Cardoso of the opposition Colorado Party said that "in no country in the world has the consumption of drugs been reduced through legalisation".
Another opposition politician, Richard Sander, said that even if the law made it through both chambers, he would launch a petition to have it overturned.
The vote comes amidst a vociferous debate about drug legalisation in Latin America.
A group of former presidents and influential social figures, including the Brazil's Henrique Cardoso, the Mexico's Ernesto Zedillo and Colombian ex-leader Cesar Gaviria, have called for the legalisation of marijuana.
But only last week Pope Francis criticised drug legalisation plans during a visit to Brazil.
Speaking at the inauguration of a clinic for drug addicts in Rio de Janeiro he said it was "necessary to tackle the problems which are at the root of drug abuse, promoting more justice, educating the youth with the values that live in society, standing by those who face hardship and giving them hope for the future".