By Fredrik Dahl VIENNA (Reuters) – Uruguay's legalization of marijuana violates an international drug control convention and fails to consider a negative health impact, a body set up to monitor compliance with the five-decade-old treaty said on Wednesday. The president of the International Narcotics Control Board (INCB), Raymond Yans, said the change would not protect young people but would rather have the "perverse effect of encouraging early experimentation" and lowering the age of first use. Adding weight to the criticism of Tuesday's move by Uruguay – the first country to take such a step – the U.N. anti-drugs office said it agreed with the INCB and that states should work closely together to deal with the global drugs challenge. "It is unfortunate that, at a time when the world is engaged in an ongoing discussion on the world drug problem, Uruguay has acted ahead of the special session of the U.N. General Assembly planned for 2016," David Dadge, spokesman for the U.N. Office on Drugs and Crime (UNODC), said.