More than 22,000 people have disappeared since the Mexican government launched its war against drug cartels in 2006 - leaving the victims' families in limbo.
The talks between Santos and Clegg will be seen as a significant strengthening of the emerging liberal alliance on drugs reform in the lead up to the 2016 UN Special Session on drugs.
Iran has long had one of the world’s biggest drug dependence problems, but the government’s attitude toward the drug war remains rife with contradiction.