"However, during fiscal years 2000-2005, the United States provided about $6.2 billion to support counternarcotics and related programs in the source and transit zones (see table 1).12 In the source zone, U.S. assistance supports eradication and interdiction efforts and related programs for alternative development and judicial reform, primarily in Bolivia, Colombia, and Peru. In the transit zone, the United States provided about $365 million in assistance—primarily to El Salvador, Guatemala, Haiti, and Mexico —to support interdiction and other law enforcement programs."
"For fiscal year 2006, the Administration has requested an additional $735 million for countries in the source zone and $77 million for countries in the transit zone."
"From fiscal year 2000 through 2005, the United States provided about $365 million in assistance to countries in the transit zone. Of this, Mexico received approximately $115 million to support its efforts to eradicate opium poppy and marijuana, and improve surveillance and intelligence capabilities."

Source

"Drug Control: Agencies Need to Plan for Likely Decline in Drug Interdiction Assets, and Develop Better Performance Measures for Transit Zone Operations," Government Accountability Office (Washington, DC: USGAO, Nov. 2005), GAO-06-200, pp. 10 and 23.
http://www.gao.gov/new.items/…