More than 158 tons of drugs were seized at the U.S.-Mexico border this year in Southern California alone; most of it was marijuana.
And since 2008, a growing number of Mexican drug cartel leaders have also fallen.
Despite the progress, a government memo concludes that it has not slowed the flow of narcotics into the U.S.
Customs and Border Protection (CBP) spokesperson Michael Jimenez argued that this trend is a sign that the recent ramp up in border security is working.
"We know that we are having an effect on the drug smugglers and these criminal smuggling organizations," Jimenez said. "Because they are becoming more secretive in how they are bringing the narcotics in the vehicles."
According to CBP, the cartels have adapted to the increased security, and they are no longer able to bring in as many big shipments as before.
"Now we are becoming so good at detecting these narcotics, that they are putting things in smaller compartments," added Jimenez. "Smugglers have become very creative now in how they try to get these drugs past us."
But a recently leaked CBP memo contradicts the agency's main message.
By looking at drug seizures between 2009 and 2010, the memo found that despite the arrests of numerous members of criminal organizations in Mexico and the U.S., it did not "have a discernible impact on drug flows into the United States."
The total amount of drugs brought into the Southwest from Mexico, the memo concluded, is unknown.
