preventing each other from creating effective policies against illegal drugs
"seeking assistance from international groups to stop the illegal drug trade"
This might be part of the Mexican international politics, but was never part of the American one. Even now. It's false.
"working together to stop the drug cartels and trafficking of illegal drugs"
Specially lately, with Trump, there's not much cooperation between the two countries and right before Trump, the USA wasn't that big on The war on drugs. So it's false.
"collaborating with leaders of the drug cartels to confine their activities"
This just seems very unlikely that either country would collaborate with criminals. It's false.
So by elimination we have:
"The United States and Mexico are preventing each other from creating effective policies against illegal drugs"
And considering that there's a lot of arguments and troubles going on because of Trump's foreign policy, disagreements between the two countries, the wall and so on; this is mostly likely the right answer.