The best thing to do would be to legalize and regulate cartel-related drugs. The cartels would not be able to compete if the war on drugs was ended, basically.
Not only would it have the effect of weakening the cartels, but it would also lead to a lot of harm reduction, because drug addicts would actually know what they are putting in their bodies.
A good example of this is Marijuana being legalized in most of the US, and its effect on the cartels. The cartels have almost completely backed out of the cannabis trade, because they can’t compete with the quality, price, and convenience of being able to buy weed legally at a store.