In a world of silly numbers, this is surely the silliest. First of all, the premise is absurd: the drug trade isn't going to disappear tomorrow. Industries don't just vanish without warning, and if they did, our estimates about their impact on the economy would likely be wrong. But most frustratingly, this claim is simply insane, like a story that a kindergartner would tell an amused parent: We saw a dog that was bigger than a school bus! The number of people working in the drug trade, which is to say, the Mexicans adding to the P in GDP via drugs, is less then 1 percent of the population, and less than 3 percent of the work force. Very high-end estimates of the drug trade's value place it at about 5 percent of Mexico's GDP. Even accounting for the indirect impact on the legitimate economy, the difference between 5 percent, which again is a high estimate, and 63 percent is quite significant. This is a junk stat that exists not to give government officials any insights about policy, but merely so writers can toss it into articles to raise eyebrows. Unfortunately, most of the people who read that stat will probably believe there's some truth to it.
Now, onto the origin of the stat. Evidently, it comes from a Cisen study earlier this decade. I've never seen the study (and I'd love to if anyone has a link), but assuming that it's legit, being from Cisen doesn't make it any less indefensible. Anyone with a modicum of common sense can safely declare sight unseen that its conclusion is ridiculous. (See above.) Oddly, I've never once seen the study referred to in the Mexican media, which, to be sure, is not hesitant about tossing outlandish stats into their articles. I believe it is mentioned by both Charles Bowden (in Down by the River) and Richard Grant (in God's Middle Finger, as well as in this piece), both of whom employ a very dark, narco-focused vision of Mexico in their writing. But a Spanish Google search for this study by a Mexican agency tuns up nothing.