Mexican Jails are not fun.
I spent aprox 1 hour in one in the 70's for hitting a boulder in the Ensenada-Tijuana highway. (of course, I'd consumed enourmous quantities of beer prior to the incident)
I was able to pay "The Fine" on the spot with a hundred dollar bill I had hidden in one of my socks. (lifelong habit, when trveling to other countries)

Every so often Bush/Fox need a scapegoat/example on the "war on drugs/smuggling". It could be you. You don't want this. You really don't.
Besides, Mexican Pharmacies are famous for selling you what you want, then making a quick phone call to the federales
to report you. Keeps them off the [censored] list.