Save your trip unless you will be satisfied with Tylenol 3 or valuim.
Sometimes you can get something stronger. I have gotten percodan once and another time I was offerred Oxy but it was $12.00 a pill. To much for me.
Mexican drugs have erratic qualities. Sometimes they work and sometimes they don't.
Lastly, forget about any great 'deals' on drugs. Mexico has a two price system-one for natives and one for gringos.
But if you must go, do go to one of the 'doctors' near the pharmacies. At least you can take the prescription though customs and while some pharmacies will sell without one of these prescriptions, they charge more-i.e. they usually double the price without the perscription. so play it safe if you go.
Tylenol 3 is better than nothing. But I would not journey a long distance to try Mexico.
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Paranoia is just hightened awareness.