By Shern-Min Chow / 11 News

Each year Americans spend hundreds of millions of dollars on prescription drugs in Mexico. But we’ve discovered that the decision to buy medications south of the border can be dangerous – and deadly.

They come by the busloads, seeking a magic pill. Leading the consumer charge into border town pharmacies are senior citizens.

“This one is for highblood pressure,” Nellie Pratt says as she shows off her medications. “This one is for shakiness. You know, tremors.”

Here in the United States, the prescription drug known as Inderal costs Pratt 31 cents a pill; in Mexico, the equivalent costs just 5 cents. Norvask costs $1.40 a pill in the U.S., but its Mexican counterpart sells for a mere 16 cents.

south of the border.

U.S. drugs are expensive partly because they are so stringently regulated. The FDA estimates 25% of the drugs made in Mexico's unregulated pharamceutical industry are counterfeit. So we decided to put Nelle's drugs and others-- to the test.

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Leading the consumer charge into border town pharmacies are senior citizens.

Forensic toxicologist Dr. Ernest Lykessa has tested prescription drugs from Mexico before and found, in some cases, “nothing but milk sugar, or talcum powder.” Before checking our stash of Mexican medications, he warned us that potency, purity or heavy metal contamination could be problems. Metals can leach into drugs, during cheaper manufacturing processes .

The Mexican version of Norvasc was 100% potent, but had significant levels of chromium. And that, Lykessa warns, is dangerous.

“Yes, yes it is,” he says. “The kidneys are going to be impacted.”

Nelle's Inderal was 95% potent.

“It’s possible the drug had passed its expiration date, yes, which is why it was cheaper,” Lykessa says.

Worse yet, it bore several heavy metal contaminants. The most frightening problem: 150 times the acceptable level of lead.

"It causes dementia,” Lykessa says.

Would he give that pill to his grandmother? "No,” he says. “I wouldn't give it to my dog."

Nelle was suprised. Besides cancer, those metals also contribute to neuromuscular problems – like trembling.

“I'll be darned,” she says. “Maybe that's why I was shaking so bad yesterday.”

But the medical equation gets even more complicated. Consider Celia Flores, a 37 year old mother with three children and a debilitating back condition that will eventually put her in a wheelchair.

“With no insurance it’s hard …” she says. “I did go without any medication for about a year.”

Then, she started buying her muscle relaxer, Diclofenac, in Mexico. The difference in cost is astonishing.

“For 3 months, I only spent 20 dollars,” she says. Here in the U.S., for the same supply of drugs, she says she would have paid $391.

She gave us her Diclofenac, along with some of a friend’s supply of Ranitidine, a stomach medicine sold here as Xantac.

The copycat Xantac looked bad from the start.

“They're falling apart,” Lykessa said as he tested the drugs.

The results? Celia's back medicine was 100% potent and 100% pure. But her friend’s counterfeit Xantac show a potency of only 72%, Lykessa says, “which makes it useless.”

But what the doctor found next so startled him, he repeated the test three times: chromium 800 times the acceptable level, arsenic 1500 times the acceptable level.

“You take this pill for stomach ulcer,” Lykessa says, “you end up with stomach cancer. You’re going to die. We’re talking death here.”

So we went back to Celia, first giving her the good news about her back medicine. Was she relieved?

“I never felt worried,” she says.

But as for her friend’s stomach pills, she was surprised.

The counterfeit Xantac results prompted Nelle to take action..

“I'll pass that along to my family,” she says, “because they all take it.”

So buying Mexican drugs may seem like a bargain, but sometimes saving a dollar can be a gamble.