LAS VEGAS — The nutritional supplement industry is one of the fastest growing and most lucrative in the United States. A Forbes article from 2013 predicts nutritional supplements will be a $60 billion industry by 2021.

But are nutrition stores prioritizing profit over public health and safety?

It's no secret that lots of people are looking for the magic pill that will transform their physique.

"Especially in Vegas," said a personal trainer in Nevada. "We say sex sells — having that particular look."

And claims like this certainly sound like magic: "helps with energy levels, anxiety, helps with inflammation — so recovery," the trainer said.

But there is no magic in a bottle. Especially some that are sold at nutrition stores across the country.

"I noticed on the back of the bottle it said 'Not for human consumption.' And that gave me a red flag," said the trainer.

He counts on the fitness industry for his livelihood and feared retaliation, so he asked us to conceal his identity. But he felt compelled to come forward after a client showed him a product she said Vegas Discount Nutrition employees advised her to buy: a pricey product with that ominous warning on its label.

"And I couldn't really recognize the brand, recognize the ingredients," the trainer said.

"Why would anybody — Vegas Discount Nutrition or anybody — sell a product to humans that's labeled 'Not for human consumption?' " KTNV asked Eduardo Lomeli, the vice president of finance for Vegas Discount Nutrition.

"It starts with tons of customer requests," Lomeli explained. "And we were allowing different locations to purchase based on requests. So it did come into a couple of our locations. I did not know... we did not know at the corporate level that it actually said 'Not for human consumption.' "

But their employees did.

A KTNV producer with a hidden camera went to several Vegas Discount Nutrition stores. At one location, the producer said to an employee, "It says 'For research use only. Not for human consumption.' But isn't it a pill that I'm supposed to take?"

"Well, that you're supposed to give to your lab rat," the employee answered.

"I'm pretty sure it was a joke," Lomeli said.

But does that make a certain product label a joke too? A product called "Brain Stem Research" that is available at one of their stories bears a label that says, "These specific scientific ingredients can help stimulate the lab rat brain like no other formula."

It contains instructions on how to take it — if you're a lab rat. The label says, "Lab rat use" before the instructions and says to check with a doctor before using it.

But rats aren't shopping for supplements. People like the concerned trainer's client are.

"Maybe it's a big money-maker," the trainer said. "Maybe they're using it to make money and they're not caring about the customer."

At $50-$80 a bottle for a one-month supply, certain products are a big money-maker. They're called selective androgen receptor modulators, or SARMs.

SARMs are not FDA-approved and the feds warn about "Unscrupulous companies who sell the potentially dangerous products" that are associated with increased risk of heart attack, stroke, life-threatening liver damage and other serious side effects."

An October study published in the Journal of the American Medical Association shows dietary supplements are flooded with unapproved drug ingredients not listed on the labels.

"That stuff's not good for you so we're definitely fixing that," Lomeli said about the SARMs found at Vegas Discount Nutrition.

The trainer we spoke to says his client got a different story from an employee who "Told her that it was natural, fine to take, no side effects."

KTNV wanted to see what employees would tell us. Here's more from the hidden camera shopping trip.

Producer: It looks like you're out of a lot of them.