Alison Young

USA TODAY

Nutritional supplement retailer GNC has stopped selling two products containing a new stimulant ingredient that is under fire from scientists, senators and a major industry group.

The products Redline White Heat and OxyTHERM Pro were being sold on GNC's website this week. But as of Wednesday afternoon, in the wake of a USA TODAY article, they had been removed from the online store. GNC web pages that had offered the products for sale have had all information stripped from them.

GNC officials would not answer questions about when and why they stopped selling the two products, which contain a chemical marketed under a variety of names including AMP Citrate, DMBA and 4-amino-2-methylpentane citrate.

"GNC does not typically comment on product selection or availability," GNC spokeswoman Laura Brophy said in an email late Wednesday.

The Vitamin Shoppe, as of Thursday also was no longer selling Redline White Heat on its website, which had offered it for sale as recently as Monday. A Vitamin Shoppe spokeswoman was not immediately available for comment.

On Wednesday morning, USA TODAY reported that two U.S. senators, a major dietary supplement industry group and a team of scientists were calling on the U.S. Food and Drug Administration to take regulatory action against products containing the ingredient. The compound is a chemical cousin to DMAA, a stimulant the FDA has warned is an illegal supplement ingredient that carries serious health risks, including heart attacks. The new compound, DMBA, is found in a wide range of supplements that continue to be sold by Amazon and other retailers as workout, weight-loss and mental focus products.

While GNC had no comment Wednesday, on Tuesday the supplement seller issued a statement to USA TODAY defending sales of the two products, saying in part: "Like all retailers, GNC relies upon the contractual representations and warranties made by the manufacturer of the product regarding its legality and safety. GNC is not aware of any regulatory commentary about, or actions against, these products or the ingredients they contain."

Pieter Cohen of Harvard Medical School, a co-author of a study published Wednesday analyzing the amount of the new stimulant in the two products and several others, said the FDA should hold both manufacturers and retailers responsible. "The question remains," Cohen said Wednesday, "Why did GNC not question the quality and safety of the supplements before they sold them?"

Officials with VPX Sports, which markets Redline White Heat, and PNI/deNOVOLABS, which markets OxyTHERM Pro, did not respond to requests for comment.

Read more articles in USA TODAY's Supplement Shell Game series, which investigates dietary supplements and their makers, at supplements.usatoday.com

Follow USA TODAY investigative reporter Alison Young on Twitter: @alisonannyoung