On the morning of June 1, 2011, Michael L. Sparling took the recommended dose of the workout booster Jack3d before doing a drill with his Army unit.

During the workout Sparling collapsed, and several hours later he died at a hospital of respiratory failure and cardiac arrest.

Sparling had purchased the Jack3d in a GNC store at Fort Bliss in El Paso. Despite a warning issued by the FDA in April 2012, the powder is still available in GNC stores across the country as well as online.

Now, Sparling's parents are suing GNC as well as USPlabs, the developer and marketer of Jack3d. The Sparlings are claiming that GNC and USPlabs misleadingly marketed Jack3d and did not warn consumers about its potential health risks.

A stimulant contained in Jack3d, dimethylamylamine (DMAA), has been linked to several deaths recently. In 2011, DMAA was identified in the toxicology reports of two soldiers’ deaths. It was also found in the body of Claire Squires, a British woman who died while running the London Marathon in 2012. Jack3d has since been banned in England.

Products containing DMAA, like Jack3d and OxyElite Pro, are commonly marketed as workout boosters. But in its warning letter last April, the FDA noted that firms that produce these supplements have failed to demonstrate the safety of their key ingredient, DMAA.

At the time of the letter, a spokesman for GNC said the company disagreed with the FDA's conclusion and was "unaware of any scientific or medical evidence which calls the safety of DMAA into question."

The lack of DMAA regulation troubles many in the medical profession.

"[DMAA] is a pharmaceutical-grade product which is being directly introduced into the supplement marketplace with absolutely no regulatory oversight," Dr. Pieter Cohen, an assistant professor of medicine at Harvard Medical School, told the New York Times.

Last month New York State Sen. Jeffrey Klein called for DMAA to be banned from all sports nutritional supplements in the state. Klein labeled DMAA as "possibly the most dangerous, lethal and unregulated performance-enhancing drug on retail shelves today."

"The FDA is still taking a wait-and-see approach, still looking at it, still investigating it. I think we have to act now," Klein told reporters in January. "We're putting young people and people who are interested in sports, people getting sort of a quick fix at risk each and every day."

Klein's concern with the FDA's inaction is not unique to him. Steve Mister, the chief executive of the Council for Responsible Nutrition, told the New York Times that the FDA needed to be more clear about how it views DMAA.

"It is incumbent upon the F.D.A. to make a decision as to whether it is a legitimate and safe dietary ingredient,"Mister said.

This is far from the first time USPlabs has gone to court to defend or protect its product. In December, it reached a $2 million settlement with consumers in California court while also agreeing to make warning statements larger and easier to understand.

In October, USPlabs sued the owner of a supplements store in Reno, Nev., who described Jack3d as an "amphetaminelike compound" that “speeds up your heart rate” and could "possibly" cause death. The lawsuit, which was filed in a federal court in Dallas, was dismissed for lack of jurisdiction.