Cracking down on dietary supplements containing a substance popularly known as DMAA, the U.S. Food and Drug Administration on Friday issued warning letters to 10 distributors and manufacturers, citing the companies for marketing the products without submitting evidence of their safety to the agency.

DMAA is dimethylamylamine, aka 1,3-dimethylamylamine, geranium extract, or methylhexanamine. It is frequently described as a so-called natural stimulant, the FDA said.

Before marketing products containing DMAA, manufacturers and distributors have a responsibility under the law [i.e., the Dietary Supplement Health and Education Act of 1994] to provide evidence of the safety of their products. They haven't done that, and that makes the products adulterated, said Daniel Fabricant, director of the FDA's Dietary Supplement Program.

The FDA warning letters advised the companies the agency is unaware of either evidence or history of use that indicates DMAA is safe.

The warning letters noted that DMAA is known to constrict blood vessels, which can elevate blood pressure and may lead to cardiovascular events ranging from shortness of breath to tightening in the chest to heart attack.

The FDA has received 42 adverse-event reports on products containing DMAA. Although these reports do not establish that DMAA was the cause of the events, some of these incidents were associated with cardiac disorders, nervous-system disorders, psychiatric disorders, and death.

To put the relevant corner of the U.S. dietary-supplement market in perspective, Americans spent an estimated $14.8 billion on so-called nonvitamin, nonmineral, natural products in 2007, according to National Health Statistics Reports No. 18 of July 30, 2009.

Signed by Michael W. Roosevelt, acting director of the Office of Compliance in the Center for Food Safety and Applied Nutrition at the FDA, the warning letters were sent to the following companies (whose affected products appear in parentheses):

--  Exclusive Supplements (Biorhythm SSIN Juice).

--  Fahrenheit Nutrition (Lean Efx).

--  Gaspari Nutrition (Spirodex).

--  iSatori Global Technologies LLC (PWR).

--  Muscle Warfare Inc. (Napalm).

--  MuscleMeds Performance Technologies (Code Red).

--  Nutrex Research (Hemo Rage Black, Lipo-6 Black Ultra Concentrate, Lipo-6 Black, Lipo-6 Black Hers Ultra Concentrate, Lipo-6 Black Hers).

--  SEI Pharmaceuticals (MethylHex 4,2).

--  SNI LLC (Nitric Blast).

--  USP Labs LLC (Oxy Elite Pro, Jack3D).

Each of the companies has 15 business days to respond to the FDA with concrete steps it will take to address the issues raised in the warning letters.

Based on their online presence, all of the companies appear to be privately held, and most of their affected products seem to be mainly marketed to people interested in muscle-building.

Update, April 30, 2012, 4:45 p.m. EDT

Contrary to the appearance of the iSatori Technologies Inc. online site, the Golden, Colo.-based company began to be publicly traded on the OTC Bulletin Board under the ticker symbol IZZI this month, following the completion of a merger with Integrated Security Systems Inc., according to a Business Wire release.

In response to its FDA warning letter, iSatori announced in a PRWeb release that DMAA will soon be a moot issue for the company, noting: Four months prior to receiving this letter, ... the company had made a business decision to reformulate its PWR [product] to remove DMAA for marketing and distribution reasons, and steps toward manufacturing and labeling of the reformulated products already have been under way. ISatori therefore intends to continue its plans to reformulate its PWR product to remove DMAA and to have the new product on the market on and after June 30 ...

ISatori also discussed the PWR product's financial contribution to the company last year, saying, For the year ended December 31, 2011, iSatori sales of the affected product, PWR, constituted approximately $330,000 of revenues, contributing less than $178,000 of gross profit to the firm.