Following calls for action from scientists and consumer health advocates, the FDA has sent warning letters to a handful of diet supplement makers demanding that they cease selling products that contain a speed-like ingredient.

In 2013, FDA testing of diet supplements found that 43% of herbal supplements purporting to use the plant Acacia rigidula actually contained beta-Methylphenethylamine (BMPEA) — a chemical that has similarities to amphetamine, has never been tested for human safety, and which does not naturally occur in the plants used for these supplements.

A more recent study in the journal Drug Testing and Analysis confirmed the presence of BMPEA in these supplements even after the FDA’s initial tests.

The study notes that BMPEA was synthesized in the 1930s as a potential replacement for amphetamine, but that the chemical was never subsequently tested for human safety or efficacy, nor was it ever introduced as a pharmaceutical. And yet if users of these supplements take the maximum daily dosage, they could be “exposed to pharmacological dosages of an amphetamine isomer that lacks evidence of safety in humans.”

“The FDA should immediately warn consumers about BMPEA and take aggressive enforcement action to eliminate BMPEA in dietary supplements,” concluded the researchers.

And this week, the FDA did get around to throwing down the gauntlet over the BMPEA issue.

The Federal Food, Drug, and Cosmetic Act [FFDCA] limits “dietary ingredients” found in supplements to vitamins; minerals; herbs or other botanicals; amino acids; concentrates, metabolites, constituents, extracts, or combinations of any of these; and dietary substances “for use by man to supplement the diet by increasing the total dietary intake.”

Since BMPEA does not fall under any of these categories and its safety is undetermined, declaring it as a dietary ingredient on the product’s label would violate the FFDCA’s prohibition against false and misleading labels.

“Failure to immediately cease distribution [of the offending products] and any other products you market that contain BMPEA, could result in enforcement action by FDA without further notice,” read the letters. The law gives the FDA the authority to seize products that violate the rules and to enjoin the manufacturers from continuing to make and sell them.

The only argument the supplement makers could try to use is to claim that BPMEA is generally recognized as safe in food products. But since the FDA has no research showing this, the supplement companies would need to provide evidence of the chemical’s safety.

In total, the FDA has sent out five warning letters that cover eight different supplements: Fastin-XR (extended release); Fastin-RR (rapid release); Lipodrene (Ephedra Free); Conquer (Fruit Punch Slam & Raspberry Lemonade flavors); Critical FX; Sudden Impact; Phoenix Extreme; and Core Burner.

The makers of these supplements have 15 days to let the FDA know what they are doing to comply with the law.

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