The troubling backstories of hidden weight-loss ingredients

Here’s what I learned about the backstories of some of these ingredients and a transparency reform that’s been pending in Congress for years.

The Fine Print

Since June, the U.S. Food and Drug Administration has issued seven public alerts about products promoted for weight loss that contained undisclosed pharmaceuticals or other dangerous ingredients. That’s more than the agency posted on its website during all of 2024 and 2025 combined.

The products were sold online and possibly in some retail stores. Here’s what the FDA’s tests found: 

• Lipofit Extreme 2.0 Fat Burner nighttime tablets contained undisclosed 2,4-Dinitrophenol (DNP), a potentially deadly substance that can damage the eyes, skin, bone marrow, nervous system and heart, raise a person’s body temperature to dangerously high levels, and cause cardiac arrest. The daytime tablets contained undisclosed fluoxetine, the active ingredient in FDA-approved drugs, including Prozac, used to treat depression, bulimia, and obsessive-compulsive disorder. It can cause suicidal thoughts, abnormal bleeding, and seizures.

• Detoxi Slim contained undisclosed sibutramine, which can significantly increase blood pressure and heart rate and have life-threatening interactions with other medications. The FDA also flagged the product for this hidden ingredient in 2019. 

• Esbelta Intense Loss contained undisclosed sibutramine, desmethyl sibutramine, benzyl sibutramine, and sildenafil, the active ingredient in Viagra, which can interact with other medications and cause dangerously low blood pressure.  

• ZUBB Dietary Supplement contained undisclosed sildenafil.

• Esbelta Chupapanza Flat Belly contained undisclosed phenolphthalein, which studies suggest could increase the risk of cancer.

• B. Magi contained undisclosed phenolphthalein, neriifolin, and thevetin B. In addition to the undisclosed compound with cancer risks, the other two chemicals are found in the yellow oleander plant and can cause severe neurologic, gastrointestinal, and cardiovascular effects. 

• DMagic Plus contained undisclosed neriifolin, thevetin B and diclofenac, a NSAID pain and inflammation reliever that can increase the risks of serious heart and gastrointestinal issues.

The FDA identified the problems with Detoxi Slim and ZUBB Dietary Supplement “during an examination of international mail shipments,” according to the agency’s alerts for those products.

It’s unclear what drew regulators’ attention to the other products and why the agency issued a flurry of alerts about weight-loss products this summer after only posting two notices in 2025 and four in 2024. The FDA did not answer Healthbeat’s questions. 

Jeff Ventura, spokesman for the Council for Responsible Nutrition, a trade association for makers of major dietary supplements, told Healthbeat the rise in FDA alerts doesn’t necessarily mean there’s been a sudden increase in the problem.

It’s possible the FDA has been conducting increased surveillance, testing or enforcement activity related to certain categories of products, he said. 

“Weight-loss products have historically been an attractive category for bad actors because consumers may be looking for dramatic or rapid results,” Ventura said. He said products that are spiked with undeclared ingredients should not be confused with legitimate dietary supplements.

The Backstory

Several chemicals the FDA recently found hidden in weight loss products have dangerous histories. 

Dinitrophenol: an industrial chemical turned into a notorious 1930s weight loss pill

Public health officials became aware of the dangers of dinitrophenol during World War I, after French workers exposed to the chemical while manufacturing explosives became ill with high fevers and profuse sweating and sometimes died, according to a history of the drug published by an FDA official back in 2007.

But at lower levels of exposure, the workers lost weight. 

During the 1930s, this potentially useful side effect attracted the attention of a Stanford University pharmacologist and later others who marketed the chemical as a remedy that would “safely melt one’s fat away.” 

Young women were targeted in marketing with promises the remedy “will bring you a figure men admire and women envy,” according to the history paper.

The drug’s use continued despite other scientists warning about “alarming functional changes” to a person’s liver and heart. As many as 2,500 Americans might have lost their eyesight because of “dinitrophenol cataracts.”

The chemical and the harm it caused contributed to the passage of the Food, Drug, and Cosmetic Act of 1938, which gave the FDA the power to prohibit its use. 

Yet over the decades, dinitrophenol, also called DNP, has continued to find its way into some weight-loss products. Sometimes its presence is declared and other times it is hidden.

Internet marketing and sales have made it easier for the dangerous chemical to reach consumers. And around the world, people have continued to die, including a 43-year-old U.S. man in 2024. 

The product the FDA warned about in June that contained DNP — Lipofit Extreme 2.0 Fat Burner — is currently being recalled by a Florida website. The Aug. 27 recall notice says Ana Salazar Modela Tu Cuerpo Inc. hasn’t received “any known reports of adverse events.”  The company didn’t respond to questions from Healthbeat.

Phenolphthalein — a top-selling laxative pulled off the market over cancer concerns

Phenolphthalein had been in formulations of the over-the-counter laxative Ex-Lax for nearly a century. But in 1997, the maker of Ex-Lax recalled its products containing phenolphthalein after the ingredient was linked to cancer in animal studies. Ex-Lax products were reformulated at that time. In 1999, the FDA issued a final rule classifying phenolphthalein as “not generally recognized as safe and effective.”

Sibutramine — a controversial diet drug linked to serious adverse events

In 2010, sibutramine — sold as the diet drug Meridia — was pulled off the market amid FDA concerns about heart attack and stroke risks. The FDA approved the drug in 1997, despite  safety objections from the agency's scientific advisors. The consumer group Public Citizen in 2002 petitioned for the drug to be removed from the market, citing its association with nearly 400 serious adverse events and 29 deaths since its approval.

Why It Matters

Consumers buying weight-loss products marketed as all-natural supplements trust that the ingredients listed on the package are what’s really in the pills. 

They have no way of knowing they are ingesting hidden pharmaceuticals or other compounds that can carry life-threatening risks.

Unlike drugs, products marketed as dietary supplements are considered a category of food and aren’t required to undergo FDA approval before they are sold. Supplement makers are responsible for making sure their products are safe and that the labels accurately list ingredients.  

The FDA does some monitoring and testing of products marketed as supplements and can take action if the agency determines the product is unsafe, adulterated with an undisclosed ingredient, or a substance considered an unapproved drug.

But the market is huge — as many as 100,000 different products — and the FDA’s resources are limited.

“FDA is unable to test and identify all products marketed as dietary supplements that have potentially harmful hidden ingredients,” the agency says in its recent weight-loss product alerts, which are part of a list of more than 200 public notifications going back to 2009. 

“This list covers only a small fraction of the contaminated products on the market,” the agency notes. 

What to Watch

One challenge for regulators is knowing what’s being sold. 

Earlier this year, U.S. Sen. Dick Durbin, D-Illinois, reintroduced legislation that would require dietary supplement manufacturers to provide the FDA and the public with information about their products’ names, ingredients, allergens, and function claims, along with an electronic copy of the label.

It’s the latest attempt since 2022 to make supplement registration mandatory. 

The legislation has support from multiple consumer groups but has run into opposition from several supplement industry groups.

Two major supplement industry groups are divided in their views. The Natural Products Association argues the proposal would divert resources from research and innovation. The Council for Responsible Nutrition supports it, saying greater visibility into legitimate companies and products could help the FDA identify companies operating outside the system. 

Durbin’s bill was referred in January to the Senate Committee on Health, Education, Labor, and Pensions. In April, U.S. Rep. Maxine Dexter, D-Ore. and a doctor, introduced similar legislation in the House, which is now in the Energy and Commerce Committee. 

Neither bill has advanced since being referred to committee. 

Reach me at [email protected] or through the messaging app Signal at alisonyoungreports.48. Read more about me and my work here. Forwarded this email? Sign up for free to receive this newsletter.

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