Last week a consumer advocacy group reported that the leading brown sodas contain levels of 4-methylimidazole (4-MI) – an animal carcinogen – high enough to cause cancer in 7 out of 1 million Americans. Days later, soda companies, including Coca-Cola and Pepsi, announced that they were reducing the amount of 4-MI in their colas to meet the limit set by California – the only state that regulates the substance.


However industry says it did not make this change for public health reasons, since the amount of 4-MI in colas does not actually pose a risk to consumers. Instead, companies want to avoid having to put a cancer warning label on cans in the event that government regulators decide to restrict 4-MI. 

But this change in policy, requested by the Center for Science in the Public Interest (CSPI) seems unlikely to come about anytime soon, as even the Food and Drug Administration (FDA) refuted the group’s claims that the 138 micrograms it found in brown sodas on average poses a cancer risk. 

“A person would have to drink more than a thousand cans of soda in a day to match the doses administered in studies that showed links to cancer in rodents,” said FDA spokesperson Doug Karas in a now widely-cited statement. 

According to Dr. James Coughlin, a toxicologist who studies animal carcinogen, the risk posed by 4-MI is even smaller than this government estimate suggests. 

The limit on 4-MI now being adopted by cola companies nationwide was set by California’s Proposition 65, which lists all chemicals considered carcinogens by the state. 

To set this threshold, rulemakers relied on the results of a 2007 study from the National Toxicology Program which found that 4-MI at high doses caused lung cancer in mice.


But in order for humans to reach the equivalent of even the lowest cancer-causing dose in mice, says Coughlin, a woman would have to drink 37,000 cans (12 oz) a day for the rest of her life. A man, on the other hand, would have to drink a whopping 95,000 cans a day during his lifetime. These figures are taken from a slightly more conservative study of colas done last year that found an average of 130 micrograms of 4-MI per can as opposed to the 138 micrograms found by CSPI. 

“It’s certainly not a health risk,” Coughlin told Food Safety News. “Cola is not causing cancer in humans. It’s just not happening.” 

In fact, he says, in the same study, rats were also given high doses of 4-MI, and none of them developed tumors. The chemical even reduced their risk of 5 other types of cancer (besides the lung cancer it produced in mice).

“I believe this is much ado about nothing,” he says. 

But Michael Jacobson, executive director of CSPI, says the organization is sticking by its petition to limit 4-MI nationwide. FDA’s claim that one would need to drink over 1,000 cans a day to risk cancer is “a ridiculous statement,” he says, “and it deserves ridicule.” 

“It’s disappointing to see FDA defending a cancer-causing chemical in the food supply,” he said in an interview with Food Safety News.

Jacobson says it’s not the dose but the percentage of mice that got tumors in the study that matters.  Since about 30 percent of the mice developed cancer, and a can of soda has about 1/1,000 of the amount of 4-MI administered to the mice, that would equate to 30 cancer cases in every 100,000 people. 

Coughlin, on the other hand, says you can’t apply the number of illnesses in an animal study directly to humans. 

“CSPI took these animal numbers and calculated cases of human cancer, but you can’t just take those animal statistics and transfer them,” he says. 

For this reason, adding 4-MI to California’s list of toxins was a mistake in the first place, he says, as it was based on the prevalence of cancer in mice and not adjusted properly for the human body.

“There is strong scientific evidence that the chemical never should have been listed by Prop-65.”

Nonetheless, Coke and Pepsi – whose products had the most 4-MI in CSPI’s study – are changing how they produce caramel coloring (this process is what creates 4-MI) in order to avoid backlash should nationwide policy adapt to California law.


“The companies that make caramel coloring for our members’ soft drinks are now producing it to meet California’s new standard, and it will be used in products nationwide,” said the American Beverage Association in a statement. “Consumers will notice no difference in our products and have no reason at all for any health concerns, as supported by FDA and regulatory agencies around the world.”

Editor’s note: An earlier version of this article quoted James Coughlin as saying “I believe this is much ado about something,” when in fact he said “I believe this is much ado about nothing.” The story has been updated to reflect this correction. 

  • Scott Bledsoe

    It is a shame that the FDA is standing up for these food companies that put these chemicals in our food. They do not have to use these things in the food products yet they continue to do so. Besides, no one no where has done any kind of study of the long term exposure to these things like over 20 – 30 years. How can someone say they are safe?

  • Dr Mitchel Eisenstein

    Those folks at coca cola put the source of color as caramel, browned sugar, not cancer causing chemicals. I want to those scientists for being liars, scammers, and potential murderers. These executives should be fed the concentrated chemical.

  • Alma

    I can’t believe people think it’s okay to have even small traces of carcinogens in our food. Do people forget that we eat MANY foods with these so-called small traces for carcinogens because the government says it’s ok to ALLOW such a small amount in a certain food?? Wake up folks. “Everything in modesty” goes out the door!
    Foods are chemicals and the human body was created/evolved to be sustained by certain ones and the other chemicals are POISONS to our bodies. We HAVE to stop allowing toxic products to gain approval to be sold to the public just because someone greases someone else’s hand.
    Obesity, Diabetes, and other degenerative diseases alone, are killing people more than ALL the wars and terrorist acts in ALL the history of mankind and most people don’t know or don’t care. It just amazes me…
    Please don’t count on the “experts” on this, people. Educate yourselves. You’ll find that 97% of all illnesses can prevented/cured by the right food alone. The kicker is that too many people would be out of work if we became healthy….

  • Michael Bulger

    I understand that Dr. Coughlin was talking about 4-MI, but when I read, “Cola is not causing cancer in humans,” I had to shake my head.
    Sugar-sweetened beverages are an empty source of liquid sugar that generally do not cause the reduction in calories from another source. Studies link drinking cola to obesity and type 2 diabetes. Obesity has been associated with cancer.
    It is old news that cola Coca-Cola is not good for you, but I thought it was worth pointing out.
    The CDC offers a Guide to Strategies for Reducing the Consumption of Sugar-Sweetened Beverages.

  • Emanuel

    Why the distracting off-topic comment about diabetes? You have entirely missed the point of the article Michael. Carcinogenicity of a brown coloring agent has been evaluated and found to be insignificant in real life settings. Perhaps when real scientists get around to evaluating your tenuous stretched string of causation: “cola > sugar > type II diabetes > obesity > cancer” your remarks will be pertinent unless, as is likely, no such relationship of tortured complexity exists in real life settings. Until then, no doubt you silly NYU operatives will continue to posture and cherrypick your way to pop science fame and fortune.

  • Dr. Wolffman

    If you are concerned about 4-MI you should really be concerned about DHMO it appears to be much more prevalent than 4-MI.

  • Steve

    “All things are poison, and nothing is without poison; only the dose permits something not to be poisonous.”
    Paracelsus knew more about toxicology in the 1500’s than most people alive today.

  • Michael Bulger

    Thanks for once again keeping us on topic, Doc Mudd. Your linear equation is flawed, though. For the sake of accuracy, we should say that real scientists in well-respected peer-reviewed journals tell us:
    Sugar-sweetened beverages (i.e., cola) = sugar -> obesity -> cancer risk (mortality & morbidity)
    Sugar-sweetened beverages (i.e., cola) = sugar -> type 2 diabetes (mortality & morbidity).
    (See link in previous comment and related articles.)
    However, you probably prefer the American Beverage Association’s line of thinking (Cola = $ = fun), or their marketing pitch (Cola = fun).
    I understood the point of the article, but found one quote in the article remarkable. The article was about cancer and 4-MI. It was not about the association between obesity and cancer.

  • Rick

    It’s a given in this powerful corporation-run plutocracy that as consumers we all have $$$ targets pinned onto our backs. We need complete transparency, labeling and independent analysis of all levels of production saying exactly of what is on and in our food supply.
    There’s no such thing as a “little” carcinogen. They add up and potentize. In Everyday Real Life Settings numerous brand name foods and household products are laced with synergistic MULTIPLE toxins to make them appear salable, attractive and to extend their shelf life — all adding to our Body Burden of toxic industrial chemicals, as well as excessive sugar and salt…
    But we can be our Doc and don’t have to buy it — when you see an ad for Pep-SI and their ilk — just think: Pep-NO!!

  • amused spectator

    The results are in: Cola is not causing cancer. All this agitated denial of perfectly valid scientific findings by people who probably don’t drink cola anyway. Don’t flatter yourselves into thinking your selfless fearmongering is protecting me. Also do not delude yourselves into thinking your angry subversive muckraking is influencing me toward your anarchic agendas. I only wonder how so many can so utterly and foolishly waste so much time and energy on things so unimportant. Like the guy who thinks we should turn the clock back to the 1500’s (Life expectancy back then was about 35 years, or so. He would probably be a ragged serf laid low by the plague, treating himself with tinctured nanny berries. What a genius!) After a hearty laugh at your expense I forget all about your silly hypochondria until your next round of panicked outcries. Pretty sure you won’t keep me waiting long.

  • One of my favorite movies is “Dr Strangelove” in which a demented right wing General Jack D Ripper rails against fluoridation and the poisoning of our “precious bodily fluids”. Everyone laughed at the time; now Ripper would be posting on this blog about “chemicals” in our food and the really funny part is he could have written most of the comments above.

  • Arnie Blunt

    Wow, 95,000 cans of soda a day for the rest of a man’s life to achieve the test dosage. 37,000 cans daily for a woman. Let’s have some volunteers from among the scaremongers to demonstrate that experiment. I reckon they will piss themselves to death long before cancer can develop. But maybe as a side effect it will make them temporarily smarter — it’s a good chance because they certainly couldn’t get any dumber. Seriously, some of them should consider this because the nickle deposit on the cans adds up at a lot more than they are being paid now as freelance propagandists for CSPI, NYU and NOFA.