Home > Safety First > Does Coke or Pepsi contain 4-MI – a cancer causing agent?

Does Coke or Pepsi contain 4-MI – a cancer causing agent?

Is a Coke or Pepsi or any kind of cola, for that matter, safe to drink?  Well, you should think twice before you give them to your children.  You should think again before you drink colas while you are pregnant if you are a woman.  Not only are there health concerns with colas using high fructose corn syrup, but colas may also contain a cancer-causing agent called 4-Methylimidazole (4-MI).

The state of California has been a leader in setting the standards for environmental and food safety concerns.  In January 2011, the Office of Environmental Health Hazard Assessment from the California Environmental Protection Agency added 4-methylimidazole CAS No. 822-36-6 as a carcinogen in Proposition 65 – it is also known as the Safe Drinking Water and Toxic Enforcement Act  that was ratified in 1986.  Proposition 65 basically provides guidance on the maximum allowable dosage levels for listed chemicals causing reproductive toxicity in humans.  Businesses are then required to provide a warning label if the listed chemicals go over the maximum allowable dose.

According to the report, the allowable consumption of 4-MI in one day is 29㎍.  If intake levels of 4-MI are greater than 29㎍, the food manufacturer must place a carcinogenic warning label on its product.

In the January 2008 issue of Archives of Toxicology an article entitled: Toxicity and Carcinogenicity Studies of 4-Methylimidazole in Rats and Mice, revealed that  4-Methylimidazole was found to be a carcinogen in mice.  In particular, the 4-MI chemical induces alveolar bronchiolar adenoma and carcinoma in both male and female mice.  It may also induce mononuclear cell leukemia in female rats.  Higher levels of 4-MI increased the risk of cancer in rats as well.

It is important to note that there are currently no studies linking 4-MI in humans to cancer.  Even so, it is generally accepted that if a specific chemical is a cancer-causing agent in animals, then it is carcinogenic to humans.

What kinds of food contain 4-MI?  An abundant source of 4-MI is found in caramel coloring.  Caramel coloring is used in foods ranging from oyster sauces to soft drinks.  A toxicology research team led by Professor Taka Shibamoto of Environmental Toxicology in UC Davis first discovered 4-MI in colas.  Of course, caramel coloring is most notably used in cola soft drinks.  This gives the cola its distinctive dark-brown coloring.

Why is there 4-MI in caramel coloring to begin with?  There are four main methods used to create caramel coloring.  Regarding those methods that use ammonium compounds, 4-MI is formed as a natural byproduct during the creation of caramel coloring.

In February 2011, the Center for Science in the Public Interest (CSPI) petitioned the FDA to ban this kind of caramel coloring.  It also wanted the cosmetic additive renamed “chemically modified caramel coloring” or “ammonia-sulfite process caramel coloring”.

Coca-Cola and Pepsi avoided the placement of warning labels mandated in Proposition 65 by reducing the levels of 4-MI in colas sold in California.  However this is not true for the rest of the United States and other parts of the world.  It is surprising that the standards for food additive regulations are different for the same product even among US states.  To be fair some cola companies have taken action domestically to reduce the levels of 4-MI, but as of yet, colas sold abroad have yet to see the light.

The U.S. Food and Drug Administration has stated that a person would have to drink over a 1000 cans of cola a day to obtain concentration levels of 4-MI  that caused cancer in mice.  In addition, it is to be reiterated that there are no studies linking 4-MI to cancer in humans.  And the  metabolic mechanism of 4-MI in humans is unknown and it may be totally different in humans versus animals.  Thus, 4-MI can prove to be harmless, but then again, it could be dangerous.

Humans are not mice and there have been many examples in drug development where there seemed to be no adverse effects in mice, but toxic effects were present in humans during drug-trial studies.  Because of this uncertainty, it is better to err on the side of caution and place an outright ban on caramel coloring that contains 4MI for the sake of public health.  But more importantly, if it is possible to create caramel coloring without the production of 4MI, why not use such methods for the entire batch of all colas immediately and not for only Californians?

Although colas have been the most visibly targeted products,  there are many sauces and food items that use of caramel coloring as well.  Therefore, consumers should encourage scrutiny of these foods and urge manufacturers of caramel coloring to create their products without 4-methylimidazole (4-MI).


1.  OEHHA Office of Environmental Health Hazard Assesment.  Proposition 65  http://oehha.ca.gov/prop65/background/p65plain.html

2.  Chan PC, Hills GD, Kissling GE, Nyska A.  Archives of Toxicology 2008 January. Toxicity and Carcinogenicity Studies of 4-Methylimidazole in Rats and Mice.

3.  Center for Science in the Public Interest.  2011 February 16.  FDA Urged to Prohibit Carcinogenic “Caramel Coloring”   http://www.cspinet.org/new/201102161.html

2.  Daily Mail.  As a cancer scare erupts over a chemical in the fizzy drink … just how safe is a can of Coke? http://www.dailymail.co.uk/health/article-2166193/Coca-Cola-cancer-chemical-scare-How-safe-Coke.html

3.  Consumer Report. August 10, 2012 http://www.kbs.co.kr/1tv/sisa/1004/

  1. July 8, 2013 at 5:32 pm

    The Center for Environmental Health (CEH) has recently published a press release in July 3, 2013 to update their investigation of 4-Methylimidazole (4-MI) in colas Coke and Pepsi. They found that Coke has changed the formula of its Caramel Coloring nationwide Outside of California but Pepsi is still using the coloring containing 4-Methylimidazole (4-MI) – a cancer causing agent.

    Due to proposition 65 in California, foods that contain 4-Methylimidazole (4-MI) must show a label that it is carcinogenic. Due to this action, Coke and Pepsi changed their caramel coloring formulation to avoid putting the carcinogenic label on their cola cans.

    In a study of 10 states outside of California, 9 out of 10 states have Coke products without 4-Methylimidazole (4-MI) but all of Pepsi products containing high levels of the cancer causing agent.

    While the levels of 4-Methylimidazole (4-MI) are actively being followed up and recognized in the U.S. other european countries including the UK and asian countries ie. South Korea has voiced their concerns over 4-Methylimidazole (4-MI).

    It is interesting to note that some vendors such as Costco are selling Coca-Cola made with Cane Sugar instead of High Fructose Corn Syrup. While this may be a good step, the Coca-Colas are made in Mexico where there is no regulation of the level of 4-Methylimidazole (4-MI) in food/ drinks. According to investigative reports from the Korean Broadcasting System, the level of 4-MI are in many instances higher in other countries vs. the U.S. Whether this currently applies to Mexico remains to be seen.

    Further investigation worldwide and active follow-up is needed.

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