The Plant Rx

Your resource for a plant-based diet

Cheese as an opioid? and, what the heck are “casomorphins”?

Posted by Jenn on March 15, 2011

If you talk to anyone who has recently switched to a plant-based diet and you ask them what food(s) they miss most, 9 times out of

Bovine Beta-Casomorphin-7 courtesy of Wikipedia

10, they will say cheese! Nope, not chocolate cake or BBQ, it’s cheese.  The same thing is the case if you talk to a vegetarian about completely transitioning to a plant-based diet and omitting dairy from their diet.  The typical response is, ” I would, but I can’t give up cheese”.

So, why is this?  After all, cheese does kind-of smell like dirty socks!

The answer is: Casomorphins.

Ok, well, that’s great – but, 1. What exactly are casomorphins and 2. How do they explain our love obsession with cheese? And, 3. does it even matter?

  • 1.  What are “Casomorphins“?

Definition: Casomorphins are peptides, i.e., protein fragments, derived from the digestion of milk protein.

Casein, is the milk protein that makes up 80-86% of the protein content of cow’s milk.  Casein has been documented to break down in the stomach to produce the peptide, casomorphin, an opioid that acts as a histamine releaser. [1]  (Although, not the topic of this blog post, the fact that casomorphins are a direct histamine releaser in humans is why so many people are allergic to dairy products; An estimated 70% of the population worldwide.)

Thus, the distinguishing characteristic of casomorphins is that they have an opioid effect.

  • 2.  How do casomorphins explain our love obsession with cheese?Unknown

In his book Breaking the Food Seduction, Dr. Neal Barnard discusses the addictive qualities of casein. He uses the example of chocolate to explain how this works:

University of Michigan researchers showed that chocolate does not merely tickle your taste buds; it actually works inside your brain in much the same way opiate drugs do. The researchers gave 26 volunteers a drug called naloxone, an opiate-blocker used in emergency rooms to stop heroin, morphine, and other narcotics from affecting the brain. It turned out that naloxone blocked much of chocolate’s appeal. When they offered volunteers a tray filled with Snicker’s bars, M & M’s, chocolate chip cookies, and Oreos, chocolate was not much more exciting than a crust of dry bread.

In other words, chocolate’s attraction does not come simply from its creamy texture or deep brown color. It appears to stimulate the same part of the brain that morphine acts on. For all intents and purposes, it is a drug-not necessarily a bad one and not a terribly strong one, but strong enough nonetheless to keep us coming back for more.

As common as chocolate addiction may be, it is by no means the only potentially addictive food, nor is it the most dangerous. In PCRM‘s research studies, when we take people off meat, dairy products, and other unhealthy fare, we often find that the desire for cheese, in particular, lingers on much more strongly than for other foods. While they might like ice cream or yogurt, they describe their feelings for cheese as a deep-seated craving. Could cheese really be addictive?

Well, in 1981, Eli Hazum and his colleagues at Wellcome Research Laboratories in Research Triangle Park, N.C., reported a remarkable discovery. Analyzing samples of cow’s milk, they found traces of a chemical that looked very much like morphine. They put it to one chemical test after another. And, finally, they arrived at the conclusion that, in fact, it is morphine. There is not a lot of it and not every sample had detectable levels. But there is indeed some morphine in both cow’s milk and human milk.

Morphine, of course, is an opiate and is highly addictive. So how did it get into milk? At first, the researchers theorized that it must have come from the cows’ diets. After all, morphine used in hospitals comes from poppies and is also produced naturally by a few other plants that the cows might have been eating. But it turns out that cows actually produce it within their bodies, just as poppies do. Traces of morphine, along with codeine and other opiates, are apparently produced in cows’ livers and can end up in their milk.

But that was only the beginning, as other researchers soon found. Cow’s milk-or the milk of any other species, for that matter-contains a protein, called casein, that breaks apart during digestion to release a whole host of opiates, called casomorphins. A cup of cow’s milk contains about six grams of casein. Skim milk contains a bit more, and casein is concentrated in the production of cheese…

{It takes approximately 10lbs of milk to make 1lb of cheese.  As milk is turned into cheese, most of its water is removed leaving behind concentrated casein and fat.  Thus, concentrated dairy products, like cheese, have especially high levels of opiates}

…When you drink a glass of milk or eat a slice of cheese, stomach acid and intestinal bacteria snip the casein molecular chains into casomorphins of various lengths. One of them, a short string made up of just five amino acids, has about one-tenth the pain-killing potency of morphine”.

At this point you might be wondering what the evolutionary basis might be for these opiates to be in a mammal’s milk.  Dr. Barnard, goes on to explain that:

“It appears that the opiates from mother’s milk produce a calming effect on the infant and, in fact, may be responsible for a good measure of the mother-infant bond. No, it’s not all lullabies and cooing. Psychological bonds always have a physical underpinning. Like it or not, mother’s milk has a drug-like effect on the baby’s brain that ensures that the baby will bond with Mom and continue to nurse and get the nutrients all babies need. Like heroin or codeine, casomorphins slow intestinal movements and have a decided antidiarrheal effect. The opiate effect may be why adults often find that cheese can be constipating, just as opiate painkillers are”.

  • 3.  Does all of this matter?

2. Review of the potential health impact of β-casomorphins and related peptides European Food Safety Agency, Scientific Report (2009) 231, 1-107


6 Responses to “Cheese as an opioid? and, what the heck are “casomorphins”?”

  1. […] The opioid “drug-like” effect of cheese [via […]

  2. DizzyJ said

    Why is the answer a resounding yes? Food has stuff that’s good for you and stuff, that if abused, is bad for you. Plants are nit defenseless lifeforms, just sitting around to joyfully fill our tummies. They have developed a vast array of ways to ensure propagation and to fend off predators.

    So cows produce minute levels of opiates (hmm, sounds kind of like a plant people don’t seem to rally against in it’s raw form). Excessive consumption of dairy might be bad, but not because of the optiates, any more than eating tooany vegan poppy bagels is bad for you because of the opiates they contain.

    This was a fascinating article, but the conclusion is a resounding overreach. I’d you want to make the case cheese is dreadful for ones health, make that argument. As somebody who believes that eating a plant-intensive diet is the healthiest option, this kind of overreach annoys me. It only serves to congratulate the converted, while making those who might consider dietary changes skeptical of any other claims being made.

  3. Jenn said


    Thank you for sharing your thoughts and opinion. I appreciate what your are saying, although, I do think you missed the point of the article. This topic of this article is to explain WHY we love cheese so much not about the fact that it is bad for you. I am not trying to make the argument that “cheese is dreadful for ones health” in this particular article.

    While, I do believe that, that was not the goal nor intention here.

  4. […] Ok, back to the opioid effect. It takes 10lbs of milk to make 1 lb of cheese. As milk is turned into cheese, most of its water is removed leaving behind concentrated casein and fat. So, concentrated dairy products, like cheese, have especially high levels of opiates, even morphine. […]

  5. Rhonda said

    Hello Dr. T,

    Fascinating subject. I recently had done some research on what makes cheese so addictive, and that is where I found out about Casomorphin in cheese. This is really important research to continue because I believe once people know what causes them to crave an animal product so strongly, they can refer to the science about what they are consuming and this may well make the connection for many.

    Like you, people that I talk to about a plant-based diet always respond with “I could not do without eating cheese.” So I just had to dig deep to find out why. I am thankful to know that there really is an answer to this question as it sure does make sense that the way we are designed is to attract our own babies and in the case of cows, their baby calves. Furthermore, consuming a high saturated fat such as meat and dairy only goes to confirm why we are seeing such an epidemic of obesity and disease in this country.

    Thank you for sharing your work,

    Kind regards,


  6. […] more about casomorphine addiction here while you enjoy a little bit of another kind of addiction – health in the […]

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