Cheese has been called “dairy crack,” compared with morphine and heroin, and accused of being addictive because it contains opioid compounds. There is a kernel of real science behind those claims, but the reality is far more interesting, and far less alarming, than the headlines might suggest.

It’s true: cheese really does contain opioid-active peptides called casomorphins, and our digestive system can produce more of them when it breaks down dairy protein. These compounds can interact with the same broad receptor system targeted by drugs such as morphine.

However, that doesn’t mean eating cheddar is comparable to taking an opioid drug. So, what are cheese opioids actually doing in your body? Can they make cheese addictive? And is there any reason to change the dairy you eat?

Does Cheese Really Contain Opioids?

Yes. Certain cheeses contain opioid peptides called beta-casomorphins. Casomorphins originate from casein, the major protein family in cheese. Within casein is beta-casein, a long chain of amino acids containing smaller peptide sequences. When enzymes cleave beta-casein, some of these sequences can be released as beta-casomorphins.

They are called opioid peptides because they can bind to and activate opioid receptors, particularly mu-opioid receptors. Casomorphins are not morphine: morphine is one specific opioid molecule, while casomorphins are protein fragments with opioid receptor binding activity.

Trace amounts of actual morphine have long been reported in milk, around 200-500 nanograms per litre in early research, but this is separate from the casomorphin story and represents an extremely small amount.

Casomorphins form in two places. Firstly, cheesemaking itself breaks down casein. Starter bacteria, fermentation and ripening can release BCMs, while other microbial enzymes can subsequently destroy them. This helps explain why concentrations vary greatly between cheeses. A recent study of 26 commercial U.S. cheddars, for example, detected BCM-7 only in cheeses made with A1-containing milk, whereas another opioid peptide, BCM-9, was present in both A1-containing and A2-only cheeses.

Secondly, digestion can release additional casomorphins from beta-casein after we eat dairy. Exactly how much of our total exposure comes from being preformed in cheese versus being generated during human digestion is still not well established.

What Do Cheese Opioids Do in the Body?

The word opioid immediately makes most of us think of the brain, pain relief and euphoria. But that isn’t necessarily where food-derived opioids have their most relevant effects.

Opioid receptors are also found throughout the gastrointestinal tract, where they help regulate intestinal movement and secretion. BCM-7 is a known mu-opioid receptor agonist, and research suggests it can directly influence gastrointestinal function.

Experimental research has linked casomorphins with changes in gut motility, intestinal transit and digestive secretions. Human studies comparing milk containing A1 beta-casein with A2-only milk have also reported greater digestive discomfort and slower gastrointestinal transit with the A1 milk. One crossover trial reported a roughly 6-hour increase in transit time, along with greater GI symptoms and inflammatory markers.

This matters because A1 beta-casein is particularly conducive to the release of BCM-7. But could BCM-7 also travel from the intestine into your bloodstream and eventually reach your brain? That part is much less clear. To exert a substantial central opioid effect, intact BCM-7 would need to survive digestion, cross the intestinal barrier, survive additional enzymes in the circulation and potentially cross the blood-brain barrier.

One important defence that possibility is dipeptidyl peptidase-4 (aka DPP-IV or DPP-4), an enzyme found in the intestinal brush border and elsewhere in the body. BCM-7 is susceptible to DPP-IV degradation, which may substantially limit how much intact peptide travels beyond the intestine.

This highlights an important distinction: showing that BCM-7 can activate an opioid receptor is not the same as showing that eating cheese delivers a morphine-like dose to your brain.

Casomorphins may also have non-opioid actions. An older human experiment found that BCM-7 could directly release histamine from isolated white blood cells and cause a histamine-like skin reaction when injected into the skin. However, whether this occurs to a clinically meaningful degree after simply eating dairy remains unknown.

Is Cheese Addictive?

This is where the science and the headlines really part company.

There is currently no convincing evidence that casomorphins make cheese addictive in humans.

Much of the “cheese is crack” story can be traced to a widely reported 2015 PLOS ONE study examining foods associated with addictive-like eating.

But the researchers did not test casomorphins, nor did they measure opioid receptors, dopamine responses to cheese, dependence or cheese withdrawal. Instead, participants reported which foods they found difficult to control. The strongest predictors were processing, fat content and glycemic load, with highly processed foods containing combinations of added fat and refined carbohydrates being particularly problematic. And cheese itself ranked only 16th out of 35 foods in the survey.

Pizza topped the list, but that doesn’t prove cheese was responsible. The study’s senior author, Ashley Gearhardt, later specifically rejected that interpretation, saying that cheese on its own was not particularly problematic.

There is also research that more directly tests whether casomorphins behave like rewarding drug: in a 1994 experiment on rats, researchers gave the animals relatively large injected doses of beta-casomorphin and compared them with morphine using conditioned place preference, a standard test of drug reward. Morphine worked: the rats developed a preference for the environment associated with it. Casomorphin did not.

A more recent 2024 experiment produced the opposite-looking result: planarian flatworms directly exposed to casomorphin displayed several behaviours interpreted as addiction-like. But the authors themselves acknowledge important limitations, including the dose, method of exposure and major differences between purified peptide exposure in flatworms and normal human digestion.

So cheese may certainly be craveable, rewarding and easy to overeat. Its combination of fat, salt, texture, aroma and flavour provides plenty of reasons for that without invoking drug addiction. But being highly pleasurable is not the same thing as being pharmacologically addictive.

Are Casomorphins Good or Bad for You?

The answer may be both, or neither, depending on the peptide, dose, and individual. BCM-7 has received the most scrutiny. Researchers have investigated possible links with gastrointestinal symptoms, inflammation, cardiovascular disease, type 1 diabetes, autism, and other neurological conditions.

But this is where the quality of evidence becomes crucial. A comprehensive 2026 review concluded that evidence connecting BCM-7 with conditions such as cardiovascular disease, type 1 diabetes, and autism remains questionable. Much of it comes from laboratory experiments, animal research, ecological associations or small human studies rather than robust clinical trials. Overall evidence quality was rated as low to moderate, with inconsistencies and a risk of bias.

The gastrointestinal story is more plausible because casomorphins can act locally without first reaching the brain. Human A1-versus-A2 milk trials also provide some evidence that beta-casein type can influence digestive symptoms. Still, most of this research has focused on milk rather than cheese, so we shouldn’t assume every finding applies directly to a serving of Gouda.

There is another side to the story, too: casein-derived peptides have demonstrated antioxidant, ACE-inhibitory, and immunomodulatory activities, although human evidence for these benefits remains limited. Different casomorphins may behave differently: BCM-9, for example, has been investigated for antioxidant and blood-pressure-related effects.

In other words, the evidence that casomorphins exist and are biologically active is strong. The evidence that eating them either causes disease or delivers major health benefits: not so much.

Should You Change the Dairy You Eat?

For most people, current evidence really doesn’t justify avoiding cheese or dairy simply because they contain or generate opioid peptides.

A1 and A2 beta-casein differ by just one amino acid, but that difference makes BCM-7 much easier to release from A1 beta-casein. For someone who experiences gastrointestinal symptoms with conventional milk, this may be yet another reason to experiment with the A2 variety.

Future research is likely to elucidate the significance of casomorphin metabolism in the body. For now, contrary to the sensational headlines of ‘dairy morphine,’ an undoubtedly interesting mechanism at play in one of humanity’s most bingeable foods simply does not equate to addictive potential, health benefits, or harms.