Last updated 26 August 2026 · Originally published 6 April 2020
Endocannabinoid deficiency is the theory that some hard-to-treat conditions — migraine, fibromyalgia and irritable bowel syndrome above all — happen because the body is not making enough of its own cannabinoids. If that were true, it would explain why cannabis helps some people with those conditions, and it would make CBD look like a way of topping up something you are short of. It is a reasonable idea with real evidence behind it, and the basic premise — that people differ in how much of this system they have — is very likely right. What is still open is what those differences do, and how to find out whether you have one.
Your body makes its own cannabinoids
This part is not a theory. Every human body produces compounds that act on the same receptors THC does. The two best known are anandamide, named after the Sanskrit word for bliss, and 2-AG. Together with the receptors they act on and the enzymes that make and break them down, they form the endocannabinoid system, discovered in the early 1990s when researchers went looking for why THC does what it does. It helps regulate pain, appetite, mood, sleep, memory and inflammation, which is a long list, and it is why cannabis affects so many things at once.
The runner’s high is probably the most familiar example of it working. For years it was credited to endorphins; endocannabinoid signalling, including anandamide, now appears to contribute substantially to it, and it is probably not simply an endorphin effect.
The theory
In 2004 the neurologist Ethan Russo asked whether the endocannabinoid system, like other biological signalling systems, might become underactive in some people. He suggested that a shortage of endocannabinoids, or receptors that do not respond to them properly, might underlie a group of conditions that share three features: they involve pain that the nervous system amplifies, they often occur together in the same people, and cannabis seems to help them. Migraine, fibromyalgia and IBS were his main candidates, with PTSD, motion sickness and some others as possibilities.
He called it clinical endocannabinoid deficiency and restated the case in 2016, arguing that the evidence had grown.
The premise is not far-fetched. People vary in every other biological system, and they vary in this one: the gene for the enzyme that breaks down anandamide comes in different versions, and people carrying one common variant have more anandamide and, on average, less anxiety. At the extreme, a Scottish woman described in 2019 was found to have a rare mutation that leaves her with very high anandamide. She feels almost no pain, no anxiety, and heals unusually fast. This shows that extreme variation in the endocannabinoid system can have striking effects. It does not show that the reverse pattern causes migraine, fibromyalgia or IBS.
What supports it
The strongest single piece of evidence is from migraine. A 2007 Italian study measured anandamide in the spinal fluid of people with chronic migraine and found it markedly lower than in people without. That is a direct measurement of the thing the theory predicts, in the place it predicts it. A 2013 PTSD study found lower anandamide alongside increased availability of the CB1 receptor, possibly a compensating response; a newer imaging study did not reproduce the receptor difference, so the PTSD evidence remains unsettled. And people with these conditions do report benefit from cannabis at rates that are hard to dismiss entirely, even though such reports cannot show why.
What the migraine trial does — and doesn’t — show
In a trial published in 2026, 92 people with migraine each treated separate attacks with four different vaporised preparations: THC-dominant, CBD-dominant, a THC-and-CBD mix, and a placebo. The mix beat placebo for pain relief and pain freedom at two hours, with benefit lasting into the next day. THC alone gave some relief. The CBD-only preparation was no better than placebo on any measure. It is the first proper trial of cannabis for acute migraine, and it is a real result.
Two things to keep separate. This is evidence that one THC-and-CBD preparation can treat an acute migraine attack. It is not evidence that the participants had an endocannabinoid deficiency or that the treatment corrected one; the trial did not measure endocannabinoids. And if you are reading about the theory because you are considering CBD, the finding to hold on to is that in the one condition with the best evidence for it, CBD by itself did not help, and the preparation that did contained THC. That is a finding about the plant, and it favours the plant. It does not favour the CBD aisle.
What complicates the theory
First, the measurements are thin and not always in the right direction. The migraine spinal-fluid finding is one study. In fibromyalgia, some studies have found endocannabinoid levels normal or even raised, which is the opposite of a deficiency. Nobody has shown that low endocannabinoids come before the condition rather than after it, or that raising them fixes it.
Second, there is no test. Endocannabinoids are measured in research labs from spinal fluid or blood, the results vary with time of day, diet, stress and exercise, and nobody has established what a “normal” level is, let alone a deficient one. No measurement can currently diagnose a deficiency; any clinic or website claiming otherwise is applying an interpretation that has not been validated.
What CBD actually does here
CBD is not an endocannabinoid and does not replace one. It barely touches the receptors that anandamide acts on. The theory of how it might help is that it slows the breakdown of anandamide, so more of your own stays around longer — a mechanism seen in the laboratory and in one small human study of schizophrenia, and disputed since. Even if it works that way, the doses in those studies were several hundred milligrams a day, well above a retail serving, and the migraine trial is a reminder that the mechanism did not translate into relief.
If the endocannabinoid system is the thing you want to act on, two things have better evidence than CBD. One is exercise, which raises your own anandamide and is free. The other, where it is legal, is THC, which acts on the receptors directly rather than nudging what your body makes — and in the migraine trial, THC-containing cannabis is what worked. That comes with THC’s own downsides, which are real, but it is the honest answer to the question the theory raises.
What to take from this
Endocannabinoid deficiency remains a plausible but unproven explanation. We know the system varies between people and is altered in some illnesses. We do not know whether a defined deficiency causes migraine, fibromyalgia or IBS, and there is no clinical test for one. The strongest direct signal is a small migraine study showing reduced anandamide; the fibromyalgia and IBS evidence is much weaker. The new migraine trial shows that THC-containing cannabis can help treat an attack. It does not prove the deficiency theory, and it gives no support to CBD alone. Our articles on migraine, pain and PTSD go through the trials condition by condition.
Nothing in this article is medical advice. Migraine, fibromyalgia and IBS all have treatments with proper evidence behind them; talk to a doctor before replacing any of them.
