How It Works

To understand why cannabis can help with some medical problems, and why it's useless or risky for others, it helps to know what it actually does inside the body. The short version: your body runs a signalling network called the endocannabinoid system, and the compounds in cannabis plug into it. The plant didn't evolve to treat human illness. It just happens to make molecules shaped like the ones we already use ourselves.

The endocannabinoid system, briefly

The endocannabinoid system (ECS) is a network of receptors found throughout the brain, nervous system and immune system. Your body makes its own cannabinoids, anandamide and 2-AG, that act on it to help regulate everyday things like mood, appetite, sleep, pain signalling and immune response. Think of it as a dimmer switch the body uses to keep various systems in balance.

There are two main receptors. CB1 receptors sit mostly in the brain and nervous system. This is where the "high" comes from, and also many of the effects on pain, nausea and appetite. CB2 receptors sit mostly in immune tissue and the periphery, and are more about inflammation and immune signalling. Cannabis compounds work by nudging this existing system, which is why their effects are so wide-ranging, and so hard to pin down to one neat action.

THC and CBD: the two that do most of the work

The cannabis plant makes over a hundred compounds called cannabinoids, but two do most of the talking, and they behave very differently.

THC (tetrahydrocannabinol) is the one that gets you high. It binds directly to CB1 receptors in the brain, which is what produces intoxication. It also drives most of its useful medical effects, like easing nausea, lifting appetite and dampening some kinds of pain and muscle spasm. The catch is that you generally can't separate the medical effects from the intoxicating ones. With THC, feeling "off" or high is often part of the package, which matters for driving, work and daily life.

CBD (cannabidiol) is the one that doesn't get you high. It barely touches CB1, so it's non-intoxicating, and it works through a more roundabout set of actions on other receptors involved in things like anxiety, inflammation and seizure activity. It also appears to take some of the edge off THC. That's why a purified CBD medicine can be a powerful anti-seizure drug while causing no "high" at all, and why the everyday CBD sold in shops is a different, far weaker proposition again.

The rest, minor cannabinoids like CBG and CBN, plus the aromatic terpenes that give each strain its smell, are often bundled up in a popular idea called the "entourage effect": the claim that whole-plant cannabis works better than isolated compounds because everything acts together. It's a plausible idea and a favourite of the industry, but the evidence for it is thin. THIN

Why "medical" doesn't always mean "high"

One of the most useful things to understand is that the effect depends heavily on which cannabinoids a product contains and in what ratio. A high-CBD, low-THC product can act medically without much intoxication. A THC-rich product will get you high whether it's from a clinic or the street. The molecule doesn't know the difference. So "medical cannabis" isn't one experience. It spans everything from a non-intoxicating epilepsy medicine to a THC oil that affects you much like recreational cannabis would.

That's also why dose and route matter so much. A few drops of oil under the tongue behaves very differently from a lungful of vapour. We cover that on How It's Taken. And it's why the honest question isn't "does cannabis work?" but "for what, at what dose, with what evidence?", which is exactly what the next page is about.