People around America more and more are using cannabis as a treatment for nausea, from cancer patients trying to combat the nausea that follows chemotherapy to expecting mothers trying to keep food down in the months before birth.

As more is discovered about the endocannabinoid system, scientists are coming closer to pinpointing exactly why cannabis helps to reduce nausea.

Nausea is a necessary function of the body, used primarily to alert the body that something it ate might be poisonous or rotten and should be avoided now and in the future, or that the body is experiencing an illness or imbalance and needs treatment or rest. For example, dehydration can trigger nausea because the body is trying to send a signal that it’s unbalanced and needs more water.

But there are other factors, like motion or certain medications, that will also increase the signals being sent to the brain from the rest of the body, many of which the brain interprets as nausea.

Cannabis, when used to treat nausea, is not itself calming the digestive tract but rather controlling and reducing the signals that are being sent to the brain by certain receptors in the endocannabinoid system. This is the system in the body that responds to cannabis, regulating different things including appetite, memory and nausea. CBD and THC target different receptors in that system, to differing results.

Chemotherapy, for example, can trigger some receptors to send a signal to the brain that tells the body it is nauseous. Cannabis, when it interacts with the CB1 receptor in the endocannabinoid system, can reduce some of the signals CB1 receptors in the digestive tract send to the brain. Reducing those signals, in turn, reduces nausea and vomiting.

Synthetic CBD, in the form of the medicines nabilone and dronabinol, has been used to treat nausea for the last twenty years. Both products are approved by the FDA.