Anorexia nervosa is a common complication of malignancy and is clinically manifested by mindless eating. Prolonged anorexia will likely cause weight loss and malnutrition. Anorexia can be caused either by the malignancy itself or as a side effect of various treatments such as surgery, radiotherapy and chemotherapy, which can make many anti-tumour treatments impossible.

Marijuana is known to cause hunger, but researchers at Washington State University have discovered through a series of animal studies that there is a mechanism in the brain that promotes appetite.

The discovery, detailed in the journal Scientific Reports, could pave the way for treating appetite disorders, anorexia and potentially obesity faced by cancer patients.

After exposing the mice to vaporised cannabis, the researchers used calcium imaging (similar to brain MRI) to determine how their brain cells responded. They observed that when the rodents anticipated and consumed the tasty treat, the cannabis activated a group of cells in the hypothalamus that were not activated in the mice that were not exposed to cannabis.

"When the mice were injected with marijuana, neurons that are normally inactive became active," said Jon Davis, corresponding author of the paper and assistant professor of neuroscience at Washington State University. "Something important happens in the hypothalamus after smoking vapour cannabis."

Calcium imaging has been used by other researchers to study the brain's response to food, but this is the first time it has been used to understand these characteristics after cannabis exposure.

As part of the study, the researchers also determined that CB1 receptors (a known cannabis target) control the activity of a well-known group of "feeding" cells in the hypothalamus called Agouti-associated protein neurons. Armed with this information, they used a "chemogenesis" technique, which acts like a molecular light switch that locks onto these neurons when the animal is exposed to cannabis. When these neurons are switched off, cannabis no longer promotes appetite.

Davis said, "We now know one way the brain responds to recreational marijuana to promote appetite."

This work builds on previous Davis Lab research on cannabis and appetite.

The Davis lab was one of the first to use whole vaporised cannabis plant matter in animal studies rather than injected tetrahydrocannabinol, with the aim of better mimicking the way humans use cannabis. In previous studies, researchers found genetic changes in the hypothalamus in response to cannabis, so in this study, Davis and his colleagues focused on that region.

Current research is supported by the Alcohol and Drug Abuse Research Program, the National Institute on Alcohol Abuse and Alcoholism, and the U.S. Department of Agriculture, as well as funding from Washington State Initiative Measure 171.

When treating cancer patients, industrial hemp therapies tend to fall into two distinct modalities - using industrial hemp to reduce symptoms and improve treatment tolerance, or using industrial hemp (often in high doses) to help kill the cancer. These two goals are not mutually exclusive, but each requires a different method of delivery.

When used properly, industrial hemp is a safe and effective treatment for cancer patients suffering from chronic pain, insomnia and chemotherapy-induced nausea and vomiting. Animal studies have shown that cannabinoids can prevent the development of neuropathic pain. This is a common side effect that can affect a patient's chemotherapy dose or course of chemotherapy. Even after the cancer is in remission, many patients still suffer from potentially permanent debilitating neuropathic pain.

Medical cannabis can help patients tolerate conventional cancer treatments such as chemotherapy and radiotherapy, and can be used in conjunction with these treatments with little likelihood of drug interactions. This means that there is little reason to avoid combining industrial hemp with conventional cancer treatments.