A chemical found in marijuana stops cancer from spreading, at least in cell cultures.
CBD may help prevent cancer from spreading, researchers at California Pacific Medical Center in San Francisco reported in 2007.
Other very preliminary studies on aggressive brain tumors in mice or cell cultures have shown that THC and CBD can slow or shrink tumors at the right dose, which is a strong reason to do more research.
One 2014 study found that marijuana can significantly slow the growth of the type of brain tumor associated with 80% of malignant brain cancer in people.
Still, these findings in cell cultures and animals don't necessarily mean the effect will translate to people — far more investigation is needed.
It may decrease anxiety in low doses.
Researchers know that many cannabis users consume marijuana to relax, but also that many people say smoking too much can cause anxiety. So scientists conducted a study to find the "Goldilocks" zone: the right amount of marijuana to calm people.
According to Emma Childs, an associate professor of psychiatry at the University of Illinois at Chicago and an author of the study, "we found that THC at low doses reduced stress, while higher doses had the opposite effect."
A few puffs was enough to help study participants relax, but a few puffs more started to amp up anxiety. However, people may react differently in different situations.
THC may slow the progression of Alzheimer's disease
The 2006 study, published in the journal Molecular Pharmaceutics, found that THC (the active chemical in marijuana) slows the formation of amyloid plaques by blocking the enzyme in the brain that makes them. These plaques kill brain cells and are associated with Alzheimer's.
A synthetic mixture of CBD and THC seems to preserve memory in a mouse model of Alzheimer's disease. Another study suggested that a THC-based prescription drug called dronabinol was able to reduce behavioral disturbances in dementia patients.
All these studies are in very early stages, though, so more research is needed.
The drug eases the pain of multiple sclerosis.
Marijuana may ease painful symptoms of multiple sclerosis, according to a study published in the Canadian Medical Association Journal.
Jody Corey-Bloom studied 30 multiple sclerosis patients with painful contractions in their muscles. These patients didn't respond to other treatments, but after smoking marijuana for a few days, they reported that they were in less pain.
The THC in marijuana seems to bind to receptors in the nerves and muscles to relieve pain.