Nearly 400 years ago, Robert Burton recommended the use of cannabis to treat depression in his book "The Anatomy of Melancholy." Although much of what Burton wrote can be disregarded -- for example, he claimed that spirits, witches, stars and magicians cause depression -- research is now supporting his treatment recommendation.
Depression is one of the most common mental health disorders in the world. The World Health Organization (WHO) estimates that 350 million people worldwide are affected by depression. In the United States, approximately 16 million adults, or about 6.9 percent of the population, have at least one major depressive episode each year.
According to the WHO, depression results from "a complex interaction of social, psychological and biological factors." Risk factors include:
Patients with major depression and bipolar disorder have been found to have structural changes in areas of their brains that control mood and memory, including the hippocampus, the thymus and the amygdala. In depressed patients for example, the hippocampus is smaller and the number of nerve cells are reduced.
Neurotransmitters, chemicals that relay messages between nerve cells, may also be affected by depression. This is the theory behind most anti-depressive medications today. For instance, low levels of serotonin, which helps regulate mood, sleep and appetite, have been linked to suicide. Selective serotonin uptake inhibitors, such as Paxil® and Zoloft®, help replace the missing serotonin.
The endocannabinoid system in the body produces chemicals that are involved in appetite, pain sensation, memory and mood, among other things. A recent study found that chronic stress reduces endocannabinoid production. This finding suggests that tetrahydrocannabinol in medical marijuana may help combat depression, caused by chronic stress, by supplementing lacking endocannabinoids.
There has been some [speculation](http://www.jstor.org/stable/2676359?seq=1# page_scan_tab_contents) that recreational marijuana is linked to depression, but researchers are now finding this may be related more to the state of the user prior to taking marijuana than to its actual use. In a large study of 4400 respondents, researchers found that occasional and chronic users of marijuana reported less depression than those who had never used the drug.
While Burton may have gotten his science wrong with regard to the causes of depression, his anecdotal evidence of the effects of cannabis on depression are now proving valid.