The body’s endocannabinoid system (ECS) is perhaps the most important physiological system involved in establishing and maintaining our health.
The ECS plays a key role in regulating our physiological and cognitive processes and it’s purpose is to achieve homeostasis or ‘inner balance'.
Every mammal, not just humans, but animals including dogs, cats, horses, birds, fish and reptiles have an endocannabinoid system.  Humans produce their own cannabinoids, so called endocannabinoids from before we are born throughout our lives.  The best known human produced cannabinoids are 2AG and Anandamide (named after the Sanskrit term “Ananda,” which translates to “peace”). Anandamide is also called the 'bliss molecule'. It is becoming apparent that having healthy Anandamide levels is beneficial for our inner harmony and feeling of happiness.
The endocannabinoid system is part of the central nervous system. It is a network of receptors spread throughout our entire body.
The ECS has been recognised as an important body system affecting function of the brain, endocrine, and immune tissues. It also appears to play a very important regulatory role in the secretion of hormones related to reproductive functions and response to stress, affects appetite, food intake, energy balance and gastrointestinal tract activity. More conclusive evidence is coming to light supporting the theory of clinical endocannabinoid deficiency (Dr Ethan Russo), particularly for disease such as migraine, fibromyalgia, and irritable bowel syndrome. Given the large number of diseases which have shown endocannabinoid abnormalities such as epilepsy, cancer and a wide array of neurodegenerative diseases: it is an area which will undoubtedly and hopefully be explored further by the scientific community. 
Interestingly we are not aware of any other plant that has a whole physiological system dedicated to it in all mammals.  The cannabis plant is unique in this respect as we cannot get cannabinoids to support our ECS from any other natural food source in significant amounts.