The endocannabinoid system is the body's own 'cannabis system'. There is a network of receptors (that switch on cells in the body) and affect the function of nerve cells. Chemicals found naturally in the body and in the cannabis plant affect the function of the nerve cells causing the potential positive effect on symptoms for a range of conditions. These chemicals are called cannabinoids. Research suggests some patients have low levels of cannabinoids which is possibly a reason why taking cannabinoids from cannabis is found helpful by some patients.