The human body contains a specialized system called the endocannabinoid system (ECS), which is involved in regulating a variety of functions including sleep, appetite, pain and immune system response. – 1 

Studies have shown that CBD may help reduce chronic pain by impacting endocannabinoid receptor activity, reducing inflammation and interacting with neurotransmitters. – 2

References:

1- https://www.ncbi.nlm.nih.gov/pubmed/19675519

2- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5922297/