How do they work?
‘Opioid receptors’ are proteins found on cells in the brain, spinal cord, gastrointestinal tract, and other organs, throughout the body. The feelings of pain are reduced once ingested opioids attach to these receptors.
There are a number of different types of opioid receptors, with the 3 most common types being μ, κ and δ (though there are many others). Different types of drugs are more effective for different types of opioid receptors.
RM, Hollingshead J, Cornblath DR. Tramadol for neuropathic pain.
Cochrane Database of Systematic Reviews 2006, Issue 3. Art. No.: CD003726. DOI: 10.1002/14651858.CD003726.pub3
McNicol ED, Midbari
A, Eisenberg E. Opioids for neuropathic pain.
Cochrane Database Syst Rev. 2013 Aug 29; 8:CD006146.