Opioids can be a life-changing medication for many patients with chronic pain, if used responsibly. Opioids have great potential to ease pain; however, they have equal potential for deadly side effects and misuse, as stated above.
Opioids mimic the actions of endogenous opioid peptides by interacting with mu, delta or kappa opioid receptors. Opioids work by binding to opioid receptors in the central and peripheral nervous system were they produce analgesic effects by decreasing the perception of pain, decreasing your reaction to pain, and increasing pain tolerance. They do not have an effect on the source of the pain, such as anti-inflammatory medications by reducing inflammation.
There are many types of nerve fibers in our body. The two main nerve fibers types that are involved in the perception of pain are known as C-fibers and A-delta fibers. When opioids bind opioid receptors located on these nerve fibers they block the release of pain neurotransmitters (through a complicated process which we do not need to discuss here—otherwise, you would fall asleep reading this). The blocking of these neurotransmitters (i.e., glutamate, substance P, and calcitonin gene-related peptide) from the nociceptive fibers results in analgesia (i.e., pain relief). Opioids also bind to other opioid receptors throughout the body, such as in gastrointestinal tract, producing unwanted side effects such as constipation, respiratory depression, and sedation. They also often produce euphoria, which is one of the reasons their use can lead to abuse, misuse and addiction.