Opioids

What are Opioids?

Opioids (narcotics) are one of the world’s oldest known drugs. They’re known, not only for their pain killing abilities, but for their side effects, including sedation and euphoria. 

While antidepressants and anticonvulsants remain the primary drugs prescribed in the treatment of neuropathic pain, opioids are also sometimes added on for this type of pain. Using opioids can be challenging for neuropathic pain because they don't have reliable beneficial effect and may present risks for dependency and addiction. 

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. 

What kinds are there?

• Analgesics (Oxycodone, Morphine, Fentanyl, Methadone and Levorphanol):
  Opioids are known for their rapid onset of pain relief after ingestion. One of the considerations for patients using analgesic opioids is constipation, a common side effect, will require some management. Additional side effects may include nausea, vomiting, drowsiness, dizziness and urinary retention. 
• Tramadol (Ultram): Tramadol is unique as it’s synthetically produced and chemically different than other opioids. Tramadol acts on serotonin receptors. For moderate pain, tramadol is similar in effect to morphine – though effectiveness decreases with more severe the pain. The most common side effects include dizziness, nausea, constipation, vertigo, headaches, vomiting and drowsiness.   Tramadol may also lower seizure thresholds which should be taken into consideration for patients diagnosed with epilepsy.   
• Tapentadol: Tapentadol is a low potency opioid that acts on norepinephrine receptors. 

Related evidence

Duehmke 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. doi: 10.1002/14651858.CD006146.pub2.