Effects of analgesics on olfactory function and the perception of intranasal trigeminal stimuli.

BACKGROUND: There is some evidence suggesting that analgesics have an impact on human chemosensory function, especially opioids and cannabinoids are known to interfere with olfactory function. However, largely unknown is the effect of a long-term use of analgesics on the intranasal trigeminal system so far. Here, we investigated olfactory function and the perception of intranasal trigeminal stimuli in pain patients with long-term use of analgesics compared to age-matched healthy controls.

METHODS: For this purpose, a psychophysical approach was chosen to measure these sensory functions in 100 chronic pain patients and 95 controls. Olfactory testing was performed using the 'Sniffin' Sticks' test kit, which involves tests for odour threshold, odour discrimination and odour identification. Further, participants were asked to rate the intensity of trigeminal stimuli by using a visual analogue scale.

RESULTS: We observed that the chronic use of pain medication was associated with significantly reduced perception of intranasal trigeminal stimuli and olfactory function compared to age-matched controls without intake of analgesics. Results indicate that non-opioid and opioid drugs, or a combination of both did not differ in their effects on chemosensory function. Further, after eliminating the effect of a co-existing depression and the use of co-analgesics, the negative influence of analgesics on olfactory function and trigeminal perception was still evident.

CONCLUSION: The observed effect might be mediated due to interaction with opioid receptors in trigeminal ganglia and nuclei or due to trigeminal/olfactory interaction. As a practical consequence, patients should be made aware of a possible impairment of their olfactory and trigeminal function under long-term analgesic treatment. WHAT DOES THIS STUDY ADD?: We observed that the chronic use of pain medication was associated with significantly reduced olfactory function and perception of intranasal trigeminal stimuli compared to age-matched controls without intake of analgesics. Non-opioid and opioid drugs did not differ in their effects on chemosensory function.