Intranasal lidocaine has some evidence that it can provide a rapid relief of some trigeminal autonomic cephalalgias (TACs0, such as cluster headache, with few adverse events. Intranasal lidocaine may be helpful in the treatment of acute migraine and cluster headache because it blocks the sphenopalatine ganglion (SPG), the largest of 4 parasympathetic ganglia associated with facial pain via the trigeminal nerve. The SPG has preganglionic parasympathetic fibers that interact with postganglionic axons, vasodilator and secretory fibers of the trigeminal nerve and may contribute to migraine pain by releasing neuropeptides that increase parasympathetic cranial blood flow. Because the SPG is the only ganglion exposed to the environment via the nasal mucosa, researchers became intrigued by the idea of intranasal delivery of lidocaine to reduce parasympathetic outflow. For example, in a 2017 study of 100 patients age 15 to 55 who were seen in the emergency department for migraine, it was found that patients who received 7.5 mg of intravenous chlorpromazine plus 1 mL intranasal lidocaine achieved significantly better pain relief compared with those who received chlorpromazine plus 0.9% normal saline (placebo).
Chi, P. W., Hsieh, K. Y., Chen, K. Y., Hsu, C. W., Bai, C. H., Chen, C., & Hsu, Y. P. (2019). Intranasal lidocaine for acute migraine: A meta-analysis of randomized controlled trials. PloS one, 14(10), e0224285. https://doi.org/10.1371/journal.pone.0224285