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Studies are executed with all sort of entertainment drugs, from MDMA to Ketamine with apparently some positive results. Hypnosis is also tested. I think Flare, the kinda new kid on the block for earplugs, mentioned at one stage, they like to create earplugs with the ability to cancel ringing ears. For those with a specific frequency, this can be done by creating the same frequency but 180 degrees shifted signal; Technology developed already a few decades ago for use in propeller airplanes to reduce the propeller sounds.

https://www.flareaudio.com/