My fish is dying of old age. He's obviously in pain. If I crush up some pain killers and give him a tiny amount will it help with the pain?

Or will it just kill him faster. And what about a cc of alcohol. Again, don't wanna kill him immediately just take the pain away so he can die more peacefully.
Update: Update: In a lab in bio in college we were studying fish that were dosed with fluoxetine, so i know they have similar neurological systems to us.
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