A study, by Dr. Stephens, was done with 64 undergraduate volunteers. The volunteers had to write down 5 words they use when in pain after running into a table and five words they would use to describe the table. They then had to put their hands in a bucket of ice cold water for a prolonged period of time; they first could repeat any swear word of their choice, then switching to a word they used to describe the table. Results showed that the volunteers could keep their hands submerged in the cold water for longer periods of time when they were repeating the swear word, showing a noticeable link between pain and increasing pain tolerance.
I could only find one study. I first came across this from the TV show Mythbusters. From my point of view, it would make sense that swearing reduces pain. Whenever I injure myself by running into a wall or table, or even burn myself, I curse and swear like nobody’s business. I guess, since I am so focused on cursing, I don’t really notice the pain after a few seconds. I definitely believe more research should be done on this subject to truly confirm that swearing increases.