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I am very familiar with this. I am a double board certified US doctor with over 20 years of clinical, first-line experience. [see my profile].
It depends on what is wrong with the shoulder. If you don't know that, you need an orthopedic exam asap.
Realizing also that shoulder pain can come from the neck, so exam is needed there as well.
If it is arthritis, and in fact for most problems, physical therapy is needed as a mainstay of treatment.
In the meantime, heat, ibuprofen, rest, and a sling if needed.
If there are torn ligaments or tendons, sometimes surgery is needed.
If it is from disc problems in the neck, most often physical therapy is needed.
Let me know if you have more pertinent information and I can help you further.
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