What could cause sharp pain under the right shoulder blade?

Referred Pain? The same nerves that innervate the diaphragm go to the shoulder, as well. Therefore, anything that irritates the diaphragm, such as gallbladder or liver problems, can be "referred" to the shoulder. If the only symptom is shoulder pain (ie, no abdominal pain, nausea, vomiting, etc), I would search for other causes such as a muscle pull, arthritis.

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What medication can I take for the sharp pain under my shoulder blade on my right side What could cause sharp pain under the right shoulder blade?

Pain. Pain below the shoulder is very likely muscular. It is possible you may have a pulled muscle causing sharp pain. However, at your age there are several other possibilities such as shingles. Please see your doctor for proper evaluation. Also, note any other symptoms such as shortness of breath, sweating, burning pain etc.