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As with any medications, there are side effects. You can have none, some or all of the below listed side effects:
dizziness, drowsiness, headache, diarrhea, constipation, excitability, weakness, anxiety, difficulty sleeping, upset stomach, rapid or irregular heart beat and/or decreased appetite.
To my knowledge, there are no known side effects of Alka-Seltzer related to the bones and or joints. Some antacids can cause osteopenia or osteoporosis, but these are ones that are aluminum based. Alka-Seltzer is not aluminum based.
I hope this has answered your question. If you have further questions regarding this, please reply to this post.
Have a great day!