The most common side effect of strontium citrate is mild gastrointestinal discomfort and, in some cases, diarrhea. Other side effects are rare, according to WebMD.
Strontium is a trace element commonly found in soil and seawater, and mainly ingested through seafood. It's very similar to calcium and it's believed to aid in new bone formation and slow old bone breakage. Strontium may also help improve bone density, says WebMD.
A form of the element called strontium ranelate is available in some places of Europe and Australia for the treatment of osteoporosis. This form of strontium is not approved by the FDA, but strontium citrate is available over the counter, notes WebMD.