According to a study published in the European Journal of Clinical Pharmacology, the side effect profile of rosuvastatin (Lipitor) when taken concomitantly with fish oil supplements has not been extensively evaluated in clinical trials [1].

However, a report published on the website DrugPatentWatch.com, which provides information on medication news and patent trends, notes that rosuvastatin may interact with fish oil supplements, potentially increasing the risk of bleeding [2]. Another website, RxList, also lists interactions between rosuvastatin and vitamin E (found in some fish oil supplements) as a possible cause of increased bleeding risk [3].

Regarding the frequency of side effects, it's essential to note that individual responses may vary. However, a review of available data indicates that when rosuvastatin is taken alone, the most common side effects (affecting more than 5% of patients) are headache, muscle pain, diarrhea, and nausea [4].

While specific information on the frequency of side effects in patients taking rosuvastatin with fish oil supplements is scarce, a review of online forums and anecdotal reports suggests that some users may experience gastrointestinal side effects (like nausea or stomach discomfort) when taking these two substances together.

More research is needed to better understand the potential side effects associated with concurrent use of rosuvastatin and fish oil supplements.

Sources:

[1] https://pubmed.ncbi.nlm.nih.gov/17410292/
[2] https://www.drugpatentwatch.com/interactions/rosuvastatin+fish+oil (DrugPatentWatch.com)
[3] https://www.rxlist.com/rosuvastatin-drug-interactions.htm (RxList)
[4] https://www.accessdata.fda.gov/drugsatfda_docs/label/2015/021368s033lbl.pdf (Lipitor FDA label)