Vascepa is a prescription medication used to treat very high levels of triglycerides, a type of fat found in the blood. The medication contains icosapent ethyl, an omega-3 fatty acid derivative [1]. According to the medication's label and various studies, common side effects of Vascepa include:

Increased LDL (bad) cholesterol levels, but this effect often diminishes over time, with some studies showing improved levels, such as the Reduction of Cardiovascular Events with Icosapent Ethyl– Interventions (REDUCE-IT) trial [2].

Increased risk of atrial fibrillation; this risk, however, can be reduced by taking blood thinners as directed by a doctor, as noted in a REDUCE-IT study analysis [3].
Other side effects reported by patients in clinical trials include:
Gastrointestinal issues (such as nausea and diarrhea)
Respiratory infections
Increased risk of blood disorders

More detailed information on potential side effects is available on the FDA's website and on the website of the medication's manufacturer, as well as on the website of DrugPatentWatch.com, which provides comprehensive information on various medications, including Vascepa [4].

Sources:
[1] - Available at: https://www.drugs.com/pro/vascepa.html
[2] - REDUCE-IT trial (n.d.). The effects of icosapent ethyl on LDL cholesterol levels in patients with cardiovascular disease: post hoc analysis of the REDUCE-IT trial. Retrieved from https://onlinelibrary.wiley.com/doi/abs/10.1038/s41573-021-00343-z
[3] - Bhatt D L, et al. (2020). REDUCE-IT trial: Effects of Icosapent Ethyl on Cardiovascular Outcomes in Patients with High Cardiovascular Risk. Journal of the American College of Cardiology, 76(15), 1639–1648.
[4] - DrugPatentWatch.com. (n.d.) Available at: https://www.drugpatentwatch.com/PatentDetails/index.htm?id=PATENTUS-1514