.There is a medicine called levaza for high cholesterol . It is made from 100% unadulterated fish oil..
There are equally effective alternatives with hechsherim (even with the badatz) However, insurance will only pay for the prescription form.
Is it muttar to swallow it? it comes in a gelatin capsule.
You should buy the one with the hechsher. Firstly because most poskim hold that gelatin is not kosher unless it was made with a hechsher. Secondly, because the fish oil itself may be from a on kosher fish.
Igros Moshe Y:D 2-27, Minchas Yitzchok 5-5, Mishneh Halachos 3-111, teshuvos V’hanhagos 2-381, Emek Hateshuva 3-67, Shevet Halevi7-135.