Look for “USP Certified”. NatureMade is a popular brand that tends to have this. Costco brand (Kirkland) also often does - note that Kirkland prices are cheap in Costco but not so much on Amazon (resold or something). If you have a Costco near you, it is a very cost effective way to get fresh food and supplements. It’s silly but it really helped me become healthier, because I stopped being hesitant about the price (I was raised in a not-well-off household... the mental barrier can be pretty strong even though it’s irrational vs wastes of money that are neutral or harm health, while nutrition is very helpful and a pretty good bang for buck)