There are many quality brands and probably a lot of not quality. Choose top companies like Jarrow, Source Naturals, Swansons brand is good, I used it for years...I mostly now go to Olympian Labs as it's a good price and high quality. Make sure to take enough for body weight, good starting point is 100mg for a little and while and move to 200mg...I can explain more if you'd like. Work with dosing for your body and needs. If you have a truly chronic issue, start higher that's called a loading dose.

Know that if one is taking Pharma blood thinner then can't take both...