Are you on antibiotics? GSE increases the concentration of Doxycycline in your blood, so if you are on antibiotics, check with your Dr before adding anything.
I am on GSE (along with Biaxin and Bactrim, so you know it's ok with those abx). I take it in liquid from, because I was told it is absorbed better that way, and because you have more control over how much you take. It's possible to have herx reactions to GSE, and if you take the pill form, you have to start off at a fairly high dose.
I started off at 5 drops 3x a day, but you can start as low as you want. I now take 15 drops 3x a day. You need to take it in liquid, to dilute it. And it doesn't taste very nice. For 15 drops, I usually use about 500ml (2 cups) of water. You can do it with less, but there is a point where it starts to burn your throat.
You can get it at most health food stores. I was told the the Citricidal or nutribiotic brands were the best, but I don't know if you have them in the US. If not, look for a type that says it is made of, or using, citricidal. And don't get mixed up and get grape-seed extract by mistake!