I buy Now brand Gel Caps. Yes they are empty. For anal, I get 000, the largest size. I have a book on aromatherapy. It has an index. I looked up "vermifuge" in the index and made a list of all the oils recommended. I purchased as many of them as I could find. I mix and match the oils. Sometimes I use nutmeg, anise, cloves and things like that. Sometimes I use things like garlic, thyme, rosemary, etc. Sometimes I mix thuja, eucalyptus, tea tree, etc. I mix things that seem like they go together. Sometimes I just mix a bunch of them together. I rotate "formulas" just in case resistance is a real concern, which I doubt.