Oregano oil comes two ways, either pure or diluted with olive oil. If it is pure, then just use one drop at a time mixed well in 2 ounces of water. If it comes diluted by a half, then you can use two drops at a time, diluted to 1/3, up to 3 drops at a time, and so on. It is better to use less oregano oil at a time and take it more often. You can try grapefruit seed extract if you want. My experience with it is that it does a better job of causing side effects than of killing the candida. My advice is to use it as a last resort, and not a first choice. My first choices for fighting candida are the oregano oil and raw garlic. Raw garlic also helps to detoxify the body from mercury, and is an excellent source of sulphur. Raw garlic is also the least expensive antifungal.