If you have to add something to your oil, you're using the wrong oil. Oil formulas are carefully balanced. Don't upset that balance by playing backyard shadetree chemist with a supplement.
If you need additional ZDDP, there's plenty of oils out there that are already balanced around a higher concentration. Since application dictates chemistry, we also need to know what engine this oil is going in, the health of said engine, and how you plan to use it. Then we can give you some recommendations.