I assume you mean 20mcg pills. My advice is to increase the dose slowly until you know how your body reacts to it. Clen has a fairly long half life, so even if you take the same dose every day (say 40mcg) your blood levels will keep increasing. So you might get a bad surprise if you bump up your dose too fast. That having been said, I suggest you start with 40mcg (or 20mcg if you want to be conservative) and then increase the dose by 20mcg every 3-4 days until you hit 120mcg or start noticing sides (whichever comes first).