I am fairly sensitive to medications, often requiring a smaller dose than is recommended for my weight. When my doctor and I decided that hormone replacement therapy might be a good option for me (due to heavy bleeding, among other concerns), I started taking the lowest commercially available dose of progesterone. I became foggy, sleepy, lethargic, and had a hard time just getting through the day. After several weeks it became clear that my body was not going to adapt, and we tried a smaller dose, which has to be compounded. (The commercially produced progesterone capsules are oil-filled, and cannot be split.) Mental clarity and energy returned, and I have been thriving ever since.