Progesterone is a sex hormone produced in significant amounts in women, especially during pregnancy that can enhance breast growth and stimulate other structures in the breasts, making them fuller and rounder with larger nipples. It may counter dryness caused by estradiol/spiro, help with brittle nails and give you softer, more elastic skin, softer hair as well. It may increase libido in a good way, help with sleep (or not, depending on the person), promote fat deposition, reduce anxiety, improve mood but not necessarily. It makes some hungrier, bloated but it can also reduce water retention in others. It is usually taken at night as it makes you tired, drowsy, especially at first.