Progesterone is a hormone and, as such, concerns about its inappropriate use have been raised. A physician should be consulted before using this hormone as a supplement. Few side effects have been associated with topical progesterone creams but can include skin reactions. Effects of natural progesterone on breast cancer risk remain unclear. Research has suggested both increased and reduced risk.

Synthetic progestins have many well-known side effects, including the increase of LDL (“bad”) cholesterol and the decrease of HDL (“good”) cholesterol. Other side effects reported with synthetic progestins include bloating, breast soreness, depression, and mood swings. Natural progesterone has been shown to have no adverse effect on HDL cholesterol levels.⁶ Overall, natural progesterone is considerably safer than progestins and is therefore preferred by many doctors in situations where either would be effective.⁷