Subsequently, synthetic progesterone was combined with oestrogen to protect the endometrium. Synthetic progesterone differs in composition from the progesterone naturally found in the body. Synthetic progesterone, derived from 'natural' progesterone, is chemically altered in a laboratory, resulting in the addition of other molecules. The altered molecular structure of progestins, however, appears to cause numerous side effects. Women taking progestins may experience weight gain, fluid retention, headaches, irritability and depression.
Some progestins also have adverse effects on cholesterol levels.
When they are taken with oestrogen in hormone replacement therapy, the progestins may reduce the cardiovascular benefits that oestrogen is believed to provide. Natural progesterone The term 'natural' is commonly used to describe something that comes from nature and is free of artificial substances. In the field of health, 'natural' has come to refer to treatments and therapies which use products sourced from nature. The term 'natural progesterone', therefore, is somewhat misleading as it suggests that the progesterone is derived directly from nature. In fact, natural progesterone is artificially produced in a laboratory.