Library research reports from Sweden, England, and other countries have been studied in an effort to determine the effect of oral contraceptives (OCs) on lipoprotein metabolism. The results are conflicting, possibly due to the fact that there are different amounts of estrogen and progesterone in the various kinds of pills. Estrogen is known to cause increased glycerides in the blood, but progesterone can reduce the concentration of the glycerides. Blood lipids and glycerides increase after taking OCs, and high density lipoproteins decrease. Cholesterol and phospholipids usually decrease, but reports on this are also conflicting. It has been widely reported that OCs increase the risk of heart disease, but data from Great Britian indicate that the pills may actually protect the user from heart disease. Because the results of the aforementioned research are not conclusive, in depth research should be carried out to determine the relationship between OCs and lipoprotein metabolism. All clinical tests regarding OCs should take this relationship into consideration, in order to gather large amounts of reliable data.