Unnecessary risk

The birth control pill increases the risk of thrombosis. This is now well known. But how high the risk is varies greatly between the different preparations. A study by the Leibniz Institute for Prevention Research and Epidemiology – BIPS now shows the risks for new birth control pills and proves that many young women in Germany are prescribed pills with an unnecessarily high risk of thrombosis.

In their study, the scientists compared the risk of so-called venous thromboembolism between nine combined oral contraceptives. Since these are reimbursable in Germany for girls and young women, health insurance data can be used to estimate the thrombosis risk of the different preparations in this age group. Overall, the study population included 677,331 girls and young women with a new prescription between 2005 and 2017, with a mean age of 16 years.

The study confirmed that the risk of thrombosis was twice as high for many of the newer preparations compared with older preparations containing the active ingredient levonorgestrel as the progestogen component. The study also showed this for preparations containing the progestogen components dienogest and chlormadione, whose thrombosis risk had previously been little studied.

The Federal Institute for Drugs and Medical Devices has already pointed out the differences in thrombosis risk between the preparations in so-called red-hand letters and recommended prescribing preparations with the lowest thrombosis risk. The study now showed that the proportion of new prescriptions for preparations with the lowest risk has increased since the period 2005-2007, but is still very low. For example, in the 2015-2017 period, the proportion was only 54 percent, whereas 33 percent of prescriptions were for preparations with the highest risk of thrombosis.

"Our study confirms that the combination of levonorgestrel with low ethinyl estradiol has the lowest risk of thrombosis," explains Dr. Tania Schink, a scientist at BIPS and lead author of the study. She adds, "We were also able to show that the risk of thrombosis for the new chlormadinone-based pill variants is twice as high and thus in the same range as for desogestrel and drospirenone. So anyone who wants to keep their risk of thrombosis from the pill as low as possible should use a preparation based on levonorgestrel."

The data basis for the study was the pharmacoepidemiological research database GePaRD. It contains billing data from four statutory health insurers in Germany and includes information on approximately 25 million individuals at present. In addition to demographic data, GePaRD contains information on drug prescriptions as well as outpatient and inpatient services and diagnoses. Information on approximately 20 percent of the general population is available per data year, and all geographic regions of Germany are represented.

"Thromboses are indeed very rare events, especially in young women. Nevertheless, based on estimates by the European Medicines Agency, it can be assumed that two to seven additional thromboses per 10,000 users occur each year as a result of prescribing pills with a high risk of thrombosis instead of those with a low risk. These are cases of disease, some of them very severe, which could be prevented by a different prescription behavior," explains Prof. Dr. Ulrike Haug, last author of the study and head of the Department of Clinical Epidemiology at the BIPS.

Original publication

Schink T, Princk C, Braitmaier M, Haug U. (2022): Use of combined oral contraceptives and risk of venous thromboembolism in young women: A nested case-control analysis using German claims data, in: BJOG: An International Journal of Obstetrics & Gynaecology.

Further information and contact

Press release - Leibniz Institute for Prevention Research and Epidemiology (BIPS)