Anticoagulants, commonly known as blood thinners, are prescribed to prevent dangerous blood clots that can lead to heart attack, stroke, or pulmonary embolism. These medications interfere with the body’s natural ability to form clots. For many people who menstruate, this systemic change significantly impacts their menstrual cycle. Changes in bleeding patterns are a common side effect, with studies indicating that up to 70% of women on oral anticoagulants experience heavy menstrual bleeding.
How Anticoagulants Affect Blood Clotting and Uterine Shedding
Anticoagulants interrupt the complex biological process known as the clotting cascade. They prevent the formation of fibrin, a protein that weaves together to create the stable, mesh-like plug that stops blood flow. Newer oral anticoagulants, such as Factor Xa inhibitors, work by directly blocking the enzyme Factor Xa, a key step leading to fibrin production.
Menstrual bleeding involves the monthly shedding of the uterine endometrium. The body normally uses localized clotting factors to control blood loss during this process. When systemic anticoagulation is introduced, it impairs the ability to form stable clots at the site of the uterine wound. This inability to quickly form a fibrin plug means the bleeding becomes less controlled, resulting in a heavier flow and a longer period duration.
Common Alterations to Menstrual Flow and Cycle
The most common alteration after starting blood thinners is an increase in the volume of menstrual flow. This heavy flow often translates to a longer period, sometimes increasing the average duration from five days to six or seven days. This increased bleeding is frequently accompanied by the passage of larger or more frequent blood clots.
Although the uterus naturally forms small clots during heavy flow, the medication’s inhibition of the clotting cascade can make these clots more numerous and larger. Some patients also notice an increase in intermenstrual bleeding, often called spotting, between their regular cycles. These changes can significantly affect a person’s quality of life, potentially leading to missed social activities or work.
Recognizing Signs of Dangerously Heavy Bleeding
It is important to distinguish between the expected increase in flow and dangerously heavy bleeding, medically referred to as menorrhagia. A primary warning sign is bleeding so heavily that a pad or tampon must be changed every hour or more often for several consecutive hours. Another sign of concern is the frequent passage of large blood clots, specifically those roughly the size of a quarter or a golf ball.
Excessive blood loss can quickly lead to anemia and requires immediate medical attention. Symptoms indicating severe anemia include severe fatigue, unusual shortness of breath, or feeling dizzy or lightheaded. If bleeding will not stop or slow down, or if you experience a sudden, severe headache, seek emergency medical care immediately.
Options for Adjusting Anticoagulant Therapy
For those experiencing problematic or heavy bleeding, the first step is to consult the prescribing physician. Patients should never stop their anticoagulant medication on their own, as stopping prematurely carries a high risk of recurrent, life-threatening thrombosis. The medical team may consider several strategies to manage the bleeding while maintaining clot prevention.
The medical team may employ several strategies to manage bleeding while maintaining clot prevention:
- Switching to a different type of anticoagulant, as agents like apixaban or dabigatran may be associated with a lower incidence of heavy menstrual bleeding compared to rivaroxaban.
- Adding hormonal therapy, such as the levonorgestrel intrauterine system (LNG-IUS), a local progesterone device that significantly reduces menstrual blood loss.
- Considering temporary dose adjustment of the anticoagulant in rare cases, only after the acute risk of clotting has passed and under strict medical supervision.
- Prescribing non-hormonal options, such as the antifibrinolytic agent tranexamic acid, to be taken only during the menstrual flow to help stabilize clots at the uterine lining.