If being on birth control raises the risk for a blood clot, why don't doctors suggest low dose aspirin therapy?

My understanding (perhaps I'm wrong) is that low dose aspirin therapy helps reduce the incidence of blood clots. Would it not work in this scenario where a woman is on birth control? I understand not all women are as high of a risk to get a blood clot from BC as others, but would taking the aspirin in any way help or would it be a bad idea? If being on birth control raises the risk for a blood clot, why don't doctors suggest low dose aspirin therapy?
This is actually a really interesting question, and unlike the posts above, I'm not going to discount that aspirin would help reduce the risk. The fact is, I just don't know and I'm pretty sure nobody else does either. This hasn't been looked at in a scientific experiment that I'm aware of.





There are a couple of reasons that I can give you for why it wouldn't have been studied at this point.





First of all, there is a mechanistic issue. By ';mechanistic issue'; I mean to describe that there are some relevant differences between the situation where aspirin is known to be helpful and the risk issues involving clot formation in women on oral contraceptives.





Aspirin is a medication which inhibits an enzyme known as ';cyclooxygenase'; which is responsible for one of the steps in the formation of a normal physiologic chemical type called prostaglandin. Prostaglandins are involved with the inflammatory process and the mediation of pain from the site of inflammation. Inhibiting them reduces pain and inflammation. Prostaglandins are also involved in the formation of platelet plugs. Platelets are tiny cells in the blood stream which glue together and plug holes. Inhibiting prostaglandins involved with platelet plug formation reduces the effectiveness of the platelet plug.





It turns out that for people with a vascular disease called atherosclerosis, one of the mechanisms that can lead to heart attack is that there can be ';atheromas'; which are also called ';plaques'; which are in the lining of the coronary arteries of the heart. These plaques can rupture. The surface gets a crack in it, and the platelets treat this as a hole. They plug the hole. Unfortunately, in these tiny blood vessels the plug can either totally block the narrowed artery right there, or they can break loose and float downstream until they block the artery farther on.





Partially inhibiting the platelet plug formation process with a low dose of aspirin is shown to reduce the heart attack rate in patients with elevated risk, and the side effects or complications from this plan are minimal. The benefits outweigh the risks.





Clot formation in women on oral contraceptives is a completely different phenomenon. These clots are much bigger. They're not associated with ruptured atherosclerotic plaques, and most importantly they happen in the VEINS! They mostly occur in the deep veins that are much larger in size. A clot that forms in a deep vein is called a ';deep vein thrombosis'; or DVT.





Venous thrombosis is an injury and a health risk for completely different reasons than ruptured plaques. Venous clots that occur in the veins of the leg, for example, can grow very very large. This is one of the most common places for them to form. They can be well over a foot long and easily a half inch in diameter or more. When they block the blood flow, they cause generalized swelling, but they don't cut off blood flow to the region. This is because they're blocking the EXIT and not the ENTRANCE to the tissue. ;)





The really concerning thing about clots in the leg veins is that they can break loose from where they started growing, and they can float in the blood stream back to the heart. In general, they'll get pumped through the heart without difficulty, no matter how big they are. However, the next organ in the flow pattern is the lungs. Here, the blood vessels branch again into a rich network of small vessels so that oxygen can be absorbed from the lungs. The branching network catches the clots and they block flow.





The sudden blockage of flow from the heart to the lungs will suddenly interfere with oxygen absorption and will lead to urgent illness. In bad enough cases, the oxygen deprivation can lead to death. In some cases the clot can be so big and can block so much flow, that there's no time for the oxygen levels to get low, and the heart finds itself pumping against so much resistance that it fails completely. This leads to a sudden cardiac death.





A clot that floats to the lungs is called a ';pulmonary embolus'; or PE for short.





There are a number of things that have to occur for otherwise normal blood to spontaneously clot in a vein. One of them is the creation of something called a ';hypercoagulable state';. This just means that the conditions in the chemistry of the blood have to be more apt to form clots than normal. The biology of hypercoagulability involves a system in the blood stream called the ';clotting cascade'; which is a family of ';clotting factors'; which are protein molecules that turn into clot when activated. They're related to, but not dependent on platelets. In the case of DVT associated with oral contraceptive use, the implication is that abnormally high levels of factor VII are produced.





As an apparent result of inducing higher than normal levels of factor VII, oral contraceptives cause a mildly hypercoagulable state. In some women who may have other undiagnosed conditions that also lead to hypercoagulability or who have occasional transient states that increase coagulation, the oral contraceptive may be enough to trigger a DVT.





The other things that contribute to clot formation are things like injury to the lining of blood vessels (to start the process) and slowed flow in the vessel (which helps the process propogate without impedence). The treatment of patients with serious problems of hypercoagulability does not involve the inhibition of platelets. It involves the inhibition of clotting factors.





So, this is what I referred to as the mechanistic issue. The reason that aspirin is helpful is that it inhibits platelet plug formation and patients with atherosclerosis have a problem with platelet plugs. On the other hand, women on oral contraceptives do not have a problem with platelet plugs, and instead have a problem with DVT which is not strongly related to the activity of platelets, but instead, clotting factor proteins.





Could it be that aspirin helps ANYWAY? Absolutely. This is, so far, an entirely theoretical consideration of the issue. To actually study it would require putting women who are already on oral contraceptive medication on either aspirin or sugar pills and then seeing if there was a decreased rate of clot formation in the treatment group. We'd have to do an experiment. This would actually be a valid and a safe thing to do. I expect that if someone wanted to do this, there would be no problem getting all of the important ethical and practical issues worked out.





When we do experiments like this, one of the things we have to build into the study is something called ';power';. The power of a study is defined by a mathematical evaluation of the statistics. It basically describes how small of a treatment effect can be shown by the study, given how many experimental subjects and data points are involved.





If a health phenomenon is comparatively rare to start with and we want to try to make it even RARER, then we would need a very powerful study. This means it would have to involve very large numbers of patients. In this case, it would be thousands! This is because the overall rate of DVT in reproductive age women is going to be about 5-10 per 10,000 including both those who are and those who are not on oral contraceptives. The rate is low, either way. If it takes studying a thousand women in order to have one DVT, then it's going to take many thousands in order to have a collective risk of some number of DVTs. It will take several thousands of women in EACH GROUP, with or without the aspirin, if we're to demonstrate that the risk of DVT is reduced by aspirin use.





If aspirin were a brand new drug and the company making it had some interest in trying to prove that it works this way, they might choose to help fund such a study. However, that's not the case. Aspirin is ancient, and any company can make it. The only way that a study like this could be done is if the financing came from a university or the NIH or some other source of research money.





What does it take to get a research grant to study a medical question?





It's not complicated.





All you really have to do is propose a decent theoretical argument that your experiment would yield results of interest.





Unfortunately, in this case, we have the opposite. In theory, the use of aspirin works on a different aspect of the clotting mechanism than is at issue with DVT in oral contraceptive use.








I hope that helps.





Really really good question!If being on birth control raises the risk for a blood clot, why don't doctors suggest low dose aspirin therapy?
It's a good question. The answer is because there are risks and benefits to both therapies, but they don't necessarily cancel each other out.





In the case of birth control, the risk of clotting is less than the risk of carrying a pregnancy in most women. In women who smoke, who are over 35, or who have underlying clotting issues or other medical problems, the risk of blood clots is different and is unacceptably high. So those women are recommended against using certain forms of birth control.





Taking aspirin every day, even low-dose aspirin, also carries risks--the risks of bleeding, of gastric problems, of interactions with other drugs and of allergic reactions, to name a few. You don't want to compound two risks instead of eliminating bothl. So that is why it's not a good idea. Yes, it would probably lower the risk of a clot, but at the cost of all those other risks that could be avoided.





In other words, why take two medications, both of which can have side effects, instead of just using a different method of birth control?
I'm not a doctor, but even I understand that aspirin does more than help reduce the incidence of blood clots. So you have to consider how it will react on the person in other ways, and with the different types of medications they may be taking. You can't just point out one possible benefit of something and think that's all there is to it. That's what too many people do and then they have to deal with all of these other affects which they never considered. They'll take one thing for a certain problem, but because it has a side affect or two then they'll take something else to try to counter that, but then that has some side affect, too. So they keep taking something else to counter some other affect of something they are already taking, and the meds just keep building up.
Because if you take aspirin everyday for years at a time, by the time you hit 55 your skin is exactly like microfilm. Really thin Really breakable, and really easy to bust your bloodvessels.


SO! Your suggestion would do more harm than good, but good try regardless.