Mailbox: will taking blood thinners prevent clots caused by the vaccine?

A sensible preventative measure, or a dangerous risk?
13 April 2021


A bottle of tablets


Paul’s been in touch with this question “If I take something for blood thinning before taking the covid vaccine, will that reduce my chances of getting a blood clot?” Chris Smith gives us the answer...

Chris - The answer is no, we're not advising people to do that. If people are already taking drugs like aspirin that have a blood thinning effect, you should definitely carry on taking aspirin. But you shouldn't start taking aspirin if you don't already, just on the off chance that you might suffer this side effect. And that's because A) it's an incredibly rare side effect that may not even be linked to the vaccine. We're still trying to prove that. But also the mechanism of action of drugs like aspirin is that they actually block the action of platelets. Well, the reason people have low platelets is because all their platelets have been activating and consumed to make these abnormal blood clots in the head. And if you therefore have a state of low platelets, having something that prevents the platelets you're left with working anymore could mean you're even more vulnerable to bleeding disorders and that could have even more catastrophic effects. So it's much safer not to take drugs that you're not already being advised to take by your doctor. But at the same time, as I've said, if you are already taking aspirin, you certainly shouldn't stop taking that. And remember, this is an incredibly rare side effect of around the order of one in a million, if it is caused by the vaccine at all.


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