Is Aspirin a Blood Thinner?

Aspirin has long been famous for its role in heart disease prevention and treatment. But for many people, one area of confusion is whether or not it counts as a blood thinner.

So, let’s clear things up right away: Yes, aspirin is a blood thinner.

That means it can help keep blood clots from forming spontaneously in your blood vessels. But it works a bit differently than some other blood thinners. And like all meds, even though it has benefits, it carries risks, too.

Interventional cardiologist Rishi Puri, MD, PhD, explains exactly how aspirin works and why its use requires the careful guidance of a healthcare provider.

How aspirin thins your blood

Aspirin stops platelets from clumping together to form blood clots. This “thins” your blood and helps reduce the risk that blood clots will form when they ordinarily shouldn’t.

Your blood doesn’t physically get “thinner,” Dr. Puri clarifies. Instead, it can flow more easily through your arteries. “Platelets are less likely to become spontaneously activated to form a clot within an artery — or even within a stent implanted in an artery,” he says.

Platelets are cells in your blood that help cause clots to form immediately when you’re injured. “They act like your body’s natural bandage and are a crucial part of the immediate healing process,” Dr. Puri explains. “But sometimes, platelets can spontaneously become activated to clump together and form clots at times when you don’t need them. These clots can block blood flow and lead to serious issues, like a heart attack or stroke, or even clog a stent.”

When people use the broad term “blood thinners,” they’re referring either to antiplatelet medications or anticoagulants. Aspirin belongs to the antiplatelet group. The meds in this group all work by stopping platelets from clumping together.

“Aspirin is the most commonly prescribed antiplatelet agent,” he adds.

Anticoagulants, on the other hand, don’t target platelets. Instead, they act in other ways that affect what healthcare providers call the “clotting cascade.” This refers to a series of steps, including enzyme reactions, that need to happen for a clot to form.

“We use antiplatelet medications and anticoagulants together in certain circumstances,” Dr. Puri further explains. “Sometimes, it’s just one or the other. It depends on what we’re treating or trying to prevent.”

Guidelines for use

If your healthcare provider prescribes aspirin for you, it’s crucial to closely follow their guidance. If you skip doses, aspirin may not work as it should. On the other hand, taking too much can lead to dangerous complications, like bleeding (more on that in a bit).

Your provider may advise taking aspirin for:

• Primary cardiovascular disease prevention: This means you’ve never had a heart attack or stroke and are trying to keep it that way.
• Secondary cardiovascular disease prevention: This means you’ve had a major cardiovascular event, like a heart attack, stroke or stent placement. Now, the goal is to help prevent more events.
• Heart attack first aid: Aspirin can be lifesaving during a heart attack.

Dr. Puri explains how aspirin can help in each scenario.

Primary prevention

In the past, healthy adults took a baby aspirin a day to help keep heart attacks away. But today, the guidelines are stricter.

“We only prescribe daily aspirin therapy for people who are at high risk for heart attacks or strokes,” Dr. Puri clarifies. “This usually means your risk is at least 10% to 15% over the next 10 years. In these situations, aspirin can greatly lower the odds, and the benefits of taking it outweigh the risks of bleeding from it.”

Before going further, a quick terminology check:

• The terms “baby aspirin” and “low-dose aspirin” typically refer to an 81 milligram (mg) tablet.
• “Daily aspirin therapy” means taking one baby aspirin (low-dose aspirin) every day to support your heart and blood vessel health.

Secondary prevention

Aspirin can play a major role in preventing heart attacks and strokes once you’ve already been diagnosed with heart disease. In fact, secondary prevention is the most common reason providers prescribe aspirin, Dr. Puri reports.

“Your doctor may start you on aspirin along with another blood thinner,” he says. “After a certain amount of time, they may remove the other medication and just keep you on aspirin going forward. Sometimes, they may do the reverse — they stop the aspirin and keep the alternate blood thinner going. That’s becoming increasingly common.”

You may also need to take aspirin if you’ve had a tissue valve implanted in your heart. This can reduce the risk of clots forming on the valve.

Heart attack first aid

When you’re having a heart attack, aspirin can help keep any existing clots from getting bigger. This lets some blood continue to reach your heart.

“Don’t delay calling for help,” Dr. Puri urges. “But while you’re on the phone, take an aspirin — not a baby dose, but the full dose of 325 mg. If you don’t have any on hand, first responders will likely give you an aspirin on the way to the hospital.”

Of course, this doesn’t apply if you’re allergic to aspirin. In that case, talk to your provider about the first aid they recommend so you can be prepared.

Risks of taking it

Aspirin can be lifesaving, but it comes with risks, especially when taking it long term.

“GI bleeding is the most common risk,” Dr. Puri says. “Aspirin can erode the GI tract, which makes bleeding more likely.”

This can happen to anyone who’s taking aspirin. But you face an increased risk of bleeding if you:

• Have conditions like peptic ulcer disease, esophagitis or polyps
• Are taking aspirin along with another blood thinner or an NSAID
• Have frailty or a tendency to fall
• Take higher doses of aspirin than prescribed

“We always need to consider these risks when prescribing aspirin,” he continues. “We only use it when the benefits outweigh the risks. And we appropriately adjust dosing of aspirin — as well as any other blood thinners — to keep you as safe as possible.”

These risks are why healthcare providers don’t recommend taking aspirin for aches and pains. While aspirin is technically a blood thinner and an NSAID, Dr. Puri clarifies that providers rarely advise using it for pain relief or inflammation these days.

“We mostly use aspirin for its antiplatelet effects, not for pain relief,” he says. “If you’re looking to manage issues like headaches or arthritis, talk to your provider about the best options based on your health and any other medications you’re taking. They may suggest a pain reliever like ibuprofen or acetaminophen (Tylenol®).”

Consult with your healthcare provider

Aspirin may help you prevent heart disease — but that’s not something you should decide on your own. Always check with a healthcare provider first. Just because a friend or family member takes aspirin doesn’t mean it’s appropriate for you.

If your doctor prescribes daily aspirin, here are some tips for using it safely:

• Take it at the same time every day, ideally with food.
• Don’t skip any days.
• Add it to your medications list (and always carry the list with you).
• Never stop taking aspirin without asking your provider first.

“Aspirin helps many people avoid dangerous blood clots that can lead to heart attacks and stroke,” Dr. Puri observes. “But it’s important to talk with your doctor about whether it’s right for you. Taking aspirin without a real need can do more harm than good.”