Cannabis Science

Does Smoking Weed Thin Your Blood?

blood samples

People use marijuana to solve some of their health woes such as migraines, insomnia, anxiety, and a host of other conditions. However, there are some side effects of marijuana that may be worrying for some people. For example, the link between marijuana and blood thinning. Since there is so much misinformation circulating about everything it makes sense to be skeptical. So, does smoking weed thin your blood? Here’s what we know. 

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Does Smoking Weed Thin Your Blood?

There isn’t a lot of information on whether or not weed thins the blood. 

However, there is evidence that weed can thin your blood based on a study. 

According to an animal study, Cannabis sativa, THC and CBD displayed anticoagulant effects in rats. That means it prevents clotting to some extent or thins the blood. 

The researchers concluded that weed could be useful for people who have type 2 diabetes. People with type 2 diabetes tend to have hypercoagulant states. That just means they’re more likely to develop blood clots. 

The fact that the study stated this means the researchers believe that maybe weed thins the blood and should be further studied.

There seems to be a lack of human studies investigating the anticoagulant effects of weed and their effects on humans. 

However, there is more information between smoking weed and the use of blood thinners. 

The Relationship Between Weed and Blood Thinners 

There is also concern that using weed with blood thinners can cause problems. 

NBC News states that around 2 million Americans with heart conditions have admitted to marijuana use. However, anticoagulants or blood thinners are common medications prescribed to people with heart conditions. 

Warfarin, a commonly prescribed blood thinner, is not recommended with cannabis use. A study called Interaction between warfarin and cannabis says “we suggest patients receiving Warfarin be warned against cannabis use.” The researchers believe further study needs to be done before giving the green light. 

The reason why the researchers had pause about mixing the two is because of cases of an increase in the international normalized ratio (INR) value. The INR value measures how long blood takes to clot. 

The study referenced several cases of an increased INR after using marijuana and blood thinners. In one case, bleeding was reported. 

In another case referenced by the study, the dosage of Warfarin had to be decreased by 30%. 

The takeaway from this is that people with heart conditions should have a frank conversation with their healthcare providers. That way the healthcare provider may be aware of the potential risks. 

Why Does Marijuana Interact With Blood Thinners?

A 2009 study posits that marijuana interferes with the metabolism of Warfarin. In addition to that, and to a lesser extent, marijuana also may displace Warfarin from its protein binding sites. 

NBC News also says, “Using [blood thinners] simultaneously with marijuana can change the effectiveness or the potency of the medications.”

Can Marijuana Cause Clots?


Dr. Carl Lavie told NBC News that THC can actually cause platelets to clot together, forming blood clots. These blood clots increase your risk for stroke and heart attacks. 

A study published in 2019 supports their viewpoint. The study stated that marijuana could cause platelet aggregation. Platelet aggregation refers to platelets clumping together and forming clots. 

Should People With Heart Conditions Avoid Weed?

It depends. 

NBC News says that people who had a heart attack or were hospitalized are most at risk. They suggest that these patients should either quit marijuana or limit its use. 

In addition to that, Dr. Sergio Fazio, a professor of cardiovascular medicine says that marijuana may affect your heartbeat. They were quoted on NBC News saying to pay attention to your heartbeat if you’re a stoner with heart conditions. 

Fazio says that heart palpitations can be dangerous for people who already have an existing heart condition. 

In addition to that, the 2019 study states that marijuana use can cause cannabis-induced vasospasms and cannabis arteritis.

Cannabis-induced vasospasm refers to contracting of the artery walls causing a decrease in blood flow. 

Cannabis arteritis refers to the damage of the arteries and damage to the walls of the blood vessels. This is more of a risk for heavy users of cannabis 

Benefits of Weed for the Heart 

While it seems like weed and heart health don’t mix, there is a glimmer of hope for stoners. 

Fazio told NBC News that if a little cannabis helps someone get enough sleep then it could be heart healthy. However, they were quoted saying, “When you move to the purely recreational use, that’s where the risks associated with heart problems potentially outweigh the benefits.”

How to Minimize the Risk of Weed Harming Your Heart Health

The best way to minimize the risk is by avoiding cannabis. However, that may not be suitable for everyone. 

The best way to use marijuana, according to Fazio, is by having an edible. Their reasoning is that smoking and using vape introduces other risks. 

Even though edibles may be safer, they’re not without risk. Lavie says you want to pay attention to the purity and dosage.

It’s best to opt for weed without contaminants. Lavie told NBC News, “A low dose of pure THC is safer than a high dose of THC that has many bad contaminants.”

If you’re thinking of utilizing synthetic marijuana, forget about it. NBC News posits that synthetic marijuana is much more potent and therefore more dangerous for people with heart conditions. They referenced a news story about how contaminated synthetic marijuana caused severe bleeding too. 


Does smoking weed thin your blood? There is evidence suggesting that it might. There needs to be more research done in this area. However, there seems to be more research about marijuana and heart health. 

Marijuana, in seemingly lower doses, can be harmless and maybe even beneficial for people with heart conditions. However, depending on the dosage, purity, and method of delivery, it could cause more harm than good. It’s best to discuss weed usage with your health professional if you have a heart condition.


About Trevann

Trevann is Stoner Rotation’s Jamaica-based lead writer for the Science section of our cannabis blog. She graduated with honors receiving her Bachelor of Science degree in Molecular Biology from the University of West Indies, Mona. For the last three years, she has covered some of the biggest questions around cannabis and health underpinned with research from supporting studies, medical journals and scholarly articles. Got something on your mind? You can reach her at [email protected].