Can Viagra cause blood clots?

Despite the fact that erectile dysfunction has a drastic impact on the quality of life for men, fears regarding the side effects of Viagra prevent many men from regaining their erections. One of the chief concerns of men contemplating taking the little blue pill is whether Viagra causes blood clots. While clotting is a life-saving mechanism to stop us from bleeding out from cuts, inappropriate or excessive clotting in the bloodstream can lead to heart attacks and strokes.

In this article, we’ll take a close look at the research to see if there’s any connection between Viagra use and blood clots.

Before we explore the potential link between Viagra and blood clot formation, it’s helpful to understand how erectile dysfunction affects the body and how Viagra works to address it.

Understanding erectile dysfunction: Causes, risks, and treatment

Erectile dysfunction (ED), also called impotence, is when a man can’t get or keep an erection firm enough for satisfying sexual activity [1].] Though there isn’t a strict time frame for diagnosing ED, many professionals suggest it should be a persistent issue for around six months. Erectile dysfunction is common, especially as men age, and its likelihood increases with certain health conditions [2].

Erectile dysfunction can sometimes signal underlying health concerns, such as heart disease, diabetes, high cholesterol, and high blood pressure [3]. Conditions that impact blood flow, nerves, hormone levels, or erectile tissue are often contributors. For example, endothelial dysfunction, which affects the lining of blood vessels, is commonly found in men with ED. Essentially, erectile dysfunction is like the canary in the mineshaft, warning you that your blood vessels might need attention [4].

While physical factors cause most cases of ED, mental factors can also play a part, especially for younger men. Even when erectile dysfunction has physical roots, it can lead to emotional stress, affecting confidence, relationships, and overall well-being. The good news is that erectile dysfunction is highly treatable, with many options available to help men regain confidence and improve their quality of life. If you have questions regarding erectile dysfunction, feel free to contact us at info@medicalmojo.co.uk.

How Viagra works

Like other medicines for erectile dysfunction, Viagra or sildenafil work by increasing the blood flow to the penis. They belong to a class of drugs called phosphodiesterase type 5 inhibitors (PDE5i), and they work by increasing the amount of a certain chemical in the body called cGMP [5].

When you have plenty of cGMP, you have more blood flowing into the tissues of your penis called the corpora cavernosa. Imagine the floodgates have been opened, and the blood rushes in, increasing the pressure within the penis until, voila! Erection! So, in a nutshell, Viagra or sildenafil increases blood flow, so it would seem paradoxical that it could, therefore, promote blood clots that would then block blood vessels. So, is there any truth to the association of Viagra with blood clots?

Viagra-associated deaths

A few cases of heart attacks and strokes, some fatal, in men taking Viagra have puzzled researchers. Initially, Viagra was developed as a potential treatment for angina, given its ability to widen blood vessels. However, the drug was not looking promising for its intended purpose, but a serendipitous discovery of one of its side effects changed the course of the drug’s history, turning it into a blockbuster drug. This side effect was its ability to cause erections.  By increasing cGMP levels by inhibiting its breakdown, it caused the widening of vessels, allowing more blood to flow into the penis. In addition, the prevailing thinking was that cGMP prevented platelets from aggregating. So, it was initially thought that Viagra would prevent clots, not cause them.

What are platelets?

Platelets are small, disk-shaped cells that move freely through the bloodstream. When a blood vessel is damaged, platelets become activated and develop sticky surfaces, allowing them to stick to each other and the injured site, forming a plug to help stop bleeding.

While platelet aggregation helps minimise the loss of blood when injury occurs, it can also lead to clotting that blocks a blood vessel — a life-threatening condition called thrombosis that can cause heart attack and stroke.

cGMP and platelets

Sildenafil, the active pharmaceutical ingredient in Viagra, belongs to a class of medicines known as phosphodiesterase type 5 inhibitors or PDE5i. They work by preventing the breakdown of a compound called cGMP, causing the widening of the blood vessels, which in the case of the penis, allows blood to flood in to cause an erection.

Before a 2003 study by Xiaoping Du and his colleagues at the University of Illinois at Chicago, the thinking was that cGMP prevented the aggregation of platelets. However, their research on a molecule called PKG, short for cGMP-dependent protein kinase, found that rather than preventing the aggregation or clumping of the platelets, this molecule made these platelets stickier [6].

The results were so surprising that the team questioned whether their lab cells might be behaving unusually. Like any good scientist, they had to test their theory. So, they tested the effects of Viagra on both mouse and human platelets, which showed the same sticky response. Further, they observed that platelets from mice lacking PKG didn’t clump as readily as those from normal mice, reinforcing their findings.

Location! Location! Location!

This is not just a mantra for real estate but, more importantly, for science. Often, what works in the lab or a test tube does not work in the body, and vice versa. This was what was happening with Viagra and the platelets. When alone together, the Viagra and platelets had little attraction to each other. But change the mood, add dimmed lighting and romantic music, and voila! Instant attraction. Obviously, that is not precisely what is happening in the body, but it gives you a good idea of context and location. What was happening was that when exposed to an environment that stimulated an injured blood vessel, such as hardening of the arteries, Viagra would cause the platelets to clump together.

To check this theory, the researchers tested the effect of Viagra on platelets. Alone, Viagra had no effect. But when exposed to an environment that simulated an injured blood vessel — as in the hardening of the arteries — Viagra caused the platelets to clump. This occurred even at levels well below that found in men taking Viagra. So, the long and short of it is that if someone with already damaged blood vessels takes Viagra, this clotting action may be enough to start causing problems.

In a news release, Xiaoping Du said:

“Viagra, by itself, probably is not sufficient to cause a heart attack in healthy people, but our research suggests that it may present a risk for patients with pre-existing conditions such as atherosclerosis.”

They found that, on its own, Viagra did not cause platelets to clump. However, when mixed with small amounts of other compounds typically present in damaged blood vessels, Viagra did promote clumping. This effect occurred even at concentrations lower than those found in patients taking Viagra for erectile dysfunction.

The researchers now think this potentially dangerous side effect of platelet clumping could be aggravated in men with hardening of the arteries.

cGMP and platelets, a revised theory

Building on previous research that suggested cGMP prevents platelet clumping, researchers at the University of Illinois at Chicago proposed a more nuanced role for cGMP. They believe it initially triggers platelets to clump together, helping seal a wound, but later reverses this effect to prevent excessive clumping that could block a blood vessel. For individuals at high risk of blood clots—such as those with narrowed or damaged blood vessels—this initial platelet buildup could still lead to problems.

Does Viagra cause blood clots in healthy men?

Given that Viagra raises cGMP levels by blocking an enzyme that breaks it down, Du and his team examined its effect on platelets from healthy donors. However, they found that Viagra or sildenafil had no effect and did not cause the platelets to clot and clump together. So, if you have healthy blood vessels, then taking Viagra is perfectly safe and will not cause the formation of blood clots.

Should you stop taking Viagra?

No, so long as you do not have any other risk factors. The researchers found that the impotence drug Viagra (sildenafil) may actually encourage potentially dangerous blood clots forming in men with certain risk factors.

What are these risk factors for increased clot formation when taking Viagra?

The researchers now think this potentially dangerous side effect could be aggravated in men suffering from hardening of the arteries. To learn more about who should not take Viagra, read the section “Who should not take Viagra?”.

New research on PDE5i and clot formation

Since that landmark paper in 2003, further research has led to a more nuanced theory about the relationship between cGMP and platelet aggregation. Before we explore this revised theory, let’s examine some of the other evidence researchers have uncovered regarding cGMP and the clotting process.

It has been reported that PDE5 inhibitors may attenuate the development of thrombosis in acute ischaemic stroke. The anti-thrombotic mechanism of PDE5 inhibitors is related to the inhibition of platelet aggregation through augmentation of the cAMP/cGMP/NO pathway [8].

A more recent study published in 2019 [9] found that sildenafil decreases the risk of acute ischaemic stroke by inhibiting platelet aggregation and intimal hyperplasia after angioplasty.

Researchers have also found that sildenafil blocks platelet activation induced by thrombin and adenosine diphosphate (ADP), mainly through the activation of cGMP-dependent protein kinase (cGK), since cGK inhibitors prevent sildenafil-induced platelet inhibition [9].

A 2001 study [10] observed that sildenafil could inhibit ADP and collagen-induced platelet aggregation; in addition, tadalafil mitigates dysfunction of the platelet-endothelial pathway in patients with erectile dysfunction [11].

Further research by Lewis et al. 2006 [7] found that when Viagra was given intravenously, it decreased the clumping of the platelets.

In reviewing their findings alongside previous scientific evidence that suggested cGMP prevents platelets from clumping, researchers now propose a two-phase effect of cGMP: initially, it promotes platelets to clump and seal a wound, then later shifts to prevent excessive buildup, which could otherwise block blood flow.

For individuals at risk of blood clots, such as those with already narrowed or damaged blood vessels, even this initial platelet accumulation could pose a significant health risk.

So, does Viagra cause clots?

It’s confusing, isn’t it? But this is how science works: a theory is proposed, and the theory holds until contrary evidence is found. As we have seen, the initial research, which came after concerns were raised about the safety of Viagra, led to the revised view regarding cGMP and the clotting process. The more simplistic view regarding the cGMP-dependent protein kinase and platelet aggregation has become more nuanced and is still evolving.

Who should not take Viagra?

So, what does it all mean? Well, the take-home message is that Viagra is generally safe and well tolerated but should not be used in the following categories [12].

Nitrates and low blood pressure: People taking nitrates (often used for chest pain or heart conditions) should not use Viagra because it can cause a dangerous drop in blood pressure. Nitrates and Viagra both affect a chemical in the body called cGMP, which helps widen blood vessels. When combined, they can cause a severe drop in blood pressure, potentially life-threatening. Generally, you should wait at least 24 hours after taking Viagra before using any nitrate medication. To learn more about why nitrates should not be combined with Viagra, read our blog, “Can Viagra cause a stroke?”

Other low blood pressure risks: If you have low blood pressure for other reasons, such as dehydration, Viagra may not be safe for you, as it can lower blood pressure even more.

Allergies and sensitivities: Anyone with known allergies to Viagra or any of its ingredients should avoid it to prevent a possible allergic reaction.

Specific health conditions to watch out for:

• Lung conditions: Viagra isn’t recommended for people with a lung condition called pulmonary veno-occlusive disease (PVOD), as it can worsen symptoms.
• Heart conditions affecting blood flow: Those with issues affecting blood flow out of the heart, like left ventricular outflow obstruction, should avoid Viagra due to potential blood pressure problems.
• Blood disorders: For people with pulmonary hypertension linked to sickle cell anaemia, Viagra is not recommended due to the risk of severe complications.
• Nervous system conditions: People with multiple system atrophy (a disorder that affects the nervous system) are at risk for dangerously low blood pressure if they take Viagra.
• Eye conditions: Those with a history of eye issues, such as optic neuropathy or genetic retinal disorders, should not use Viagra. If vision loss occurs, stop taking Viagra immediately and seek medical help.

Always consult a healthcare provider before taking Viagra if you have any of these conditions to ensure it’s safe for your situation. Or contact the team at medicalmojo.co.uk by emailing us at info@medicalmojo.co.uk.

Getting support and guidance for sexual health

When considering Viagra or other options for improving sexual health, talking with a healthcare provider is a smart first step. At Medicalmojo.co.uk, health professionals are ready to provide expert advice tailored to your individual health needs, helping you explore ways to boost sexual satisfaction. Open conversations about personal concerns can be crucial in making the right decisions for your sexual health, so don’t hesitate to ask questions and voice concerns. Professional support truly matters when it comes to using medications like Viagra.

Why choose Medical Mojo for sexual health support?

If you’re thinking about Viagra or ways to enhance sexual health, getting professional guidance ensures that any treatment is safe and tailored to your needs. Medical Mojo offers discreet, supportive telehealth services for men facing sensitive issues like erectile dysfunction. Their team of experienced pharmacists, doctors, and therapists provides advice on Viagra and other options, allowing you to make informed, confident choices.

Here’s why Medical Mojo is an excellent choice for sexual health support:

• Private, judgement-free consultations from home
• Personalised advice based on your full health profile
• Health screenings to confirm if Viagra is suitable for you
• Ongoing support and follow-up during treatment
• Clear guidance on realistic expectations with Viagra
• Holistic advice on lifestyle changes for better sexual health
• Access to evidence-based articles covering all aspects of sexual health
• Health and lifestyle coaching to help you get your mojo back
• Bespoke medicines compounded by our team of expert pharmacists

With Medical Mojo, you’ll get a clear understanding of what Viagra can and cannot achieve, helping you set healthy expectations and make informed choices. For more information, get in touch.

Disclaimer: This article is for informational purposes only and does not replace professional medical advice.

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References:

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3. Orimoloye OA, Feldman DI, Blaha MJ. Erectile dysfunction links to cardiovascular disease-defining the clinical value. Trends Cardiovasc Med. 2019 Nov;29(8):458-465.
4. Matsui H, Sopko NA, Hannan JL, Bivalacqua TJ. Pathophysiology of erectile dysfunction. Curr Drug Targets. 2015;16(5):411-9.
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7. Lewis, G.D., Witzke, C., Colon-Hernandez, P., Guerrero, J.L., Bloch, K.D. and Semigran, M.J., 2006. Sildenafil improves coronary artery patency in a canine model of platelet-mediated cyclic coronary occlusion after thrombolysis. Journal of the American College of Cardiology, 47(7), pp.1471-1477.
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9. Yang H-M, Jin S, Jang H, Kim J-Y, Lee J-E, Kim J et al. (2019) Sildenafil reduces neointimal hyperplasia after angioplasty and inhibits platelet aggregation via activation of cGMP-dependent protein kinase. Sci Rep 9(1):1–12
10. Berkels R, Klotz T, Sticht G, Englemann U, Klaus W (2001) Modulation of human platelet aggregation by the phosphodiesterase type 5 inhibitor sildenafil. J Cardiovasc Pharmacol 37(4):413–421
11. La Vignera S, Condorelli R, D’Agata R, Vicari E, Calogero A (2012) Dysfunction of the endothelial-platelet pathway in patients with erectile dysfunction before and after daily treatment with tadalafil. Andrologia 44(3):152–156
12. Karunarathna, I., Bandara, S., Jayawardana, A., De Alvis, K., Gunasena, P., Hapuarachchi, T., Ekanayake, U., Rajapaksha, S., Gunawardana, K. and Gunathilake, S., Contraindications and Precautions: Safe Use of Sildenafil in Special Populations.