Does aspirin make sildenafil more effective? This is a common question amongst men taking medication for erectile dysfunction, particularly those also prescribed aspirin for cardiovascular protection. Whilst both medications influence blood flow, they work through entirely different mechanisms. Sildenafil (Viagra) is a phosphodiesterase type 5 (PDE5) inhibitor that enhances erectile function by maintaining higher levels of cyclic guanosine monophosphate (cGMP) in penile tissue. Aspirin, conversely, is an antiplatelet agent that prevents blood clots. This article examines the evidence for any interaction between these medications, explores their safety when taken together, and provides guidance on when to seek professional medical advice.

How Sildenafil Works for Erectile Dysfunction

Sildenafil, commonly known by the brand name Viagra, is a phosphodiesterase type 5 (PDE5) inhibitor licensed for the treatment of erectile dysfunction (ED). The medication works by enhancing the natural erectile response to sexual stimulation rather than directly causing an erection.

When sexual arousal occurs, the body releases nitric oxide in the erectile tissue of the penis. This triggers an enzyme called guanylate cyclase, which increases levels of cyclic guanosine monophosphate (cGMP). The cGMP relaxes smooth muscle cells in the blood vessels of the penis, allowing increased blood flow into the corpora cavernosa—the spongy tissue that becomes engorged during an erection. Sildenafil works by inhibiting the PDE5 enzyme, which normally breaks down cGMP. By blocking this breakdown, sildenafil helps maintain higher levels of cGMP, prolonging smooth muscle relaxation and supporting the erectile response.

Key points about sildenafil's mechanism:

• Requires sexual stimulation to be effective—it does not cause spontaneous erections

• Typically begins working within 30–60 minutes of oral administration (high-fat meals may delay onset and reduce effect)

• Effects last approximately 4–6 hours, though this varies between individuals

• Available in 25mg, 50mg, and 100mg tablets, with 50mg being the usual starting dose

• Should not be taken more than once in 24 hours

It is important to understand that sildenafil treats the symptoms of erectile dysfunction but does not address underlying causes, which may include cardiovascular disease, diabetes, psychological factors, or hormonal imbalances. NICE Clinical Knowledge Summary guidance recommends that men with ED should receive appropriate assessment to identify and manage any underlying conditions alongside symptomatic treatment.

Does Aspirin Make Sildenafil More Effective?

There is no robust evidence or UK guideline recommendation that aspirin makes sildenafil more effective for treating erectile dysfunction. This is a common question, likely arising from the fact that both medications affect blood flow, but they work through entirely different mechanisms and target different aspects of vascular function.

Aspirin is an antiplatelet agent that works by irreversibly inhibiting the cyclooxygenase-1 (COX-1) enzyme in platelets, reducing the production of thromboxane A2. This makes platelets less likely to clump together, thereby reducing the risk of blood clots. Low-dose aspirin (typically 75mg daily) is primarily used for secondary prevention in people who have already experienced a cardiovascular event such as heart attack or stroke. In the UK, aspirin is not routinely recommended for primary prevention due to bleeding risks. Whilst aspirin does influence blood flow by preventing clot formation, this antiplatelet effect does not enhance the specific vasodilatory mechanism by which sildenafil works.

Some men taking both medications may have cardiovascular disease, which is itself a common cause of erectile dysfunction due to impaired blood vessel function. In these cases, any perceived improvement might relate to better overall cardiovascular health management rather than a direct interaction between the two drugs. Research has not demonstrated that aspirin enhances sildenafil's efficacy, and it is not recommended as an adjunct therapy for erectile dysfunction.

Important considerations:

• Aspirin should only be taken if prescribed or recommended by a healthcare professional

• Taking aspirin without medical advice can increase bleeding risk

• Any medication changes should be discussed with your GP

If sildenafil is not providing adequate results, there are alternative approaches including dose adjustment, trying different PDE5 inhibitors, or addressing underlying health conditions, which should be explored with your doctor rather than self-medicating with additional drugs.

Potential Interactions Between Aspirin and Sildenafil

Aspirin and sildenafil can generally be taken together safely. According to the sildenafil Summary of Product Characteristics (SmPC), sildenafil does not have a clinically meaningful effect on bleeding time, including when administered with aspirin. The bleeding risk associated with this combination is primarily driven by aspirin itself and any other anticoagulants or antiplatelets you may be taking.

Both medications can affect cardiovascular function, though through different mechanisms. Aspirin inhibits platelet aggregation, making blood less likely to clot, whilst sildenafil causes mild vasodilation and can lower blood pressure by approximately 8/5 mmHg on average. In most people taking low-dose aspirin for cardiovascular protection, this blood pressure reduction is not problematic.

Important contraindications for sildenafil include:

• Concurrent use of nitrate medications (such as glyceryl trinitrate for angina) due to the risk of severe hypotension

• Concurrent use of guanylate cyclase stimulators such as riociguat

Sildenafil should be used with caution in patients with certain cardiovascular conditions where sexual activity may be inadvisable, including recent heart attack or stroke (within 6 months), unstable angina, or severe heart failure. These are not absolute contraindications, but require careful assessment by a healthcare professional.

Interactions with alpha-blockers (medications for prostate enlargement or high blood pressure) can also occur. Patients should be stable on alpha-blocker therapy before starting sildenafil, begin with the lowest dose (25mg), and consider spacing the medications.

Practical advice:

• Always inform your doctor and pharmacist of all medications you are taking, including over-the-counter aspirin

• Report any unusual bleeding or bruising

• Do not adjust doses of either medication without medical advice

• Ensure your cardiovascular health has been properly assessed before starting sildenafil

Safety Considerations When Taking Both Medications

When taking aspirin and sildenafil together, several safety considerations should be observed to minimise risks and ensure appropriate use of both medications.

Bleeding risk management is important, particularly with aspirin. Patients should be vigilant for signs of increased bleeding, including:

• Prolonged bleeding from minor cuts

• Unexplained bruising or purpura (small purple spots on the skin)

• Blood in urine or stools (which may appear black and tarry)

• Nosebleeds that are difficult to stop

• Bleeding gums when brushing teeth

If any of these occur, contact your GP promptly. In cases of severe bleeding, call 999 or go to A&E immediately.

Cardiovascular monitoring is essential, particularly for men with existing heart disease. Sildenafil should not be used by anyone taking nitrate medications (such as glyceryl trinitrate for angina) or riociguat due to the risk of severe hypotension. The combination of sildenafil with aspirin does not create this same contraindication, but men with cardiovascular disease should have regular reviews with their GP to ensure their condition remains stable.

Gastrointestinal considerations are relevant for both medications. Aspirin can irritate the stomach lining and increase the risk of peptic ulcers and gastrointestinal bleeding. Sildenafil commonly causes dyspepsia (indigestion) as a side effect. Patients at higher risk of gastrointestinal complications (those over 65, with a history of ulcers, or taking other medications such as NSAIDs, steroids or anticoagulants) may be prescribed a proton pump inhibitor (PPI) such as omeprazole for gastric protection.

Medication adherence and timing:

• Take aspirin at the same time each day, usually with or after food

• Sildenafil should be taken approximately one hour before sexual activity, preferably on an empty stomach

• Do not exceed the prescribed dose of either medication

• Avoid alcohol excess, which can impair erectile function and increase bleeding risk

Patients should maintain an up-to-date list of all medications, including over-the-counter products and supplements, and share this with all healthcare providers. If you experience any suspected side effects, report them to the MHRA Yellow Card Scheme.

When to Speak with Your GP or Pharmacist

There are several circumstances when you should seek professional medical advice regarding the use of aspirin and sildenafil, either individually or in combination.

Before starting either medication, consultation is essential if you:

• Have a history of cardiovascular disease, including angina, heart attack, stroke, or heart failure

• Have uncontrolled high blood pressure or very low blood pressure

• Have a history of stomach ulcers or gastrointestinal bleeding

• Have liver or kidney impairment

• Have bleeding disorders or are taking anticoagulants (such as warfarin, rivaroxaban, or apixaban)

• Have retinal disorders or a history of non-arteritic anterior ischaemic optic neuropathy (NAION)

• Are taking nitrates, riociguat (absolute contraindications), alpha-blockers, or other blood pressure medications

• Are taking medications that inhibit CYP3A4 (e.g., erythromycin, clarithromycin, ketoconazole, itraconazole, or HIV protease inhibitors), which may require sildenafil dose adjustment

During treatment, contact your GP or pharmacist if:

• Sildenafil is not effective at the prescribed dose—do not increase the dose yourself

• You experience side effects from either medication, including headache, flushing, indigestion, visual disturbances, or dizziness

• You notice signs of increased bleeding as described in the previous section

• You develop chest pain during sexual activity—stop immediately and seek urgent medical attention

• You experience an erection lasting longer than 2 hours—this is a medical emergency requiring immediate treatment; call 999 or go to A&E

• You experience sudden vision or hearing loss—seek immediate medical attention

Pharmacy consultations can be valuable for:

• Checking for interactions with new medications or supplements

• Advice on timing and administration of medications

• Minor side effect management

• Understanding when GP review is necessary

Your community pharmacist is an accessible healthcare professional who can provide confidential advice about both prescription and over-the-counter medications. Many pharmacies now offer private consultation rooms for sensitive discussions.

Regular medication reviews with your GP are recommended, particularly if you have multiple health conditions or take several medications. NICE guidance suggests that men with erectile dysfunction should have underlying causes investigated and managed, which may improve erectile function and reduce the need for medication. Addressing cardiovascular risk factors, optimising diabetes control, reviewing medications that may contribute to ED, and considering psychological factors are all important aspects of comprehensive care that extend beyond simply prescribing sildenafil.

Frequently Asked Questions