Sildenafil and Cannabis: Is It Safe to Use Together?

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At a glance

What is sildenafil and how does it work?

Sildenafil is a prescription medicine used to treat erectile dysfunction (ED) in men. It belongs to a group of medicines called phosphodiesterase type 5 (PDE5) inhibitors. Sildenafil works by relaxing the blood vessels in the penis, allowing more blood to flow into the area when you are sexually aroused. This helps you get and maintain an erection suitable for sexual activity [3].

Sildenafil is available in doses of 25mg, 50mg, and 100mg. You usually take it about one hour before sex, and it can remain effective for up to four hours. Sexual stimulation is still needed for the medicine to work—sildenafil will not cause an erection on its own [1][3].

Sildenafil is the active ingredient in branded Viagra, but it is also available as a lower-cost generic medicine. At Cured Pharmacy, sildenafil is supplied after an online consultation reviewed by a UK-registered prescriber to ensure it is safe and suitable for you.

What is cannabis and how does it affect the body?

Cannabis (also known as marijuana or weed) is a plant-based substance that contains active compounds called cannabinoids, the most well-known being THC (tetrahydrocannabinol) and CBD (cannabidiol). THC is the psychoactive component responsible for the 'high' associated with cannabis use. Cannabis can be smoked, vaped, or consumed in edible form.

Cannabis affects the cardiovascular system in several ways. It can cause an initial increase in heart rate, followed by a drop in blood pressure, particularly when standing up (orthostatic hypotension). This can lead to dizziness, light-headedness, or even fainting in some people. The effects vary depending on the dose, method of use, and individual tolerance.

In the UK, cannabis is a controlled substance under the Misuse of Drugs Act 1971, and recreational use is illegal. However, some people use it for various reasons, and it is important to be honest with your prescriber about any cannabis use so they can assess your suitability for sildenafil safely.

Cannabis and erectile function

The relationship between cannabis and erectile function is complex. Some users report that cannabis enhances sexual pleasure or reduces performance anxiety, while others find that regular or heavy use can contribute to erectile difficulties. Chronic cannabis use may affect hormone levels and blood flow, potentially worsening ED over time [10]. If you are experiencing ED, it is worth discussing your cannabis use openly with a healthcare professional.

Do sildenafil and cannabis interact with each other?

There is no direct pharmacological interaction between sildenafil and cannabis that makes the combination absolutely contraindicated. However, both substances can lower blood pressure, and using them together may add to this effect. Sildenafil works by dilating blood vessels, which can cause a modest drop in blood pressure. Cannabis can also lower blood pressure, especially when changing position from sitting or lying to standing [3].

When sildenafil and cannabis are used together, the combined blood-pressure-lowering effect may increase the risk of dizziness, light-headedness, fainting, or a rapid heartbeat. This is particularly important if you are also taking other medicines that affect blood pressure, such as alpha-blockers or antihypertensives. The risk is higher if you use a large amount of cannabis or if you are not accustomed to either substance.

No major clinical studies have specifically examined the interaction between sildenafil and cannabis in detail, so the evidence is limited. However, the potential for additive cardiovascular effects means that caution is advised. Your prescriber will ask about your cannabis use during the consultation to assess whether sildenafil is safe for you and to provide tailored advice.

What you need to know

• Sildenafil and cannabis are not absolutely contraindicated, but both can lower blood pressure.
• Combining them may increase the risk of dizziness, light-headedness, or fainting.
• Always tell your prescriber about cannabis use so they can assess your suitability for sildenafil.
• Avoid large amounts of cannabis and be cautious when standing up after taking sildenafil.
• Seek urgent help for chest pain, erection lasting over four hours, or sudden vision or hearing loss.

What does your prescriber check before prescribing sildenafil?

Before prescribing sildenafil, your prescriber will review your full medical history, including any current medicines, recreational drug use (including cannabis), and underlying health conditions. They will check for contraindications—conditions or medicines that make sildenafil unsafe. For example, sildenafil must never be taken with nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, or alkyl nitrites (poppers), as this combination can cause a dangerous drop in blood pressure [3].

Your prescriber will also ask about cardiovascular health, including blood pressure, history of heart attack or stroke, angina, and heart failure. Sildenafil is not suitable if sexual activity is inadvisable due to severe heart disease or very low blood pressure. They will review any medicines that might interact with sildenafil, such as alpha-blockers (e.g. tamsulosin, doxazosin) or potent CYP3A4 inhibitors (e.g. ritonavir, ketoconazole), and adjust the dose if necessary [2][3].

You should be honest about your cannabis use, including how often and how much you use. This information is confidential and helps your prescriber assess your suitability for sildenafil and advise you on how to minimise risks. If you are using cannabis regularly or have any concerns about blood pressure or dizziness, your prescriber may recommend starting on a lower dose of sildenafil or suggest alternative approaches.

Medicines that must not be taken with sildenafil

Do not take sildenafil together with nitrates (GTN spray, isosorbide mononitrate, isosorbide dinitrate), nicorandil, riociguat, alkyl nitrites (poppers), or another PDE5 inhibitor (such as tadalafil, vardenafil, or avanafil). Combining sildenafil with any of these can cause a severe and potentially life-threatening drop in blood pressure [3]. Always tell your prescriber about every medicine you take, including over-the-counter products and recreational substances.

Practical advice for using sildenafil and cannabis safely

If you choose to use cannabis and your prescriber has deemed sildenafil safe for you, there are steps you can take to reduce the risk of side effects. Avoid using large amounts of cannabis around the time you take sildenafil, as this increases the chance of dizziness or fainting. Be cautious when standing up from a sitting or lying position, especially in the first few hours after taking sildenafil or using cannabis.

Limit alcohol intake, as heavy drinking can worsen erectile dysfunction and add to the blood-pressure-lowering effects of both sildenafil and cannabis. Stay well hydrated, and avoid taking sildenafil on an empty stomach if you are prone to dizziness. If you experience significant dizziness, light-headedness, or a rapid heartbeat, sit or lie down until the symptoms pass, and seek medical advice if they persist or worsen.

If you are new to sildenafil, your prescriber may recommend starting with a lower dose (such as 25mg or 50mg) to see how you respond. Do not exceed the recommended dose, and do not take sildenafil more than once in 24 hours. If you have any concerns about using sildenafil alongside cannabis, discuss them with your prescriber or pharmacist before taking the medicine.

When to get urgent help

• Chest pain during or after sexual activity—call 999 immediately and tell them you have taken sildenafil.
• An erection lasting longer than 4 hours (priapism)—go to A&E straight away to prevent permanent damage.
• Sudden loss of vision in one or both eyes, or sudden decrease or loss of hearing—seek emergency medical attention.
• Severe dizziness, fainting, or very rapid or irregular heartbeat—contact NHS 111 or your GP urgently.
• Never take nitrate medicines (GTN spray, isosorbide) if you have used sildenafil in the past 24 hours.

Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.

When to seek urgent medical help

While serious side effects from sildenafil are uncommon, you should seek urgent medical help in certain situations. If you develop chest pain during or after sexual activity, stop and call 999 or go to A&E immediately. Do not take nitrate medicines (such as GTN spray) if you have used sildenafil in the past 24 hours, as this can cause a dangerous drop in blood pressure. Tell the paramedics or emergency doctor that you have taken sildenafil [3].

If you have an erection that lasts longer than four hours (priapism), seek emergency medical attention. Priapism can damage the penis if not treated promptly. Sudden loss of vision in one or both eyes, or sudden decrease or loss of hearing (sometimes with ringing in the ears or dizziness), are rare but serious side effects that require immediate medical assessment [3].

If you experience severe dizziness, fainting, or a very rapid or irregular heartbeat after taking sildenafil, especially if you have also used cannabis or alcohol, seek medical advice promptly. If you are unsure whether your symptoms are serious, contact NHS 111 for guidance or speak to your GP or pharmacist.

Alternatives to sildenafil for erectile dysfunction

If sildenafil is not suitable for you, or if you experience troublesome side effects, other PDE5 inhibitors may be an option. Tadalafil (Cialis) has a longer duration of action (up to 36 hours) and can also be taken daily at a lower dose. Vardenafil (Levitra) and avanafil (Spedra) are alternatives with different onset times and durations. Your prescriber can discuss which option is best for your circumstances [2][4][5][6]. All prescription ED medicines at Cured Pharmacy are supplied after a consultation reviewed by a UK-registered prescriber.