Sildenafil and Paxlovid: Can You Take Them Together?

Sildenafil and Paxlovid: Understanding the Interaction

Published: 16 October 2026

If you're taking Paxlovid for COVID-19 and wondering about sildenafil and Paxlovid together, it's important to know that they can interact. Paxlovid contains ritonavir, a potent enzyme blocker that raises sildenafil levels in your blood, increasing the risk of side effects. However, sildenafil can still be used with careful dose adjustment and prescriber oversight—you should never take your usual dose without medical advice during a course of Paxlovid.

What is sildenafil and what is Paxlovid?

Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor used to treat erectile dysfunction (ED). It works by relaxing blood vessels in the penis, allowing increased blood flow when you're sexually aroused. Sildenafil is the active ingredient in Viagra and is available in 25mg, 50mg, and 100mg tablets, typically taken about one hour before sexual activity [3].

Paxlovid is an antiviral medicine used to treat COVID-19 in people at higher risk of severe illness. It contains two active ingredients: nirmatrelvir (which stops the virus replicating) and ritonavir (which boosts nirmatrelvir levels by blocking the liver enzyme CYP3A4 that would otherwise break it down). A course of Paxlovid usually lasts five days [12].

Because ritonavir is a potent CYP3A4 inhibitor, it doesn't just boost nirmatrelvir—it also slows the breakdown of many other medicines, including sildenafil. This means sildenafil stays in your body longer and reaches higher concentrations than usual, which is why the interaction between sildenafil and Paxlovid requires careful management.

How do sildenafil and Paxlovid interact?

The interaction occurs because ritonavir in Paxlovid is a potent inhibitor of the liver enzyme CYP3A4. Sildenafil is normally broken down by CYP3A4, so when this enzyme is blocked, sildenafil levels in the blood can rise significantly—sometimes several times higher than usual [3].

Higher sildenafil levels increase the risk and severity of side effects such as headache, flushing, dizziness, visual disturbances, and a drop in blood pressure. In rare cases, very high levels could lead to more serious problems like priapism (a painful erection lasting more than four hours) or cardiovascular effects, particularly in people with existing heart conditions.

This doesn't mean you cannot use sildenafil while taking Paxlovid, but it does mean the dose must be reduced and the timing carefully considered. The British National Formulary notes that when sildenafil is used with potent CYP3A4 inhibitors, a lower starting dose is required and the maximum dose may need to be reduced [3]. Your prescriber will assess your individual circumstances, including how long you've been on Paxlovid and whether you have other health conditions or take other medicines.

Why enzyme inhibition matters

CYP3A4 is one of the main enzymes responsible for metabolising (breaking down) medicines in the liver. When ritonavir blocks this enzyme, medicines that rely on CYP3A4 for clearance accumulate in the bloodstream. The effect is dose-dependent: the more ritonavir present, the greater the inhibition. Because Paxlovid is only taken for five days, the interaction is temporary, but it's at its strongest while you're actively taking the antiviral and for a few days afterwards as ritonavir clears from your system.

What your prescriber will check before combining sildenafil and Paxlovid

Before prescribing sildenafil to someone taking Paxlovid, or before advising on continuing sildenafil during a Paxlovid course, a UK prescriber will review several important factors. They will confirm the exact dose and duration of your Paxlovid treatment, check all your current medicines (including over-the-counter products and supplements), and assess your cardiovascular health, as both medicines can affect blood pressure [2][3].

The prescriber will also review any history of side effects from sildenafil, check for contraindications such as recent heart attack or stroke, use of nitrates or nicorandil, and ensure you're not taking another PDE5 inhibitor at the same time. If you take alpha-blockers (for prostate symptoms or high blood pressure), extra caution is needed because the combination with sildenafil can cause dizziness or fainting, and adding Paxlovid into the mix increases sildenafil levels further.

Your prescriber may recommend waiting until after your Paxlovid course is finished, or they may adjust your sildenafil dose significantly—often to 25mg or even lower—and advise taking it no more than once every 48 hours while on Paxlovid. They will also discuss warning signs to watch for and when to seek urgent help. At Cured Pharmacy, every prescription for sildenafil follows an online consultation reviewed by a UK-registered prescriber, ensuring all interactions and individual factors are considered.

Practical advice if you need both medicines

If you're prescribed Paxlovid and you currently use sildenafil, contact your prescriber or pharmacist before taking your next sildenafil dose. Do not assume your usual dose is safe—the interaction can be significant, and taking a full dose could lead to unpleasant or even dangerous side effects.

In many cases, the safest approach is to pause sildenafil for the five days you're taking Paxlovid and for two to three days afterwards, allowing ritonavir to clear from your system. If sexual activity is important during this period and your prescriber agrees it's safe, they may suggest a much lower dose of sildenafil (such as 25mg) taken no more than once every 48 hours, rather than the usual once-daily maximum.

Avoid grapefruit juice while taking either medicine, as it can also raise sildenafil levels. Limit alcohol, which can worsen erectile dysfunction and add to the blood-pressure-lowering effects of sildenafil. If you experience severe headache, dizziness, chest pain, visual changes, or an erection lasting more than four hours, seek medical help immediately. Never take sildenafil with nitrates, nicorandil, riociguat, poppers, or another PDE5 inhibitor, regardless of whether you're on Paxlovid—these combinations can cause a dangerous drop in blood pressure.

What about other ED medicines?

Other PDE5 inhibitors are also affected by Paxlovid. Tadalafil (Cialis) requires dose reduction—the maximum recommended dose is 10mg in 72 hours when used with potent CYP3A4 inhibitors [4]. Vardenafil (Levitra) and avanafil (Spedra) are contraindicated or should be avoided with potent CYP3A4 inhibitors like ritonavir [5][6]. Your prescriber will choose the safest option based on your individual circumstances, and in many cases waiting until after the Paxlovid course is the most straightforward approach.

Are there alternatives during a Paxlovid course?

If you need treatment for erectile dysfunction while taking Paxlovid and your prescriber advises against using sildenafil or other oral PDE5 inhibitors, there are a few alternatives to consider, though each has its own considerations.

Eroxon is a topical gel medical device that works locally rather than systemically, so it's not affected by the CYP3A4 interaction with Paxlovid. It's applied directly to the head of the penis and can work within 10 minutes. Because it doesn't enter the bloodstream in significant amounts, it doesn't interact with ritonavir. However, it may not be as effective as oral PDE5 inhibitors for some men.

Prescription-only options such as Vitaros (alprostadil cream) or Caverject (alprostadil injection) are also not metabolised by CYP3A4 and therefore don't interact with Paxlovid in the same way [7]. These require careful instruction and are usually considered when oral treatments are unsuitable. Your prescriber can discuss whether these are appropriate for you, though for a short five-day course of Paxlovid, many men find it simpler to wait until the antiviral treatment is finished before resuming their usual ED medication.

When to seek medical advice about sildenafil and Paxlovid

You should contact a healthcare professional before taking sildenafil if you've been prescribed Paxlovid, or if you're prescribed Paxlovid while already using sildenafil. Do not adjust doses yourself—the prescriber needs to review your full medication list and health history to make a safe decision.

Seek urgent medical help (call 999 or go to A&E) if you experience chest pain during or after sexual activity, an erection lasting more than four hours, sudden loss of vision or hearing, or severe dizziness or fainting. These are rare but serious side effects that require immediate attention.

If you develop new or worsening erectile dysfunction, it's important to see your GP even if you're managing it with over-the-counter or online treatments. ED can be an early warning sign of cardiovascular disease or diabetes, and addressing the underlying cause is just as important as treating the symptom [1][2]. At Cured Pharmacy, our online consultation process is designed to identify when you should see your GP for further investigation, and we encourage you to do so if our prescribers recommend it.

Ongoing monitoring and follow-up

If you regularly use sildenafil and you've had to adjust or pause treatment because of a Paxlovid course, follow up with your prescriber once the antiviral is finished. They can confirm when it's safe to return to your usual dose—typically two to three days after the last Paxlovid dose, once ritonavir has cleared. Keep a record of any side effects or concerns during the interaction period, as this information helps your prescriber tailor future treatment if you need another course of Paxlovid or a similar medicine.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 16 October 2026]
2. National Institute for Health and Care Excellence. (n.d.). Erectile dysfunction. Clinical Knowledge Summaries. https://cks.nice.org.uk/topics/erectile-dysfunction/ [accessed 16 October 2026]
3. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 16 October 2026]
4. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 16 October 2026]
5. Joint Formulary Committee. (n.d.). Vardenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/vardenafil/ [accessed 16 October 2026]
6. Joint Formulary Committee. (n.d.). Avanafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/avanafil/ [accessed 16 October 2026]
7. Joint Formulary Committee. (n.d.). Alprostadil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/alprostadil/ [accessed 16 October 2026]
8. Electronic Medicines Compendium. (n.d.). Summaries of Product Characteristics and Patient Information Leaflets. https://www.medicines.org.uk/emc/ [accessed 16 October 2026]

Information on this page is for educational purposes only and is not medical advice. Prescription treatments require clinical assessment by a UK-registered prescriber. Always consult a qualified healthcare professional before starting or changing any medication.

Get Treatment in 3 Steps

1

Choose your treatment

Select from our recommended UK-licensed medications.

2

Answer quick questions

Select safe UK treatments. Quick answers.

3

Get it delivered fast

We will deliver direct to you as quickly as tomorrow.