Sildenafil and Fluoxetine: Can You Take Them Together?

Sildenafil and Fluoxetine: Understanding the Interaction

Published: 16 October 2026

Many men wonder whether sildenafil and fluoxetine can be taken together safely. The good news is that these two medicines do not have a major, dangerous interaction and are often prescribed together [3]. However, there are important considerations your prescriber will check to ensure the combination is right for you, particularly because fluoxetine can sometimes contribute to erectile difficulties as a side effect.

What is sildenafil and fluoxetine used for?

Sildenafil is a medicine used to treat erectile dysfunction (ED) in men. It belongs to a group of medicines called PDE5 inhibitors, which work by relaxing blood vessels in the penis, allowing more blood to flow in when you are sexually aroused [1][3]. Sildenafil is the active ingredient in Viagra and is also available as a generic medicine. It is usually taken about one hour before sexual activity, and you should not take it more than once a day [3].

Fluoxetine is an antidepressant that belongs to a class of medicines called selective serotonin reuptake inhibitors (SSRIs). It is commonly prescribed to treat depression, obsessive-compulsive disorder (OCD), bulimia nervosa, and panic disorder. Fluoxetine works by increasing levels of serotonin, a chemical messenger in the brain that helps regulate mood. While effective for mental health conditions, SSRIs like fluoxetine can sometimes cause sexual side effects, including difficulty achieving or maintaining an erection [12].

Can you take sildenafil and fluoxetine together?

Yes, sildenafil and fluoxetine can generally be taken together, and this combination is commonly prescribed in the UK [3]. There is no major, dangerous interaction between these two medicines that would make the combination unsafe. In fact, sildenafil is sometimes used to help manage erectile difficulties that can occur as a side effect of fluoxetine and other SSRI antidepressants.

However, it is essential that your prescriber knows about all the medicines you are taking, including fluoxetine, before prescribing sildenafil. During your consultation, the prescriber will review your full medical history and current medications to ensure sildenafil is suitable for you. They will check for any other medicines or health conditions that might affect how sildenafil works or increase the risk of side effects. Never start or stop any prescribed medicine, including fluoxetine, without speaking to your doctor or pharmacist first.

Why fluoxetine may cause erectile difficulties

Sexual side effects, including erectile dysfunction, reduced libido, and delayed ejaculation, are well-recognised effects of SSRI antidepressants like fluoxetine [12]. These effects occur because serotonin plays a complex role in sexual function, and increasing serotonin levels can sometimes interfere with the sexual response cycle. If you experience erectile difficulties while taking fluoxetine, it is important to discuss this with your GP rather than stopping the antidepressant on your own, as your doctor may be able to adjust your treatment or prescribe an ED medicine like sildenafil to help.

How do sildenafil and fluoxetine interact in the body?

Sildenafil and fluoxetine do not interact in a way that causes a dangerous change in how either medicine works. Fluoxetine is broken down in the liver by enzymes, including one called CYP3A4, and it can also inhibit other liver enzymes. Sildenafil is also metabolised by CYP3A4 [3]. In theory, fluoxetine could slightly increase the levels of sildenafil in the blood, but this effect is generally mild and not considered clinically significant at usual doses.

The main consideration when taking these medicines together is not a direct drug interaction, but rather the overall picture of your health and other medications. Your prescriber will ensure that sildenafil is safe for you by checking for contraindicated medicines (such as nitrates, nicorandil, riociguat, or poppers) and assessing your cardiovascular health [2][3]. Both medicines can, in rare cases, affect blood pressure, so your prescriber will take this into account, especially if you are also taking other blood-pressure-lowering medicines.

What does your prescriber check before prescribing sildenafil and fluoxetine?

Before prescribing sildenafil to someone taking fluoxetine, a UK prescriber will carry out a thorough consultation to ensure the combination is safe and appropriate [2]. They will ask about your current medicines, including the dose of fluoxetine you are taking and how long you have been on it. They will also ask about any other antidepressants or mental health medicines, as well as any other prescription or over-the-counter medicines, herbal remedies, or supplements.

The prescriber will check for any medicines that must not be taken with sildenafil, such as nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, or amyl/alkyl nitrites (poppers) [3]. Taking sildenafil with any of these can cause a dangerous drop in blood pressure. They will also ask about your cardiovascular health, including any history of heart attack, stroke, angina, heart failure, or very low blood pressure, as sildenafil may not be suitable if sexual activity is inadvisable [2][3].

Your prescriber will also consider whether you are taking any other medicines that can interact with sildenafil, such as alpha-blockers (e.g. tamsulosin, doxazosin) or potent CYP3A4 inhibitors (e.g. ritonavir, ketoconazole, clarithromycin), which may require a lower starting dose of sildenafil or extra caution [3]. The consultation is an opportunity to discuss any concerns and ensure the treatment plan is tailored to your individual needs.

Declaring all your medicines

It is vital to list every medicine you take during your consultation, including fluoxetine and any other antidepressants, blood pressure medicines, medicines for prostate problems, HIV medicines, antifungals, antibiotics, and any over-the-counter or herbal products. Even if you think a medicine is unrelated to ED, it may still be relevant to your prescriber's safety checks. Do not stop taking fluoxetine or any other prescribed medicine without advice from your GP, as stopping antidepressants suddenly can cause withdrawal symptoms.

Practical advice for taking sildenafil and fluoxetine together

If you are prescribed sildenafil while taking fluoxetine, take each medicine exactly as directed. Sildenafil is usually taken about one hour before you plan to have sex, and it works only when you are sexually aroused [3]. You should not take sildenafil more than once in 24 hours. Continue taking your fluoxetine as prescribed by your doctor; do not skip doses or stop taking it without medical advice.

Be aware of potential side effects from both medicines. Common side effects of sildenafil include headache, flushing, indigestion, and nasal congestion [3]. Fluoxetine can cause nausea, headache, sleep disturbances, and, as mentioned, sexual side effects [12]. If you experience any new or worsening symptoms after starting sildenafil, contact your prescriber or pharmacist for advice.

Avoid drinking large amounts of alcohol, as heavy drinking can worsen erectile difficulties and add to the blood-pressure-lowering effects of sildenafil, increasing the risk of dizziness or fainting [3]. Grapefruit juice can increase sildenafil levels in the blood, so it is best to avoid it. If you are prescribed any new medicines by your GP or another healthcare professional, always tell them you are taking both sildenafil and fluoxetine.

When to seek urgent help with sildenafil and fluoxetine

While sildenafil and fluoxetine are generally safe to take together, there are some warning signs that require urgent medical attention. If you develop an erection that lasts longer than four hours (priapism), seek emergency help immediately, as this can cause permanent damage if not treated promptly [3]. Call 999 or go to A&E.

Seek urgent help if you experience sudden loss of vision in one or both eyes, or sudden decrease or loss of hearing, which may be accompanied by ringing in the ears or dizziness [3]. These are rare but serious side effects of sildenafil. If you develop chest pain during or after sexual activity, stop and seek medical help straight away; do not take nitrate medicines (such as GTN spray) if you have used sildenafil in the past 24 hours, as this combination can be dangerous [3].

If you experience severe dizziness, fainting, or signs of a severe allergic reaction (such as swelling of the face, lips, or throat, or difficulty breathing), call 999. If you have concerns about side effects from fluoxetine, such as worsening depression, suicidal thoughts, or unusual mood changes, contact your GP or mental health team urgently. You can also call NHS 111 for advice if you are unsure whether your symptoms need urgent attention.

Reporting side effects

If you experience any side effects from sildenafil or fluoxetine, you can report them via the Yellow Card Scheme at https://yellowcard.mhra.gov.uk/ or by searching for 'Yellow Card' in the Google Play or Apple App Store. Reporting side effects helps improve the safety information available for these medicines.

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. 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.