Tadalafil and Oseltamivir: Can You Take Them Together?

Takes less than 2 minutes to complete 100% online

Key takeaways

• No major interaction between tadalafil and oseltamivir is commonly reported
• Always declare all medicines during your consultation for a full safety check
• Never take tadalafil with nitrates, nicorandil, riociguat, or poppers
• Consider your overall health and energy levels when unwell with flu
• Tadalafil requires a prescription after review by a UK-registered prescriber

What Is Tadalafil and How Does It Work?

Tadalafil is a prescription medicine licensed in the UK for the treatment of erectile dysfunction (ED). It belongs to a class of medicines called phosphodiesterase type 5 (PDE5) inhibitors, which work by relaxing the blood vessels in the penis, allowing increased blood flow when you are sexually aroused [3][4].

Tadalafil is available in two forms: on-demand tablets (usually 10mg or 20mg) taken at least 30 minutes before sexual activity, with effects lasting up to 36 hours, and daily low-dose tablets (2.5mg or 5mg) for continuous treatment. Both require sexual stimulation to work—tadalafil does not cause an erection on its own [4].

The medicine is sold under the brand name Cialis, but generic versions are widely available and equally effective. At Cured Pharmacy, tadalafil is available after an online consultation reviewed by a UK-registered prescriber, who will check that it is safe and suitable for you.

What Is Oseltamivir and When Is It Used?

Oseltamivir, marketed as Tamiflu, is an antiviral medicine used to treat and prevent influenza (flu). It works by blocking the action of neuraminidase, an enzyme that the flu virus needs to spread from infected cells to healthy ones. By inhibiting this enzyme, oseltamivir can reduce the severity and duration of flu symptoms if started within 48 hours of symptom onset.

Oseltamivir is typically prescribed during flu season or during outbreaks, particularly for people at higher risk of complications from influenza, such as those with chronic health conditions, older adults, or pregnant women. It is usually taken twice daily for five days when treating active flu, or once daily when used for prevention.

Because oseltamivir is an antiviral and tadalafil is a PDE5 inhibitor, they work on completely different systems in the body. This means they do not share the same metabolic pathways or mechanisms of action, which reduces the likelihood of a direct drug interaction.

At a glance

The Interaction Between Tadalafil and Oseltamivir

No significant interaction between tadalafil and oseltamivir is commonly reported in clinical practice or major drug interaction databases. These medicines work through entirely different mechanisms: tadalafil affects blood flow to the penis by inhibiting PDE5, while oseltamivir targets the influenza virus by blocking neuraminidase.

Tadalafil is primarily metabolised by the liver enzyme CYP3A4, and oseltamivir does not significantly inhibit or induce this enzyme. This means oseltamivir is unlikely to alter the levels of tadalafil in your bloodstream, and vice versa. However, it is important to remember that being unwell with flu can affect your overall health, energy levels, and desire for sexual activity.

During your online consultation at Cured Pharmacy, the prescriber will review all your current medicines, including any recent antiviral treatments, to ensure there are no contraindications or concerns specific to your health. While the combination of tadalafil and oseltamivir is not expected to cause problems, individual circumstances always matter.

How Your Body Processes These Medicines

Tadalafil is absorbed in the gut and broken down mainly by the liver enzyme CYP3A4, with a smaller contribution from CYP2C9. It has a long half-life of about 17.5 hours, which is why its effects can last up to 36 hours [4]. Oseltamivir, on the other hand, is converted in the liver to its active form (oseltamivir carboxylate) and is eliminated primarily by the kidneys. Because these pathways do not overlap significantly, the risk of one medicine interfering with the other is low.

What Your Prescriber Checks Before Approving Tadalafil

Even though tadalafil and oseltamivir are not known to interact significantly, your prescriber must still carry out a full clinical assessment before approving tadalafil. This includes reviewing your medical history, current medicines, and any recent illnesses or treatments [2].

The prescriber will specifically check for medicines that are contraindicated with tadalafil, such as nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, or recreational drugs known as 'poppers' (amyl or alkyl nitrites). Taking tadalafil with any of these can cause a dangerous drop in blood pressure and must be avoided [3][4].

They will also review medicines that can raise tadalafil levels, such as potent CYP3A4 inhibitors (for example, ritonavir, cobicistat, ketoconazole, itraconazole, or clarithromycin). If you are taking any of these, the prescriber may need to adjust your tadalafil dose or recommend an alternative. Alpha-blockers for prostate symptoms (such as tamsulosin or doxazosin) also require careful assessment, as they can add to the blood-pressure-lowering effect of tadalafil [4].

If you are currently taking oseltamivir for flu, simply declare this during your consultation. The prescriber will confirm that it does not pose a risk, but they will also consider whether you are well enough for sexual activity while recovering from influenza.

Practical Advice When Taking Tadalafil and Oseltamivir

If you have been prescribed oseltamivir for flu and you also use tadalafil for erectile dysfunction, there is no need to stop either medicine based solely on the combination. However, it is sensible to consider your overall health and energy levels. Flu can leave you feeling fatigued, feverish, and generally unwell, which may naturally reduce your interest in or ability to engage in sexual activity.

Take each medicine exactly as prescribed. Oseltamivir is usually taken twice daily with or without food, and it is important to complete the full course even if you start to feel better. Tadalafil on-demand tablets should be taken at least 30 minutes before sexual activity, and you should not take more than one dose in 24 hours [4].

Stay well hydrated, especially if you have flu symptoms such as fever or sweating. Dehydration can contribute to dizziness or low blood pressure, which may be more noticeable if you are also taking tadalafil. Avoid heavy alcohol while taking tadalafil, as this can increase the risk of side effects such as headache, dizziness, and low blood pressure, and can also worsen erectile dysfunction [3][4].

If you experience any unexpected symptoms or side effects while taking both medicines, contact your GP or pharmacist for advice. Do not stop a prescribed medicine without professional guidance.

When to Delay Sexual Activity

While tadalafil and oseltamivir can be taken together, it is worth considering whether sexual activity is advisable while you are unwell with flu. Influenza can place additional strain on your heart and lungs, and if you have underlying cardiovascular conditions, your GP may advise rest until you have fully recovered. Listen to your body and prioritise your overall health.

Other Medicines and Tadalafil: What You Need to Know

While oseltamivir does not interact significantly with tadalafil, many other medicines do require careful consideration. It is essential to declare all your current medicines, including over-the-counter treatments, herbal supplements, and recreational drugs, during your consultation [2][12].

Never take tadalafil with nitrates (used for angina), nicorandil, riociguat (for pulmonary hypertension), or poppers. This combination can cause a severe and potentially life-threatening drop in blood pressure [3][4]. If you are taking alpha-blockers such as tamsulosin or doxazosin for prostate symptoms, your prescriber will ensure you are stable on that medicine and will usually start you on the lowest dose of tadalafil.

Potent CYP3A4 inhibitors, including some HIV medicines (ritonavir, cobicistat), antifungals (ketoconazole, itraconazole), and antibiotics (clarithromycin), can increase tadalafil levels and may require dose adjustments. Conversely, CYP3A4 inducers such as rifampicin, carbamazepine, phenytoin, and St John's wort can reduce the effectiveness of tadalafil [4][12].

Grapefruit juice can also raise tadalafil levels and should be avoided. If you take other blood-pressure medicines, the prescriber will assess whether the combination is safe, as tadalafil can add to the blood-pressure-lowering effect. Always be honest and thorough when listing your medicines—your safety depends on it.

What to Do If You Start a New Medicine

If your GP or another healthcare professional prescribes a new medicine while you are taking tadalafil, always tell them you use ED treatment. Similarly, if you are prescribed a new medicine and you already have tadalafil at home, check with your pharmacist or prescriber before taking them together. Do not assume that because one combination is safe, all others will be.

When to get urgent help

• Erection lasting more than 4 hours (priapism)—go to A&E immediately
• Sudden loss of vision or hearing—stop tadalafil and seek urgent medical help
• Chest pain during or after sex—stop activity, call 999, and do not take more tadalafil
• Severe dizziness, fainting, or signs of very low blood pressure—seek same-day medical advice

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

Choose your treatment

Select from our recommended UK-licensed medications.

Answer quick questions

Select safe UK treatments. Quick answers.

Get it delivered fast

We will deliver direct to you as quickly as tomorrow.