Tadalafil and Biktarvy: Can They Be Taken Together?

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At a glance

What Is Tadalafil and How Does It Work?

Tadalafil is a prescription 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 increased blood flow when you are sexually aroused [3][4]. Unlike some other ED treatments, tadalafil has a long duration of action—its effects can last up to 36 hours, which is why it is sometimes called the 'weekend pill'.

Tadalafil is available in two forms: on-demand tablets (usually 10 mg or 20 mg taken at least 30 minutes before sexual activity) and daily low-dose tablets (2.5 mg or 5 mg taken once a day). Both require sexual stimulation to work; tadalafil does not cause an automatic erection [4]. The medicine is broken down in the liver by an enzyme called CYP3A4, and this is where the interaction with Biktarvy becomes important.

What Is Biktarvy and Why Does It Affect Tadalafil?

Biktarvy is a combination tablet used to treat HIV-1 infection. It contains three active ingredients: bictegravir, emtricitabine, and tenofovir alafenamide. Importantly, Biktarvy does not contain a 'boosting' agent like cobicistat or ritonavir, which are found in some other HIV regimens. This is a key point: Biktarvy itself is not a potent CYP3A4 inhibitor, so it does not significantly raise tadalafil levels in the same way that boosted regimens do [12].

However, some men may have previously been on a different HIV treatment that did contain cobicistat or ritonavir, or they may be taking other medicines that affect the same enzyme. For this reason, your prescriber will always review your complete medication list during the consultation. If you are taking Biktarvy alone (without additional boosters or potent CYP3A4 inhibitors), no dose adjustment of tadalafil is usually required, but your doctor or pharmacist will confirm this based on your individual circumstances [4][12].

The Role of CYP3A4 Inhibitors

CYP3A4 is a liver enzyme responsible for breaking down many medicines, including tadalafil. Potent CYP3A4 inhibitors—such as ritonavir, cobicistat (found in some HIV regimens like Genvoya or Stribild), ketoconazole, itraconazole, and clarithromycin—slow down this breakdown, causing tadalafil to stay in the body longer and reach higher levels [4]. This increases the risk of side effects such as headache, flushing, dizziness, or a drop in blood pressure. If you are taking a potent inhibitor alongside or instead of Biktarvy, your prescriber will recommend a reduced maximum dose of tadalafil (for example, 10 mg in 72 hours for on-demand use, or avoiding daily tadalafil altogether) [4][12].

Can You Take Tadalafil and Biktarvy Together?

Yes, tadalafil and Biktarvy can generally be taken together without major concerns, because Biktarvy on its own does not significantly inhibit the CYP3A4 enzyme [12]. This means that if you are taking Biktarvy as your only HIV medication (and no other potent CYP3A4 inhibitors), you can usually use the standard doses of tadalafil—10 mg or 20 mg on-demand, or 2.5 mg to 5 mg daily—as recommended by your prescriber [4].

That said, every person's medication list is different. Your prescriber will review all your current medicines during the online consultation to check for other interactions, including any additional antiretrovirals, antifungals, antibiotics, or blood-pressure medicines. It is essential to declare every medicine you take, including over-the-counter products and supplements, so that your treatment can be tailored safely. Never assume a combination is safe without a clinical check, even if Biktarvy alone does not require a dose change [2][4].

What you need to know

• Tadalafil and Biktarvy can usually be taken together without dose adjustment, as Biktarvy does not significantly inhibit CYP3A4.
• If you take other HIV medicines containing ritonavir or cobicistat, a lower tadalafil dose may be needed.
• Never take tadalafil with nitrates, nicorandil, riociguat, or poppers—this combination is dangerous.
• Your prescriber reviews all your medicines during the consultation to ensure tadalafil is safe for you.
• Erectile dysfunction can be an early sign of heart disease or diabetes—see your GP for a health check.

What Your Prescriber Checks Before Prescribing Tadalafil

When you request tadalafil through Cured Pharmacy, a UK-registered prescriber will review your online consultation answers carefully. They will check your full medication list to identify any potent CYP3A4 inhibitors (such as ritonavir, cobicistat, or certain antifungals) that might require a dose adjustment [4]. They will also ask about other medicines that can interact with tadalafil, including nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, alpha-blockers (such as doxazosin or tamsulosin), and other blood-pressure treatments [3][4].

Your prescriber will also assess your cardiovascular health. Tadalafil is not suitable if sexual activity is inadvisable—for example, if you have had a recent heart attack or stroke, unstable angina, severe heart failure, or very low blood pressure [4]. They will ask about any history of sudden vision loss (a rare condition called non-arteritic anterior ischaemic optic neuropathy, or NAION) or inherited retinal disorders, as these are contraindications to PDE5 inhibitors [3][4]. The consultation ensures that tadalafil is both safe and appropriate for you, taking into account your HIV treatment and overall health.

Alpha-Blockers and Blood Pressure

Some men with HIV may also take medicines for high blood pressure or an enlarged prostate, such as alpha-blockers (doxazosin, tamsulosin, alfuzosin). Combining these with tadalafil can increase the risk of dizziness or a sudden drop in blood pressure when standing up [3][4]. If you take an alpha-blocker, your prescriber will usually recommend starting tadalafil at the lowest dose and ensuring you are stable on the alpha-blocker first. Always mention these medicines in your consultation, even if you think they are unrelated to ED [2][4].

Practical Advice for Taking Tadalafil with Biktarvy

If your prescriber confirms that tadalafil is suitable for you, take it exactly as directed. For on-demand tadalafil (10 mg or 20 mg), take one tablet at least 30 minutes before you plan to have sex; the effect can last up to 36 hours, but you should not take more than one dose in 24 hours [4]. For daily tadalafil (2.5 mg or 5 mg), take one tablet at the same time each day, whether or not you plan to have sex. Sexual stimulation is still needed for the medicine to work [4].

Take Biktarvy as prescribed by your HIV specialist—usually one tablet once a day with or without food. There is no need to separate the timing of Biktarvy and tadalafil; you can take them at the same time or at different times of day, whichever suits your routine [12]. Avoid drinking large amounts of alcohol, as this can worsen erectile dysfunction and add to the blood-pressure-lowering effect of tadalafil, increasing the risk of dizziness [3][4]. Grapefruit juice can raise tadalafil levels and should be avoided or limited [4].

Common side effects of tadalafil include headache, indigestion, back pain, muscle aches, flushing, and a blocked or runny nose [4]. These are usually mild and short-lived. However, seek urgent medical help (call 999 or go to A&E) if you experience an erection lasting more than four hours (priapism), sudden loss of vision or hearing, or chest pain during sex [3][4]. If you feel dizzy or faint, sit or lie down until it passes, and mention it to your prescriber at your next review.

When to get urgent help

• Erection lasting more than 4 hours (priapism)—call 999 or go to A&E immediately
• Sudden loss of vision or hearing—seek urgent medical attention
• Chest pain during or after sex—stop activity, call 999, and do not take more tadalafil
• Severe dizziness or fainting, especially when standing—sit or lie down and contact your prescriber
• Allergic reaction (rash, swelling of face or throat, difficulty breathing)—call 999

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

Other Medicines and When to Seek Advice

In addition to Biktarvy, you may be taking other medicines for conditions such as high blood pressure, diabetes, or mental health. Most of these can be used alongside tadalafil, but some require caution. For example, other blood-pressure medicines (such as ACE inhibitors, calcium-channel blockers, or diuretics) can add to the blood-pressure-lowering effect of tadalafil, so your prescriber will check that your blood pressure is stable [2][4].

Never take tadalafil if you are using nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, or recreational drugs known as 'poppers' (amyl or alkyl nitrites). The combination can cause a dangerous drop in blood pressure [3][4]. Do not take tadalafil together with another PDE5 inhibitor (such as sildenafil, vardenafil, or avanafil) on the same day. If you are prescribed a new medicine by your GP or HIV specialist after starting tadalafil, check with your pharmacist or doctor whether it is safe to continue, especially if it is an antifungal, antibiotic, or another antiretroviral [4][12].

If you have any concerns about interactions, or if you experience unexpected side effects, contact your prescriber or pharmacist promptly. Do not stop taking Biktarvy or any other prescribed medicine without advice from your HIV specialist, as this could affect your viral load and overall health [12]. Cured Pharmacy's clinical team is available to answer questions and review your treatment at any time.

When to See Your GP

Erectile dysfunction can be an early warning sign of underlying health conditions, such as heart disease, diabetes, or high blood pressure [1][2]. If you are experiencing ED for the first time, it is a good idea to see your GP for a general health check, even if you are already under the care of an HIV specialist. Your GP can assess your cardiovascular risk, check your blood sugar and cholesterol, and discuss lifestyle factors such as smoking, alcohol, exercise, and stress [1][2]. Treating the underlying cause—alongside using tadalafil if appropriate—can improve both your erectile function and your long-term health.

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