Tadalafil and Atazanavir: Safe Use & Interaction

Takes less than 2 minutes to complete 100% online

What is tadalafil and atazanavir?

Tadalafil is a medicine used to treat erectile dysfunction (ED) and belongs to a group called PDE5 inhibitors [4]. It works by relaxing blood vessels in the penis, allowing more blood to flow in when you are sexually aroused. Tadalafil is available as on-demand tablets (usually 10 mg or 20 mg taken at least 30 minutes before sex, with effects lasting up to 36 hours) or as a lower daily dose (2.5 mg or 5 mg) [4]. It requires sexual stimulation to work and does not cause an automatic erection.

Atazanavir is an antiretroviral medicine used to treat HIV infection [12]. It is a protease inhibitor, which means it blocks an enzyme that HIV needs to replicate. Atazanavir is often prescribed alongside other HIV medicines and sometimes with a 'booster' drug called ritonavir or cobicistat, which further increases its levels in the blood. Because atazanavir (and its boosters) also block the CYP3A4 enzyme in the liver, they can significantly affect how your body processes other medicines, including tadalafil [4][12].

How do tadalafil and atazanavir interact?

The interaction between tadalafil and atazanavir happens in your liver. Tadalafil is normally broken down by an enzyme called CYP3A4. Atazanavir is a potent inhibitor of this enzyme, meaning it blocks or slows down the enzyme's activity [4][12]. When you take atazanavir, your body cannot break down tadalafil as quickly as usual, so tadalafil levels in your blood become higher and stay elevated for longer.

Higher levels of tadalafil can increase the chance of side effects such as headache, flushing, indigestion, back pain, muscle aches, and dizziness. More importantly, tadalafil lowers blood pressure slightly, and higher levels may lead to a more pronounced drop, which can cause light-headedness or fainting, especially if you are also taking other blood-pressure-lowering medicines [4]. This interaction is predictable and well documented, so prescribers routinely adjust the tadalafil dose when it is used alongside atazanavir or other potent CYP3A4 inhibitors.

Does it matter if atazanavir is boosted?

Yes, it does. Atazanavir is often prescribed with ritonavir or cobicistat, which are themselves very strong CYP3A4 inhibitors [12]. When atazanavir is boosted in this way, the effect on tadalafil levels is even greater. Your prescriber will take this into account and may recommend an even lower dose of tadalafil or a longer gap between doses to keep you safe. Always tell your prescriber or pharmacist the exact formulation of atazanavir you are taking, including any booster medicines.

When to get urgent help

• Chest pain or discomfort during or after sex—call 999 immediately and do not take nitrates
• 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—stop tadalafil and seek urgent medical help
• Sudden decrease or loss of hearing, with or without ringing or dizziness—stop tadalafil and contact a doctor urgently
• Severe dizziness, fainting, or feeling very unwell after taking tadalafil—call NHS 111 or see your GP the same day

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

What dose adjustments are needed for tadalafil and atazanavir?

Because atazanavir raises tadalafil levels, the dose of tadalafil usually needs to be reduced [4]. For on-demand use (when you take tadalafil only before sexual activity), the maximum recommended dose is typically 10 mg, and you should not take it more often than once every 72 hours (three days). Some prescribers may start you on an even lower dose, such as 5 mg, depending on your overall health and other medicines.

If you are considering daily tadalafil (a low dose taken every day), this is generally not recommended when you are taking a potent CYP3A4 inhibitor like atazanavir, especially if it is boosted with ritonavir or cobicistat [4]. The risk of side effects becomes too high with continuous exposure. Your prescriber will discuss the best dosing schedule for your individual circumstances during your consultation.

Never adjust the dose yourself or take tadalafil more frequently than advised. If you feel the lower dose is not effective enough, speak to your prescriber—they may be able to suggest alternative ED treatments or review your HIV medication regimen in consultation with your HIV specialist.

What does your prescriber check before approving tadalafil with atazanavir?

When you request tadalafil through Cured Pharmacy's online consultation, a UK-registered prescriber reviews your full medical history and current medicines [2]. They will specifically check that you are taking atazanavir (and any booster), note any other medicines that affect your blood pressure or interact with tadalafil, and assess your cardiovascular health. Tadalafil is not suitable if sexual activity itself is inadvisable—for example, after a recent heart attack or stroke, or if you have unstable angina or severe heart failure [4].

Your prescriber will also confirm that you are not taking any medicines that must never be combined with tadalafil, such as nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, or recreational drugs known as 'poppers' (amyl or alkyl nitrites) [3][4]. Combining tadalafil with these can cause a dangerous drop in blood pressure. If you take an alpha-blocker for prostate symptoms or high blood pressure (such as doxazosin or tamsulosin), your prescriber will ensure you are stable on that medicine and start tadalafil at the lowest dose to minimise the risk of dizziness [4].

It is essential that you list all your current medicines accurately in the consultation, including over-the-counter products and supplements. Your prescriber may also liaise with your GP or HIV specialist if needed to ensure your treatment is coordinated and safe.

Can I take other ED medicines with atazanavir?

Other PDE5 inhibitors—sildenafil (Viagra), vardenafil (Levitra), and avanafil (Spedra)—are also affected by atazanavir, though to different degrees [3][5][6]. Sildenafil requires a lower starting dose (typically 25 mg) and less frequent use. Vardenafil and avanafil are generally contraindicated or not recommended with potent CYP3A4 inhibitors like boosted atazanavir because the interaction is harder to manage safely [5][6]. Your prescriber will choose the most appropriate option based on the latest guidance and your individual needs. Never take two different PDE5 inhibitors together.

At a glance

Practical advice for taking tadalafil and atazanavir together

Take tadalafil exactly as prescribed—do not exceed the recommended dose or frequency. If you have been advised to take tadalafil on-demand, plan ahead: take it at least 30 minutes before you anticipate sexual activity, and remember that you should not take another dose for at least 72 hours [4]. Tadalafil requires sexual stimulation to work, so it will not cause an erection on its own.

Avoid drinking large amounts of alcohol when using tadalafil, as alcohol can worsen erectile dysfunction and add to the blood-pressure-lowering effect, increasing the risk of dizziness or fainting [4]. Grapefruit juice can also raise tadalafil levels further and should be avoided. If you experience side effects such as severe headache, dizziness, chest pain during sex, or an erection lasting more than four hours, seek medical help immediately.

Continue taking your atazanavir and other HIV medicines exactly as prescribed by your HIV specialist. Do not stop or change your HIV treatment without medical advice. If you are prescribed a new medicine by another doctor or buy something over the counter, always check with your pharmacist or prescriber that it is safe to take alongside tadalafil and atazanavir. Keeping an up-to-date list of all your medicines can help avoid harmful interactions.

When to seek medical help and what to watch for

Most men tolerate tadalafil well, even at adjusted doses, but you should be aware of warning signs that need urgent attention. If you develop chest pain or discomfort during or after sex, stop the activity and seek immediate medical help—call 999 or go to A&E [4]. Do not take any nitrate medicine (such as GTN spray) if you have used tadalafil in the past 48 hours, as this combination can be life-threatening.

An erection that lasts longer than four hours (priapism) is a medical emergency and requires immediate treatment to prevent permanent damage to the penis [4]. 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—stop taking tadalafil and seek urgent medical advice [4].

If you experience severe dizziness, fainting, or feel unusually unwell after taking tadalafil, contact your GP or call NHS 111 for advice. It is also important to see your GP if your erectile dysfunction is new or worsening, as ED can be an early sign of underlying health conditions such as diabetes or cardiovascular disease [1][2]. Your GP can arrange tests and work with your HIV team to optimise your overall health and treatment.

Can I get tadalafil through Cured Pharmacy if I take atazanavir?

Yes, you can request tadalafil through Cured Pharmacy's online consultation service. During the consultation, you will be asked to provide details of all your current medicines, including atazanavir and any booster drugs. A UK-registered prescriber will review your information and, if appropriate, approve a safe, adjusted dose of tadalafil for you. Prescription medicines are only supplied after this clinical assessment. If you have any questions or your circumstances change, our pharmacy team is here to help—contact us for advice at any time.

In summary

• Atazanavir raises tadalafil levels by blocking the enzyme that breaks it down, so dose adjustment is essential.
• Maximum tadalafil dose is usually 10 mg every 72 hours when taking atazanavir; daily tadalafil is not recommended.
• Boosted atazanavir (with ritonavir or cobicistat) has an even stronger effect and requires stricter dose limits.
• Always tell your prescriber about all HIV medicines and boosters during your consultation for safe treatment.
• Seek urgent help for chest pain, erection over 4 hours, or sudden vision or hearing loss.

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.

Faq