Tadalafil and Efavirenz: Can They Be Taken Together?

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What Is Tadalafil and What Is Efavirenz?

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 more blood to flow in when you are sexually aroused [4]. Tadalafil is available as an on-demand treatment (10 mg or 20 mg taken at least 30 minutes before sex, with effects lasting up to 36 hours) or as a daily low-dose tablet (2.5 mg or 5 mg) [4]. It requires sexual stimulation to work and does not increase sexual desire on its own.

Efavirenz is an antiretroviral medicine used to treat HIV-1 infection. It is a non-nucleoside reverse transcriptase inhibitor (NNRTI) that stops the virus from multiplying in your body [12]. Efavirenz is usually taken once daily as part of combination therapy with other HIV medicines. It is an important long-term treatment that helps keep the viral load low and supports immune function. Because efavirenz affects liver enzymes that break down many other medicines, it can interact with a wide range of drugs, including tadalafil.

Both medicines are prescription-only in the UK. If you are living with HIV and experiencing erectile dysfunction, it is important to discuss both conditions openly with your healthcare team so they can recommend the safest and most effective treatment plan for you [1][2].

How Do Tadalafil and Efavirenz Interact?

Efavirenz is a moderate to strong inducer of an enzyme system in the liver called CYP3A4. This enzyme is responsible for breaking down tadalafil in your body [4]. When efavirenz speeds up this enzyme, tadalafil is metabolised more quickly than usual, which lowers the amount of tadalafil in your bloodstream and shortens how long it stays active. As a result, the erectile dysfunction treatment may be less effective or wear off sooner than expected.

The British National Formulary notes that enzyme inducers such as efavirenz can reduce the plasma concentration of tadalafil, potentially leading to treatment failure [4]. This does not mean the combination is unsafe in terms of serious side effects like dangerously low blood pressure—unlike the absolute contraindication with nitrates or riociguat—but it does mean the medicine may simply not work well enough to help with erections.

Your prescriber will take this interaction into account during your consultation. They may suggest a higher dose of tadalafil, switch you to a different PDE5 inhibitor that is less affected by enzyme induction, or explore alternative ED treatments altogether. It is essential that you tell your prescriber about all your current medicines, including your HIV treatment, so they can make the best choice for you [2].

Why This Interaction Matters

The key concern with tadalafil and efavirenz is reduced effectiveness rather than a dangerous reaction. If tadalafil does not work as expected, it can be frustrating and may affect your confidence and quality of life. However, there are several other licensed ED treatments available in the UK, and your prescriber can help you find one that works well alongside your HIV medication. Open communication with your healthcare team is the most important step in managing both conditions successfully.

When to get urgent help

• Erection lasting more than 4 hours (priapism)—go to A&E immediately
• Sudden loss of vision in one or both eyes—seek same-day medical assessment
• Sudden decrease or loss of hearing, sometimes with ringing or dizziness—contact a doctor urgently
• Chest pain during or after sex—stop activity and seek medical help; do not take nitrates if you have used tadalafil in the past 48 hours
• Severe dizziness or fainting after taking tadalafil—sit or lie down and contact your prescriber if symptoms persist

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

What Your Prescriber Will Check Before Prescribing Tadalafil

When you request tadalafil through an online consultation at Cured Pharmacy, a UK-registered prescriber will review your medical history and current medicines carefully. They will ask specifically about any antiretroviral therapy you are taking, including efavirenz, to assess the risk of drug interactions [2][4]. The prescriber will also check for other conditions that might make tadalafil unsuitable, such as recent heart attack or stroke, severe heart failure, very low blood pressure, or a history of sudden vision loss (non-arteritic anterior ischaemic optic neuropathy, or NAION) [4].

If you are taking efavirenz, the prescriber may recommend starting with a standard or higher dose of tadalafil and monitoring how well it works for you. Alternatively, they might suggest a different PDE5 inhibitor—such as sildenafil, vardenafil, or avanafil—if one of these is less likely to be affected by your HIV treatment, though all PDE5 inhibitors can be influenced by enzyme inducers to some degree [3][5][6]. The prescriber will also ask about other medicines you take, including blood pressure tablets, alpha-blockers (used for prostate symptoms), and any over-the-counter or herbal products like St John's wort, which is also an enzyme inducer.

It is important to be honest and thorough when completing your consultation. Do not stop or change your HIV medication without speaking to your HIV specialist, as consistent antiretroviral therapy is essential for your health. The goal is to find an ED treatment that fits safely into your overall treatment plan [1][2].

Practical Advice for Taking Tadalafil with Efavirenz

If your prescriber approves tadalafil while you are taking efavirenz, follow the dosing instructions carefully. Take tadalafil at least 30 minutes before sexual activity if using the on-demand tablets (10 mg or 20 mg), and remember that sexual stimulation is needed for the medicine to work [4]. Because efavirenz may reduce how long tadalafil stays active, you might find that the effect does not last the full 36 hours that is typical for tadalafil. Keep a note of how well the treatment works and report back to your prescriber if you feel it is not effective enough.

Avoid drinking large amounts of alcohol, as this can make erectile dysfunction worse and add to the blood-pressure-lowering effect of tadalafil, increasing the risk of dizziness or fainting [4]. Grapefruit juice can also affect how your body processes tadalafil and should be avoided. Do not take more than one dose of tadalafil in 24 hours, and never combine it with another PDE5 inhibitor or with nitrates, nicorandil, riociguat, or poppers, as these combinations can cause a dangerous drop in blood pressure [4].

If tadalafil does not work well for you, do not simply increase the dose on your own. Contact your prescriber to discuss your options. There are other ED treatments available, including different PDE5 inhibitors, and your prescriber can help you find the most suitable one. Remember that erectile dysfunction can have physical and psychological causes, and addressing underlying factors—such as cardiovascular health, diabetes control, stress, or anxiety—can also improve your symptoms [1][2].

Monitoring and Follow-Up

After starting tadalafil, pay attention to how your body responds. If you notice any unexpected side effects—such as severe headache, chest pain, prolonged erection lasting more than four hours, or sudden changes in vision or hearing—seek medical help immediately. Regular follow-up with both your HIV specialist and your GP or prescriber is important to ensure all your treatments are working well together and that your overall health is being managed effectively [2].

At a glance

Are There Alternative ED Treatments If Tadalafil Doesn't Work?

If tadalafil is not effective while you are taking efavirenz, several other options are available. Sildenafil (the active ingredient in Viagra) is another PDE5 inhibitor that works in a similar way, taken about one hour before sex with effects lasting around four to six hours [3]. Vardenafil (Levitra) and avanafil (Spedra) are also licensed PDE5 inhibitors in the UK, each with slightly different timing and duration profiles [5][6]. All of these medicines can be affected by enzyme inducers like efavirenz, but individual responses vary, and one may work better for you than another.

Your prescriber may also consider non-tablet treatments if oral medicines are not suitable or effective. Alprostadil is available as a cream applied to the tip of the penis (Vitaros) or as an injection into the side of the penis (Caverject) [7]. These treatments work locally rather than being absorbed into the bloodstream, so they are not affected by drug interactions in the same way. Vacuum erection devices and penile implants are other options that can be discussed with a specialist if needed [2].

It is also worth exploring whether any underlying health conditions are contributing to your erectile dysfunction. HIV itself, as well as some antiretroviral medicines, can affect sexual function, and psychological factors such as anxiety or depression are common [1]. Your GP or HIV clinic can refer you to a specialist or counsellor if appropriate. Lifestyle changes—such as regular exercise, a healthy diet, stopping smoking, and reducing alcohol—can also make a significant difference to erectile function and overall wellbeing [1][2].

Warning Signs and When to Seek Urgent Help

Most men tolerate tadalafil well, but it is important to know the warning signs that require urgent medical attention. If you develop an erection that lasts longer than four hours (priapism), go to A&E immediately, as this can cause permanent damage to the penis if not treated quickly [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 that need same-day medical assessment [4].

If you experience chest pain during or after sexual activity, stop and seek medical help. Do not take nitrate medicines (such as GTN spray) to relieve chest pain if you have taken tadalafil in the past 48 hours, as the combination can cause a dangerous drop in blood pressure [4]. Tell the paramedics or doctor that you have taken tadalafil so they can treat you safely. If you feel dizzy, lightheaded, or faint after taking tadalafil, sit or lie down and avoid driving or operating machinery until you feel better. Contact your prescriber if these symptoms are severe or do not improve.

Common side effects of tadalafil include headache, indigestion, back pain, muscle aches, flushing, and nasal congestion [4]. These are usually mild and temporary. If side effects are troublesome or persistent, speak to your prescriber, who may adjust your dose or suggest a different treatment. Never stop your HIV medication without advice from your HIV specialist, even if you think it is causing problems with your ED treatment. Managing both conditions together requires coordination between your healthcare providers, and Cured Pharmacy's prescribers work within the NHS framework to ensure safe, joined-up care [2].

Reporting Side Effects

If you experience any side effects from tadalafil, whether listed in the patient information leaflet or not, you can report them via the Yellow Card Scheme at yellowcard.mhra.gov.uk or by searching for the MHRA Yellow Card app. Reporting helps improve the safety information available for all patients. You can also discuss any concerns with the Cured Pharmacy team or your GP.

In summary

• Tadalafil and efavirenz can be taken together, but efavirenz may reduce tadalafil's effectiveness.
• Efavirenz speeds up how your body breaks down tadalafil, so it may not last as long.
• Your prescriber may adjust the dose or suggest an alternative ED treatment if tadalafil doesn't work well.
• Never stop your HIV medication without advice from your specialist.
• All ED treatments require an online consultation reviewed by a UK prescriber.

Frequently Asked Questions