Tadalafil and Cobicistat: Can They Be Taken Together?

Takes less than 2 minutes to complete 100% online

Key takeaways

• Tadalafil and cobicistat can be used together, but the tadalafil dose must be reduced to a maximum of 10 mg in 72 hours.
• Cobicistat blocks the enzyme that breaks down tadalafil, causing higher blood levels and increased risk of side effects.
• Daily tadalafil is not recommended with cobicistat; on-demand dosing at a lower strength is safer.
• Always declare cobicistat and all HIV medicines during your consultation so the prescriber can adjust your dose safely.
• Other ED medicines also interact with cobicistat; your prescriber will choose the safest option for you.

What is tadalafil and cobicistat?

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 [3][4]. Tadalafil is available as on-demand tablets (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). It is the active ingredient in branded Cialis and is also available as a generic medicine.

Cobicistat is a prescription medicine used alongside certain antiretroviral drugs to treat HIV infection. It does not fight HIV itself but acts as a 'booster' by blocking the enzyme CYP3A4 in the liver and gut, which normally breaks down HIV medicines. By slowing this breakdown, cobicistat helps maintain higher, more effective levels of the HIV treatment in your bloodstream [12]. Cobicistat is found in combination tablets such as Evotaz, Genvoya, Stribild, and Symtuza.

Because cobicistat blocks CYP3A4, it also slows the breakdown of many other medicines that rely on the same enzyme—including tadalafil. This means tadalafil stays in your body longer and reaches higher concentrations, which increases both its effects and the risk of side effects if the dose is not adjusted.

How do tadalafil and cobicistat interact?

When you take tadalafil and cobicistat together, cobicistat blocks the CYP3A4 enzyme that would normally break down tadalafil in your liver. As a result, tadalafil levels in your blood can rise significantly—sometimes more than double the usual amount. This is known as a pharmacokinetic interaction, meaning one medicine changes how much of the other medicine is present in your body [4][12].

Higher tadalafil levels 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 cause a more pronounced drop, especially if you are also taking other medicines that affect blood pressure. This is why dose adjustment is essential.

The interaction is predictable and well-documented in the tadalafil Summary of Product Characteristics. Your prescriber will take cobicistat into account when deciding whether tadalafil is suitable for you and, if so, what dose to prescribe. You should never adjust the dose yourself or take tadalafil from another source without declaring all your current medicines.

Why CYP3A4 matters

CYP3A4 is one of the most important enzymes in the body for breaking down medicines. It is found mainly in the liver and the lining of the gut. Many commonly prescribed drugs—including tadalafil, some antibiotics, antifungals, and HIV medicines—are processed by CYP3A4. When a potent CYP3A4 inhibitor like cobicistat is taken, it can slow the breakdown of these medicines, leading to higher blood levels and a greater risk of side effects. Understanding this interaction helps your prescriber choose the safest dose for you.

At a glance

What dose of tadalafil is safe with cobicistat?

If you are taking cobicistat, the maximum recommended dose of tadalafil is lower than usual. For on-demand use (taken before sex), the British National Formulary advises a maximum single dose of 10 mg of tadalafil in any 72-hour period [4]. This is a significant reduction from the standard maximum of 20 mg in 24 hours for men not taking a CYP3A4 inhibitor.

Daily tadalafil (the lower-dose option taken every day) is generally not recommended when you are on a potent CYP3A4 inhibitor such as cobicistat, because even the small daily dose can accumulate to higher-than-intended levels. Your prescriber will review your full medication list and decide whether on-demand tadalafil at a reduced dose is appropriate, or whether an alternative ED treatment might be safer.

It is essential that you declare cobicistat (and any other HIV medicines) during your online consultation. The prescriber will check the Summary of Product Characteristics for both medicines and may contact your HIV specialist or GP if further advice is needed. Never take a higher dose than prescribed, and do not take tadalafil more frequently than advised, even if you feel the effect is weaker than expected.

What your prescriber checks before approving tadalafil and cobicistat together

During your online consultation at Cured Pharmacy, the prescriber will ask detailed questions about your current medicines, including the exact name and dose of your HIV treatment. They will check for cobicistat in combination tablets and confirm that you are not taking any other potent CYP3A4 inhibitors at the same time, such as ritonavir, ketoconazole, itraconazole, or clarithromycin, which would further increase tadalafil levels.

The prescriber will also review your blood pressure, cardiovascular history, and any other conditions that might make ED treatment less safe. They will check that you are not taking nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, or recreational drugs called 'poppers', because combining any of these with tadalafil can cause a dangerous drop in blood pressure. If you take an alpha-blocker for prostate symptoms (such as tamsulosin or doxazosin), the prescriber will ensure you are stable on that medicine and may start you on the lowest tadalafil dose.

If the prescriber is satisfied that tadalafil is suitable, they will issue a prescription for the adjusted dose. The medicine will be dispensed by our GPhC-registered pharmacy and delivered discreetly to your address. You should not take tadalafil from any other source while on cobicistat without a prescriber reviewing the combination, as this could lead to an unsafe dose.

Why you must declare all medicines

It is a legal and safety requirement to provide accurate information about all medicines you take—prescription, over-the-counter, herbal, and recreational. Some interactions are life-threatening, and others can make treatment ineffective or cause serious side effects. Your prescriber cannot assess risk without a complete picture. All information you provide is confidential and handled in line with UK data protection law.

Tadalafil and cobicistat: practical advice for safe use

If you are prescribed tadalafil while taking cobicistat, take it exactly as directed. For on-demand use, take one tablet at least 30 minutes before you plan to have sex. Do not take more than one dose in 72 hours. Tadalafil requires sexual stimulation to work; it will not cause an erection on its own. Avoid drinking large amounts of alcohol, as this can make it harder to get an erection and may increase the risk of dizziness or low blood pressure.

Do not take tadalafil with grapefruit or grapefruit juice, as this can also raise tadalafil levels unpredictably. If you experience side effects such as severe headache, dizziness, chest pain, or an erection lasting more than four hours, seek medical help immediately. If you develop sudden loss of vision or hearing, stop taking tadalafil and contact a doctor the same day.

Keep your HIV specialist or GP informed that you are using tadalafil, especially if your HIV treatment changes. If cobicistat is stopped or replaced with a different booster (such as ritonavir) or a regimen that does not need a booster, the safe dose of tadalafil may change. Never share your tadalafil with others, and store it in a cool, dry place out of reach of children.

Other ED treatments and cobicistat interactions

All PDE5 inhibitors—sildenafil (Viagra), vardenafil (Levitra), and avanafil (Spedra)—are broken down by CYP3A4, so cobicistat affects them all. However, the degree of interaction and the safety advice differ. Vardenafil and avanafil are more sensitive to CYP3A4 inhibition, and their use with potent inhibitors like cobicistat is generally contraindicated or not recommended [5][6]. Sildenafil can be used with dose adjustment (usually a lower starting dose and longer gap between doses), but the prescriber must check the latest guidance [3].

If tadalafil is not suitable or effective for you, your prescriber may discuss alternative treatments. These include alprostadil, which is applied as a cream (Vitaros) or given by injection (Caverject) and does not interact with cobicistat because it works locally rather than being broken down by the liver [7]. A vacuum erection device is another non-drug option. Your GP or a specialist can also explore whether any underlying causes of ED—such as diabetes, high blood pressure, or low testosterone—can be treated.

It is important to remember that no two PDE5 inhibitors should be taken together, and you should not switch between them without your prescriber's advice. If you are considering an over-the-counter option such as Viagra Connect (sildenafil 50 mg) or Eroxon gel, you must still declare cobicistat to the pharmacist, as the interaction applies to all forms of sildenafil.

Can I use Viagra Connect with cobicistat?

Viagra Connect is a pharmacy medicine containing sildenafil 50 mg. Although it is available without a prescription, you must have a consultation with a pharmacist, who will ask about all your medicines. If you are taking cobicistat, the pharmacist may advise that Viagra Connect is not suitable, or they may refer you to your GP or an online prescriber who can assess the interaction and prescribe a lower, safer dose of sildenafil if appropriate.

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 – stop tadalafil and seek same-day medical advice
• Chest pain during or after sex – call 999; do not take nitrate medicines (GTN) if you have used tadalafil in the last 48 hours
• Severe dizziness, fainting, or very low blood pressure – seek urgent medical help
• Sudden decrease or loss of hearing – stop tadalafil and contact your GP or NHS 111 the same day

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