Sildenafil and Tadalafil Together: Labels and Evidence

Two PDE5 inhibitors, one dose. The labels, the one systematic review and the questions to ask a prescriber.

Taking sildenafil (Viagra) and tadalafil (Cialis) together is not something their FDA labels support. Both labels say the safety and efficacy of combining the drug with another PDE5 inhibitor or other ED treatment have not been studied, and both tell prescribers to warn patients not to take them together.¹² The two drugs act the same way, so the shared effects, including lower blood pressure, headache and flushing, can add up rather than stay separate. A clinician may still prescribe a combination in selected cases, but that is a judgment made outside the labels, not a standard regimen.

This guide covers what the labels say, what the one systematic review of oral combination therapy found, why compounded combination products exist, and what to ask before using one.

Why is combining sildenafil and tadalafil a question at all?

Sildenafil and tadalafil are both PDE5 inhibitors, and they differ mainly in timing. Sildenafil reaches its peak blood level at a median of about 60 minutes in the fasted state, and the label recommends no more than one dose per day.¹ Tadalafil has a mean terminal half-life of 17.5 hours, improves erectile function compared with placebo for up to 36 hours after a dose, and carries the same once-per-day ceiling in most patients.²

The idea behind pairing them is simple: a quick-acting drug and a long-acting drug in one dose. The labels do not endorse it, and the reason is practical. Each label sets dose limits that assume the patient takes that drug alone.¹²

What do the FDA labels say about combinations?

The practical reading: a second PDE5 inhibitor adds a second source of the same blood pressure effect, and no dose table exists for the pair. For the full list of drugs that rule out any PDE5 inhibitor, see our guide to ED medication interactions.

Is there evidence that combining them helps?

The best summary is a 2019 systematic review of oral combination therapy in men whose PDE5 inhibitor alone had failed. It reported that chronic tadalafil alone and chronic tadalafil combined with on-demand sildenafil produced similar IIEF-5 score improvements.³ In other words, adding sildenafil to tadalafil did not show an extra gain in that comparison. The review also found no superior effect from adding an alpha-blocker, and it called for more research on other add-ons. Its conclusion was that low-dose daily PDE5 inhibitor treatment can be attempted when standard on-demand regimens fail, and that there is an unmet need for oral options in nonresponders.³

That is a review of a small and varied literature, not a large trial of a two-drug pill, and it concerned men who had not responded to a single drug. It does not show that a combination is safer or stronger for a man starting treatment. The same review notes that 30% to 40% of men show little or no response to on-demand PDE5 inhibitor monotherapy, which is the group these products are aimed at.³

What should be tried before combining?

Because a combination is outside the labels, the usual first steps are to check the basics of single-drug use. Our guide on ED and blood pressure medicines covers a common reason doses need adjusting. In practice, a clinician is likely to look at the following before suggesting a second PDE5 inhibitor:

• Timing and dose. Sildenafil taken after a high-fat meal is absorbed more slowly, with a mean delay of 60 minutes to peak level in the label data, so timing relative to food matters.¹
• Whether tadalafil daily dosing has been tried. The review above points to chronic low-dose tadalafil as an option after on-demand failure.³²
• Other medicines. Alpha-blockers and antihypertensives add to the blood pressure effect, and sildenafil should be started at 25 mg when taken with an alpha-blocker.¹
• Other causes. Low testosterone, diabetes and heart disease can all sit behind a poor response; see ED and heart health.

What are compounded combination products?

Several telehealth services sell compounded products that put more than one ED drug in a single dose, often as a tablet or film that dissolves under the tongue. The FDA states that compounded drugs are not FDA-approved and that it does not verify their safety, effectiveness or quality before they reach patients.⁴ A compounded combination has no label of its own, so the label statements above, that combinations have not been studied, apply to it as well.¹²

A 2023 review of direct-to-consumer ED platforms and a 2025 review of information quality on online telepharmacy sites found wide variation in what services tell patients, which is a reason to ask a prescriber directly what a product contains and why.⁵⁶

One compounded option: Quattro from Vea Health (sponsored)

We have a financial relationship with Vea Health, so this section is a sponsored placement, and it is included because the topic is a combination product. Vea Health describes Quattro as a "4-in-1 protocol" that combines apomorphine, vardenafil, sildenafil and tadalafil, dissolves under the tongue, is prescribed after an online evaluation reviewed by a clinician, and is shipped from a U.S. state-licensed 503A compounding pharmacy.⁷ The page says a card is not charged until a clinician approves the prescription, and that the product is subject to clinician approval.⁷

Quattro is a compounded product, so the FDA has not reviewed it for safety, effectiveness or quality, and the page we loaded does not state strengths or discuss interactions.⁴⁷ It contains three PDE5 inhibitors, which is more than the sildenafil and tadalafil pair discussed above, and the Viagra and Cialis labels say combinations like this have not been studied.¹² We make no claim that it is stronger, faster or safer than a single FDA-approved tablet. Whether it is appropriate depends on the medicines a person takes, their heart health and what a clinician judges safe.

Questions to ask before taking two ED drugs

• What is the exact strength of each drug in the dose, and is it a single compounded product or two separate prescriptions?
• What is the maximum number of doses in 24 hours, given that both labels cap use at once per day?¹²
• Does my blood pressure treatment or any alpha-blocker change the plan?¹
• What should I do if I feel faint, or if an erection lasts more than four hours?¹

Safety information

Sildenafil, tadalafil and vardenafil must never be taken with nitrates in any form or with riociguat. An erection lasting more than four hours needs emergency care, as does sudden hearing loss, where the Viagra label says to stop the drug and seek prompt medical attention.¹² Dizziness or fainting after taking any ED drug should be reported to a clinician. Only a licensed clinician who knows your history and medicines can say whether any ED medication, single or combined, is appropriate.

Questions readers ask

Can you take sildenafil and tadalafil together?

The Viagra and Cialis labels say the safety and efficacy of combining either drug with another PDE5 inhibitor have not been studied, and tell prescribers to advise patients not to take them together. A clinician may prescribe a combination in selected cases, but that is outside the labels.

Is there a safe dose of sildenafil and tadalafil together?

No dose for the pair appears in either label. Each label sets a maximum frequency of once per day for its own drug, and any combined dose is a prescriber's judgment, not an FDA-established regimen.

Does adding sildenafil to tadalafil improve results?

A 2019 systematic review of men whose single-drug treatment had failed found that chronic tadalafil alone and chronic tadalafil with on-demand sildenafil gave similar IIEF-5 improvements. The literature is small and varied.

Are sildenafil and tadalafil combination tablets FDA-approved?

No combination tablet of the two is FDA-approved. Compounded combination products are not FDA-approved, and the FDA does not verify their safety, effectiveness or quality.

What are the main risks of combining ED drugs?

Both drugs lower blood pressure, so effects such as dizziness and fainting can add up. Nitrates and riociguat rule out every PDE5 inhibitor, and an erection lasting more than four hours needs emergency care.

Further reading

Part of our guide: How ED Medications Work: Timing, Food, Interactions and Combinations

• Sildenafil Headache: How Common Is It?
• Tadalafil With Alcohol: How Much Is Too Much?
• What Is Tadalafil Used For? The Three Approved Uses
• Tadalafil Brand Names: Which Brand Is Used for What