Short answer: no. Both the Viagra and the Cialis labels say the safety and efficacy of combining them with other erectile dysfunction treatments have not been studied, and that the combination should not be used. The reasoning is about blood pressure, not about a missing “boost.”
Sildenafil (Viagra) and tadalafil (Cialis) work through the same enzyme, so adding one to the other does not add a different effect; it adds more of the same one, including the blood-pressure drop. If you have already taken both, the sections below explain which symptoms need urgent care.
What the labels actually say
The Viagra prescribing information has a section titled “Combination with other PDE5 Inhibitors or Other Erectile Dysfunction Therapies.” It states that the safety and efficacy of such combinations “have not been studied,” that they “may further lower blood pressure,” and that “the use of such combinations is not recommended.” The same section names Revatio, a sildenafil medicine used for pulmonary arterial hypertension.
The Cialis label goes a step further in its wording: it tells prescribers to inform patients not to take Cialis with other PDE5 inhibitors, naming Adcirca, the tadalafil product for pulmonary arterial hypertension. In short, neither manufacturer leaves room for “one in the morning, one at night.”
Why the combination is a problem
PDE5 inhibitors relax blood vessels, which helps blood flow to the penis and also lowers blood pressure slightly everywhere else. The Viagra label describes these as vasodilatory effects that are normally of little consequence but could matter in people with underlying cardiovascular disease, especially with sexual activity on top. The Cialis label puts a number on the baseline effect: in a clinical pharmacology study, a mean maximal decrease in supine blood pressure of 1.6/0.8 mm Hg relative to placebo in healthy subjects. That is small for one drug in healthy men. The labels are cautious about stacking it because nobody has measured the result in a real-world mix, in men with heart disease, diabetes or other blood pressure medicines.
There is also no evidence behind the idea that two PDE5 inhibitors are stronger for erections. The labels say efficacy of the combination has not been studied, which is different from saying it works better. If a single medicine is not working, the first step is a review for other causes, covered in Viagra not working? A safe checklist, not adding a second one.
| Concern | What the label says | Why it matters if two are taken |
|---|---|---|
| Blood pressure | Combination “may further lower blood pressure” (Viagra) | Dizziness, faintness and falls become more likely, especially if standing quickly, drinking alcohol or taking other blood pressure medicines |
| Prolonged erection | Seek emergency treatment if an erection lasts more than 4 hours; priapism is painful erection beyond 6 hours | Exposure to more drug can mean more risk; untreated priapism can cause permanent damage to penile tissue |
| Vision and hearing | Stop and seek care for sudden loss of vision in one or both eyes (NAION) or sudden decrease or loss of hearing | Duplicate dosing adds exposure to a drug class with these rare reports |
| Nitrates | Contraindicated with any form of organic nitrate | A second PDE5 drug extends the window where nitroglycerin could be dangerous |
The nitrate problem is bigger with two
If someone with heart disease has been told to keep nitroglycerin on hand, the combination matters in a specific way. The Viagra label says it is unknown when nitrates can be safely given after a dose, and adds that sildenafil levels at 24 hours are much lower than at peak. The Cialis label tells physicians to discuss what to do if chest pain needs nitroglycerin and states that at least 48 hours should have elapsed after the last tadalafil dose before a nitrate is given, in a life-threatening situation where a nitrate is medically necessary. Two drugs with different clearance times make that clock harder to count. Our guide to ED medicines, nitrates and blood pressure goes through the full picture.
If you already took both
People ask this after the fact more often than before. The scenario usually looks like: Viagra from an earlier prescription, Cialis from a new one, both in the cabinet, one taken and then, an hour later, the other “to be sure.” No label gives a rescue protocol for this, so the practical steps are about symptoms.
- Stay seated or lying down if you feel lightheaded; do not drive.
- Call 911 or go to an emergency department for chest pain, fainting, an erection lasting more than 4 hours, sudden loss of vision, or sudden hearing loss.
- Call Poison Help at 1-800-222-1222 if you are unsure and symptoms are mild; they can advise about a duplicated medicine and when to be seen.
- Tell the prescriber about the mix-up at the next contact, so the chart shows which product is the intended one.
Do not take nitroglycerin on your own initiative. If chest pain occurs, emergency responders need to know about both medicines and the timing.
Mixed-up bottles are the usual cause
Combinations happen less from curiosity than from medicine-cabinet drift. A man has a leftover sildenafil prescription, a different clinician writes tadalafil, and neither pharmacy knows about the other. The fix is dull and effective:
- Keep only the current ED medicine in the cabinet and ask the pharmacy how to dispose of the other.
- Use one pharmacy, or give each pharmacist the full list.
- Keep a note on your phone with the drug name, strength and prescriber.
- Ask whether you are on an alpha-blocker for the prostate or on blood pressure medicine. Both labels flag additive blood pressure lowering with alpha-blockers.
Other “combination” ideas that circulate
Search and forum chatter also mention mixing a PDE5 drug with supplements marketed as “natural,” with poppers, or with an injection. Products sold online as natural enhancers have been found by the FDA to contain hidden sildenafil or tadalafil, which turns a supplement into an unlabeled second PDE5 drug; our guide to hidden ingredients explains how to check FDA alerts. Poppers contain nitrites, and the labels’ nitrate contraindication covers “organic nitrates or organic nitrites in any form.” Another ED treatment such as an injection falls under the Viagra label’s “other treatments for erectile dysfunction.”
Daily tadalafil adds another wrinkle
People on a once-daily tadalafil product, sometimes prescribed for urinary symptoms of an enlarged prostate as well as erectile dysfunction, can forget that the drug is effectively always on board. The Cialis label notes that once-daily use provides continuous plasma tadalafil levels, which matters for interactions with nitrates, alpha-blockers, blood pressure medicines and heavy alcohol use. Adding a sildenafil tablet on top of that is a different situation from combining two as-needed pills. Our page on daily tadalafil or as needed explains the tradeoffs.
What a clinician can do instead
When one drug is not enough, the clinician has more useful options than doubling: checking timing and food, reviewing blood pressure and heart risk, adjusting the specific medicine or switching to another PDE5 inhibitor (not adding one), testing testosterone, or addressing diabetes, sleep apnea, depression and relationship factors. The page on PDE5 inhibitors compared explains how the three differ so a switch can be a deliberate choice.
What the labels say about taking too much
Overdose sections give a useful sense of how far from tested territory a double dose is. The Viagra label reports that in studies with healthy volunteers, single doses up to 800 mg produced adverse reactions similar to those at lower doses, but with increased incidence and severity, and that renal dialysis is not expected to speed clearance because sildenafil is highly protein bound. The Cialis label reports single doses up to 500 mg in healthy subjects with adverse events similar to those at lower doses, and says hemodialysis contributes negligibly to tadalafil elimination. These were controlled studies in healthy volunteers, not men with heart disease taking nitrates or alpha-blockers, and they say nothing about two different PDE5 drugs together, which neither label has studied.
Both labels also list groups for whom the starting point is cautious even with one drug: the Viagra label suggests considering a lower starting dose in men over 65 and in those with liver impairment or severe kidney impairment, and the Cialis label sets different handling for severe kidney impairment. If you fall into one of those groups, a duplicated dose carries more weight, and the prescriber should know the full list of products in your home.
Four ways people end up with both
The leftover and the new prescription. A man was prescribed sildenafil years ago, never finished the box, and now has tadalafil from a new clinician. Neither pharmacy knows about the other bottle. The fix is to bring both to the next visit and let the prescriber say which one stays.
The once-daily tadalafil patient. Someone on daily tadalafil, sometimes prescribed for an enlarged prostate as well as ED, takes sildenafil one night “for extra.” The Cialis label says it is not recommended to combine Cialis with alpha-blockers for BPH, and it notes caution when used for ED in men taking alpha-blockers; adding a second PDE5 drug piles one more blood-pressure effect onto an already layered regimen.
The man on a prostate or blood pressure medicine. Both the Viagra and Cialis labels advise caution when PDE5 inhibitors are used with alpha-blockers, because both classes are vasodilators with blood-pressure-lowering effects and, in some patients, the combination can lower blood pressure significantly and cause symptoms such as fainting. The vardenafil label adds that patients should be stable on the alpha-blocker before a PDE5 inhibitor is started. This is a one-drug question already; a second PDE5 inhibitor makes it harder.
Pills from a friend or abroad. A friend offers one “just in case,” or a product bought online does not say what it contains. The FDA warns that undeclared sildenafil or tadalafil in “natural” products can interact with nitrates and lower blood pressure to dangerous levels, so a prescription tablet plus a hidden one is a real combination scenario.
If you took both: symptom guide
| What you notice | Why the label cares | What to do |
|---|---|---|
| No symptoms at all | The risk window depends on each drug’s clearance; Cialis improved function for up to 36 hours per its label | Do not take a third dose; note the times; tell the prescriber at the next opportunity |
| Lightheaded, flushed, racing pulse | Blood pressure may be lower than expected | Sit or lie down, avoid alcohol, call Poison Help or the prescriber if it persists |
| Chest pain or pressure | Underlying heart disease can be affected by the blood-pressure drop; nitroglycerin is a hazard after a PDE5 inhibitor | Call 911; tell responders about both medicines and the times |
| Erection lasting more than 4 hours | Priapism can cause permanent damage if not treated | Go to an emergency department |
| Sudden loss of vision in one eye, or sudden hearing loss | Labelled reasons to stop and seek care (NAION; sudden hearing decrease) | Emergency evaluation |
Questions to ask the prescriber
- Which single PDE5 inhibitor is my plan, and what do I do with the other bottle?
- Do my blood pressure, prostate or heart medicines change which one is safer for me?
- If the medicine works only partly, what are the next steps that do not involve adding a second pill?
- Who do I call if I take too much by mistake?
Questions and answers
Is it okay to take them on different days?
The label statements concern combinations; they do not set a schedule for alternating. Cialis can improve erectile function up to 36 hours after dosing per the label, so a “next-day” Viagra overlaps more than people expect. Ask the prescriber before alternating.
What if my doctor prescribed both?
That would be unusual and deserves a direct question about why. Occasionally a patient takes sildenafil or tadalafil for pulmonary arterial hypertension under a specialist, which is a separate product and plan, and ED medicine must then be coordinated with that specialist.
Does alcohol make it worse?
The Cialis label says substantial alcohol use (5 units or more) in combination with the drug can increase orthostatic signs such as increased heart rate and decreased standing blood pressure. Alcohol and PDE5 inhibitors both act as mild vasodilators.
Sources
Evidence checked October 30, 2026. General information only; for emergencies call 911.