Can you take Viagra and Cialis together? No. The product information for both medicines says that combining them with another medicine of the same kind, or with any other treatment for erectile dysfunction, has not been studied and is not recommended, and the Australian Cialis leaflet lists sildenafil — the medicine in Viagra — among the medicines that interact with it. If one tablet is not working well enough, the answer is a change of dose, timing or medicine with your doctor, not a second tablet.
Why shouldn't Viagra and Cialis be taken together?
Because they are the same kind of medicine. Sildenafil (Viagra) and tadalafil (Cialis) are both PDE5 inhibitors (healthdirect), and neither label backs combination treatments. The sildenafil label says the safety and efficacy of combining it with other PDE5 inhibitors or other treatments for erectile dysfunction "have not been studied. Therefore the use of such combinations is not recommended" (EMA — Viagra); the tadalafil label says patients "should be informed not to take CIALIS in such combinations" (EMA — Cialis). The Australian leaflets say the same in plain words: the Cialis list of interacting medicines includes "other PDE5 inhibitors such as sildenafil", and the Viagra leaflet asks you to check with your doctor if you are "taking or using any other treatment for impotence" (Cialis CMI; Viagra CMI). Each medicine's other possible drug interactions are listed in full elsewhere.
What can happen if you take both?
The pair has not been studied, but more medicine of this kind brings more side effects rather than a better erection: with sildenafil alone, 200 mg was no more effective than the usual doses but caused more headache, flushing, dizziness, indigestion, nasal congestion and altered vision (EMA — Viagra). The common side effects of these medicines are headache, facial flushing, a blocked nose and indigestion; less often there are vision changes, sudden hearing loss, dizziness and fainting, or priapism, a painful erection that won't go down (healthdirect). An erection lasting more than 4 hours needs the nearest hospital emergency department (healthdirect — Sildenafil). If you think you have taken too much, the Australian leaflets say to phone the Poisons Information Centre on 13 11 26, contact your doctor or go to the nearest emergency department. Doubling up on one medicine is its own question: is it safe to take more than one Viagra?
How long should you wait between Cialis and Viagra?
No label gives a waiting time, so ask your doctor before switching from one to the other. What the labels do give is how long each lasts. Tadalafil has a half-life of 17.5 hours (EMA — Cialis) and works for up to 36 hours (Cialis CMI), so a Cialis tablet can still be working a day and a half later. Sildenafil's half-life is 3 to 5 hours (EMA — Viagra) and its effect lasts up to 4 hours (healthdirect — Sildenafil). Each has its own limit too: "Do not take more than one dose of VIAGRA a day", and Cialis should not be taken more than once a day (Viagra and Cialis CMIs).
Can you take daily Cialis and Viagra when you need it?
No. Once-a-day Cialis (5 mg) is for men who expect to use it at least twice a week, and it lets you get an erection with sexual stimulation "at any time point during the 24 hours of the day" (Cialis CMI) — so a Viagra on top is the same combination the labels advise against. The Cialis leaflet rules out even mixing its own two schedules: "Do not take once-a-day dosing and on-demand dosing concurrently". How the two Cialis schedules compare: daily or on-demand Cialis?
What if one of them isn't working well enough?
Go back to the doctor who prescribed it: healthdirect notes that your doctor checks whether the medicine is working and "can adjust the dose if necessary". Sildenafil usually starts at 50 mg and can go up to 100 mg or down to 25 mg; tadalafil on demand starts at 10 mg and can go up to 20 mg (EMA — Viagra overview; EMA — Cialis overview). Timing matters as well: Viagra about one hour before sex, and it may take longer after a heavy meal; Cialis at least 30–60 minutes before; and neither works without sexual stimulation. If tablets don't suit, healthdirect lists alprostadil injections, vacuum erection devices and counselling or sex therapy. The one-medicine rule covers those pairs too: Viagra and Levitra together and Viagra with Trimix.
Does Revatio count as a second medicine?
Yes. Revatio also contains sildenafil and is used for high blood pressure in the lungs; the Viagra leaflet asks you to check with your doctor if you take it, and the sildenafil label puts Revatio in the same not-recommended list. The Cialis leaflet's list likewise covers PDE5 inhibitors used for that condition.
The short answer
Take one ED medicine at a time, and no more than one tablet of it a day. If it is not working, the dose, the timing or a different medicine is a question for your doctor — and nitrates, for chest pain, are never allowed with either. Every other combination is covered in our guide to taking Viagra or Cialis with other medicines.
