Viagra vs Cialis: sildenafil and tadalafil compared
Viagra (sildenafil) and Cialis (tadalafil) treat erectile dysfunction the same way, and both are now available as generics. The practical differences are timing: how long each takes to work, how long it lasts, whether food matters, and whether a low daily dose is an option.
Updated October 15, 2026
At a glance
- How it works
- Viagra
- PDE5 inhibitor
- Cialis
- PDE5 inhibitor
- When to take it
- Viagra
- About an hour before sex; a heavy, fatty meal delays it
- Cialis
- At least 30 minutes before; food makes little difference
- How long it lasts
- Viagra
- Around four to six hours
- Cialis
- Up to about 36 hours
- Daily low-dose option
- Viagra
- No
- Cialis
- Yes, also approved for urinary symptoms of an enlarged prostate
- Generic available
- Viagra
- Yes
- Cialis
- Yes
Viagra sildenafil; also sold as Revatio for pulmonary hypertension | Cialis tadalafil; also approved for an enlarged prostate | |
|---|---|---|
| How it works | PDE5 inhibitor | PDE5 inhibitor |
| When to take it | About an hour before sex; a heavy, fatty meal delays it | At least 30 minutes before; food makes little difference |
| How long it lasts | Around four to six hours | Up to about 36 hours |
| Daily low-dose option | No | Yes, also approved for urinary symptoms of an enlarged prostate |
| Generic available | Yes | Yes |
Choosing between them
Tadalafil’s long window suits people who prefer not to time a dose, and its daily low dose treats both erectile dysfunction and prostate symptoms. Sildenafil acts and wears off sooner, which some people prefer. Side effects overlap: headache, flushing and a stuffy nose for both, a temporary blue tinge to vision more often with sildenafil, and back or muscle aches more often with tadalafil.
Safety rules that apply to both
Neither may be taken with nitrates such as nitroglycerin, or with riociguat, because the combination can drop blood pressure dangerously. Care is needed with alpha blockers. Chest pain during sex, an erection lasting more than four hours, or sudden loss of vision or hearing needs urgent care.
Cost
Both are available as generics, and each pharmacy sets its own cash price, so comparing quotes for your exact strength and quantity is worthwhile. Sildenafil also comes as a 20 mg tablet labeled for pulmonary hypertension, so make sure each quote is for the tablets your prescription actually lists. A plan may limit quantities for erectile dysfunction or not cover it at all, so check your plan’s rules as well as cash quotes.
Getting a prescription
Erectile dysfunction can be an early sign of heart disease or diabetes, so a first prescription usually comes with a check of blood pressure, blood sugar and cholesterol. A prescription from an in-person or telehealth prescriber can be filled at any pharmacy that has the medicine, which is where comparing cash prices helps.
Questions for your prescriber
- Is it safe with my heart condition and my other medicines?
- Would a daily dose of tadalafil suit me better?
- Which tablet strength gives the right dose, and how do quotes for each compare?
Already have a prescription?
Upload it and licensed pharmacies respond with their own cash price. You choose, and pay the pharmacy.
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Sources
- DailyMed, FDA-approved prescribing information
- MedlinePlus drug information (National Library of Medicine)
- FDA Orange Book (approved generics and therapeutic equivalence)
Written by the Script Unlock editorial team from the sources above. It is general information, not advice for you or your pet; your prescriber decides which medicine is right.
Script Unlock is a marketplace that lets licensed pharmacies quote a cash price on your prescription. It does not prescribe, dispense or sell medication, does not process patient payments, and does not give medical advice. Always follow the instructions of your prescriber and pharmacist and read the medication guide supplied with your medicine.