Viagra vs Cialis: 7 Key Differences Explained

Viagra vs Cialis comes down to timing more than strength: in head-to-head trials, sildenafil (Viagra) and tadalafil (Cialis) improve erections about equally, but sildenafil acts for a few hours per dose while tadalafil can help for up to 36 hours and can also be taken as a low daily dose. Food, side effects, other medicines and how often you have sex usually decide which one suits you better.

Source: EAU Guidelines — Management of Erectile Dysfunction; Int Urol Nephrol (PMC) — Direct comparison of tadalafil with sildenafil: systematic review and meta-analysis

Viagra vs Cialis at a glance

Viagra is the brand name of sildenafil, and Cialis is the brand name of tadalafil. Both belong to the same drug class, phosphodiesterase type 5 (PDE5) inhibitors. They do not cause an erection on their own and do not raise sexual desire: they increase blood flow to the penis when you are sexually stimulated.

Both treat erectile dysfunction (ED), and both are also used, under other brand names, for pulmonary arterial hypertension. Tadalafil is additionally approved for the urinary symptoms of benign prostatic hyperplasia (BPH), the non-cancerous enlargement of the prostate. If you are still working out why erections have become difficult, our complete guide to erectile dysfunction covers the causes and tests first.

Sources: MedlinePlus — Sildenafil; MedlinePlus — Tadalafil

Sources: DailyMed (FDA label) — VIAGRA (sildenafil citrate) tablets; DailyMed (FDA label) — CIALIS (tadalafil) tablets

Onset, duration and food: how Viagra vs Cialis differ in timing

How fast each one starts

The Viagra label recommends taking a dose about 1 hour before sex, with a usable window of 30 minutes to 4 hours. On an empty stomach, blood levels peak within 30 to 120 minutes, with a median of about an hour.

Cialis reaches its peak more slowly, at a median of 2 hours, yet many men respond earlier. In one label study, 52% of men taking 20 mg reported a successful erection attempt at or before 30 minutes, compared with 35% on placebo. That is why the label advises taking it at least 30 minutes ahead.

How long each one lasts

Half-life is the time the body needs to clear half of a dose. Sildenafil and its active breakdown product each have a half-life of about 4 hours, so a dose is planned around one sexual episode. Tadalafil’s mean half-life is 17.5 hours, and the Cialis label reports better erections than placebo for up to 36 hours after a single dose.

“Lasting” means the window in which stimulation can produce an erection, not a constant erection.

Sources: DailyMed (FDA label) — VIAGRA (sildenafil citrate) tablets; DailyMed (FDA label) — CIALIS (tadalafil) tablets; EAU Guidelines — Management of Erectile Dysfunction

Food, grapefruit and alcohol

A high-fat meal delays sildenafil’s peak by about 60 minutes on average and lowers the peak level by about 29%, so a heavy dinner right before taking Viagra can make it feel weaker or slower. The NHS gives the practical version: a large meal may make an erection take longer. Tadalafil’s absorption is not influenced by food, so Cialis can be taken with or without a meal.

Grapefruit and grapefruit juice can raise drug levels, so the NHS advises avoiding them with both medicines. Alcohol is the other common issue. The Cialis label notes that about 5 or more units of alcohol together with tadalafil can cause dizziness, a faster heart rate and a drop in blood pressure on standing, and heavy drinking makes erections harder in its own right.

Sources: NHS — Sildenafil: a medicine for erection problems; NHS — Tadalafil; DailyMed (FDA label) — CIALIS (tadalafil) tablets

Doses, daily Cialis and the BPH indication

Sildenafil (Viagra) dosing

The usual starting dose is 50 mg taken as needed, which a doctor can raise to a maximum of 100 mg or lower to 25 mg depending on the effect and side effects. It should not be taken more than once a day. Men over 65 may start at 25 mg because they clear the drug more slowly, and the same lower start is advised alongside certain medicines (see the interactions section).

Tadalafil (Cialis) as needed

For on-demand use, the recommended starting dose is 10 mg before sexual activity, adjusted up to 20 mg or down to 5 mg. Again, the maximum is once a day.

Daily low-dose Cialis

Tadalafil can also be taken every day at the same time, starting at 2.5 mg and increasing to 5 mg if needed. Daily dosing means you do not have to plan sex around a tablet. In a 24-week trial on the Cialis label, the erectile function score improved by 6.1 points with 2.5 mg and 7.0 points with 5 mg, versus 1.2 with placebo. The EAU guidelines state there is no clinically significant difference in effectiveness between daily and on-demand tadalafil, and suggest reviewing periodically whether daily use is still needed.

Tadalafil for an enlarged prostate (BPH)

For BPH symptoms, or for ED and BPH together, the dose is 5 mg once daily. In a 12-week label trial, the International Prostate Symptom Score (IPSS) fell by 4.8 points with tadalafil compared with 2.2 with placebo. The EAU describes tadalafil 5 mg as the only drug licensed for both ED and lower urinary tract symptoms, which makes it a practical single tablet for men with both problems. Sildenafil does not have this indication.

Sources: DailyMed (FDA label) — VIAGRA (sildenafil citrate) tablets; DailyMed (FDA label) — CIALIS (tadalafil) tablets; EAU Guidelines — Management of Erectile Dysfunction

Viagra vs Cialis side effects

Both drugs commonly cause headache, flushing, a stuffy nose and indigestion, usually mild and short-lived. The pattern differs in two noticeable ways.

Visual changes with sildenafil

The Viagra label describes visual disturbances as mild to moderate and temporary, mainly a color tinge to vision; some men notice light sensitivity or blurred vision. These effects rise with the dose: abnormal vision was reported by 1%, 2% and 11% of men on 25, 50 and 100 mg, versus 1% on placebo. MedlinePlus describes the typical complaint as objects looking blue-tinted.

Back pain and muscle aches with tadalafil

With on-demand Cialis 10 or 20 mg, back pain affected 5–6% of men (3% on placebo) and muscle aches (myalgia) 3–4% (1% on placebo). These aches usually begin 12 to 24 hours after a dose and settle within 48 hours; only about 0.5% of men stopped treatment because of them.

The head-to-head meta-analysis confirmed this trade-off: flushing was less common with tadalafil, while back pain and myalgia were more common.

Sources: DailyMed (FDA label) — VIAGRA (sildenafil citrate) tablets; DailyMed (FDA label) — CIALIS (tadalafil) tablets; MedlinePlus — Sildenafil; Int Urol Nephrol (PMC) — Direct comparison of tadalafil with sildenafil: systematic review and meta-analysis

Rare but serious effects

Both medicines carry the same rare warnings: sudden loss or blurring of vision, sudden hearing loss (sometimes with ringing or dizziness), chest pain during sex, and an erection lasting more than 4 hours. Each of these needs urgent medical care, and you should not take further doses until a doctor has assessed you.

Sources: MedlinePlus — Sildenafil; MedlinePlus — Tadalafil

Contraindications and drug interactions

Absolute no-gos: nitrates and riociguat

Neither drug may be used with any form of organic nitrate, such as nitroglycerin (GTN) sprays or isosorbide tablets for angina, or with recreational “poppers” (amyl nitrite). The combination can drop blood pressure dangerously. The EAU calls this an absolute contraindication and also lists nicorandil. Both labels also contraindicate guanylate cyclase stimulators such as riociguat, a lung blood-pressure drug.

Because of tadalafil’s long half-life, the Cialis label says that if nitrates become medically necessary, at least 48 hours should pass after the last dose, with close hospital monitoring. Always tell emergency staff which ED medicine you took and when.

Sources: EAU Guidelines — Management of Erectile Dysfunction; DailyMed (FDA label) — CIALIS (tadalafil) tablets; DailyMed (FDA label) — VIAGRA (sildenafil citrate) tablets

Alpha-blockers

Alpha-blockers (such as tamsulosin or doxazosin, used for prostate symptoms or blood pressure) also lower blood pressure. For ED, both labels ask that you be stable on the alpha-blocker first; Viagra should then start at 25 mg and Cialis at its lowest recommended dose. For BPH, the Cialis label does not recommend combining daily tadalafil with an alpha-blocker and advises stopping the alpha-blocker at least one day before starting.

CYP3A4 inhibitors and other medicines

Both drugs are broken down by the liver enzyme CYP3A4. Strong blockers of this enzyme, such as ketoconazole, itraconazole and HIV protease inhibitors like ritonavir, raise blood levels sharply; ritonavir increases sildenafil exposure about 11-fold. With ritonavir, the Viagra label limits the dose to 25 mg in any 48-hour period. For Cialis with strong CYP3A4 inhibitors, the limits are 10 mg no more than once every 72 hours for on-demand use, or 2.5 mg for daily use.

Other medicines can also interact, including rifampin, carbamazepine, phenytoin, cimetidine and St. John’s wort. Never take two PDE5 inhibitors together, and give your doctor a full list of prescriptions and supplements.

Sources: DailyMed (FDA label) — VIAGRA (sildenafil citrate) tablets; DailyMed (FDA label) — CIALIS (tadalafil) tablets; MedlinePlus — Sildenafil; MedlinePlus — Tadalafil

Which works better? Efficacy and preference studies

On erection quality, the honest answer in the Viagra vs Cialis debate is “about the same.” The EAU guidelines state that no differences in treatment efficacy have been demonstrated among PDE5 inhibitors. A 2017 systematic review pooled 16 head-to-head trials and 5,189 patients and found no significant difference in erectile function scores, intercourse satisfaction or overall satisfaction between tadalafil and sildenafil.

Preference is where they diverge. In the same meta-analysis, both men and their partners preferred tadalafil, and tadalafil improved psychological measures such as sexual confidence; the likely reason is the longer window, which takes the stopwatch out of sex. In an open-label crossover trial in China, 350 men tried 20 mg tadalafil and 100 mg sildenafil in turn: 69.1% chose tadalafil for the extension phase, even though erectile function improved almost identically (12.03 vs 11.86 points).

Read these results with caution: the meta-analysis authors reported high heterogeneity and quality limitations, and the crossover trial was funded and run by tadalafil’s manufacturer. A man who has sex occasionally and wants the shortest exposure may still prefer sildenafil.

Sources: EAU Guidelines — Management of Erectile Dysfunction; Int Urol Nephrol (PMC) — Direct comparison of tadalafil with sildenafil: systematic review and meta-analysis; Asian J Androl (PMC) — Randomized crossover study comparing sildenafil and tadalafil in Chinese men

Brand vs generic, cost and buying safely

Generic sildenafil and generic tadalafil contain the same active ingredient as Viagra and Cialis. The FDA requires a generic to have the same active ingredient, strength and dosage form as the brand and to be made under the same strict manufacturing standards, and notes that generics tend to cost less than their brand-name counterparts.

Prices vary by country, pharmacy, insurance and dose, so we do not quote figures. Note that daily tadalafil means a tablet every day, while on-demand use means paying only for the doses you take.

Be careful with “herbal” or online sexual-enhancement products. The FDA warns that many such products are likely to contain dangerous hidden drug ingredients and can lead to serious health problems and hospitalization. In the UK, the NHS notes that a pharmacist can sell sildenafil or tadalafil after a consultation, but advises seeing a doctor within 6 months because erection problems can be a sign of conditions like diabetes or heart disease.

Sources: FDA — Generic Drug Facts; FDA — Sexual Enhancement and Energy Product Notifications; NHS — Tadalafil

How to choose between Viagra vs Cialis

The EAU suggests basing the choice on how often you have sex and your own experience with the drugs. It notes that men who prioritize efficacy may start with sildenafil 50 mg, while men who prioritize tolerability may start with tadalafil 10 mg. In practice, these situations tend to point one way or the other:

• Sildenafil may suit you if you have sex occasionally, can plan about an hour ahead, prefer the drug to leave your system within hours, or got back pain from tadalafil.
• Tadalafil may suit you if you want spontaneity over a weekend, often eat before sex, have sex several times a week (daily 5 mg), or also have urinary symptoms from an enlarged prostate.
• Either needs extra care if you take alpha-blockers, strong CYP3A4 inhibitors or have heart, liver or kidney disease; a doctor will adjust the dose.

If the first drug disappoints, check the basics first: dose, timing, sexual stimulation, a heavy meal or alcohol. A doctor can then adjust the dose or switch, and look for an underlying cause. When tablets fail despite proper use, other options exist, including a penile prosthesis.

Source: EAU Guidelines — Management of Erectile Dysfunction

What about vardenafil and avanafil?

Two other PDE5 inhibitors are available in many countries. Vardenafil has a half-life of about 3.9 hours, similar to sildenafil, and works from about 30 minutes, with roughly one in three men getting a satisfactory erection within 15 minutes in trials. Avanafil is the fastest to peak, at about 30 to 45 minutes, and is recommended 15 to 30 minutes before sex. Like sildenafil, both can be delayed by high-fat meals, and the same nitrate rules apply.

Source: EAU Guidelines — Management of Erectile Dysfunction

When to see a doctor

ED tablets should follow a medical check, not replace one, because erection problems can be an early sign of diabetes or heart disease. Book a review if you have not had one, if a tablet does not work after several attempts at the right dose, or if side effects bother you. Seek urgent care for:

• An erection lasting more than 4 hours (priapism).
• Sudden loss of vision in one or both eyes, or sudden hearing loss.
• Chest pain, fainting or severe dizziness during or after sex; do not use nitrates if you have taken an ED drug unless doctors know about it.
• Swelling of the face or throat, hives or trouble breathing after a dose.

Sources: MedlinePlus — Tadalafil; NHS — Sildenafil: a medicine for erection problems

If you would like help choosing between tablets or exploring what comes next, you can arrange a confidential consultation with our urologist-andrologist, Assoc. Prof. Dr. Zülfü Sertkaya, by WhatsApp. Read more about our erectile dysfunction treatment options, from medication plans to surgery.

FAQs about Viagra vs Cialis

Is Cialis stronger than Viagra?

No. At their standard doses, the two work about equally well. A meta-analysis of 16 head-to-head trials found no significant difference in erectile function scores between tadalafil and sildenafil. Cialis feels “stronger” to some men because its effect window is much longer, not because erections are firmer. Dose and correct use matter more than the brand you choose.

Source: Int Urol Nephrol (PMC) — Direct comparison of tadalafil with sildenafil: systematic review and meta-analysis

Can I take Viagra and Cialis together?

No. Combining two PDE5 inhibitors adds their blood-pressure-lowering effects and their side effects without a proven benefit for most men. MedlinePlus advises against taking sildenafil with other PDE5 products, and the same applies to tadalafil. If one drug is not working well enough, talk to your doctor about adjusting the dose or switching rather than stacking tablets.

Source: MedlinePlus — Sildenafil

Which is better for men with an enlarged prostate?

Tadalafil, because it is the only one of the two approved for BPH symptoms. A 5 mg daily dose treats both erectile dysfunction and urinary symptoms such as a weak stream or frequent urination. In a 12-week trial, prostate symptom scores improved by 4.8 points versus 2.2 with placebo. Avoid combining it with an alpha-blocker for BPH unless your doctor directs otherwise.

Source: DailyMed (FDA label) — CIALIS (tadalafil) tablets

Why does Cialis give some men back pain?

Back pain and muscle aches are recognized tadalafil side effects, reported by about 5–6% and 3–4% of men on on-demand doses. They typically start 12 to 24 hours after the tablet and resolve within 48 hours. The exact mechanism is not explained on the label. If the pain is troublesome, sildenafil is a reasonable alternative to discuss.

Source: DailyMed (FDA label) — CIALIS (tadalafil) tablets

Is daily Cialis better than taking it as needed?

Not in terms of effectiveness. The EAU guidelines report no clinically significant difference between once-daily and on-demand tadalafil. Daily 2.5–5 mg suits men who have sex often, want spontaneity or also have prostate symptoms. On-demand dosing suits men who have sex less often and prefer fewer tablets. The need for daily treatment should be reviewed periodically.

Source: EAU Guidelines — Management of Erectile Dysfunction

Are generic sildenafil and tadalafil as good as the brands?

Approved generics must contain the same active ingredient in the same strength and dosage form as the brand and meet the same manufacturing standards, according to the FDA, and they usually cost less. The risk lies in unregulated online or “natural” products, which the FDA warns may contain hidden drug ingredients. Buy only from a licensed pharmacy with a prescription.

Source: FDA — Generic Drug Facts