Sildenafil vs Tadalafil (Viagra vs Cialis): Which ED Pill Is Right for You?

Written by Cherlie Joseph, MSN, FNP-BC · Medically reviewed by Naurah Gaspard, DNP, FNP-C, FNP-BC · Updated November 2026

Sildenafil (Viagra) and tadalafil (Cialis) work the same way and are both effective for erectile dysfunction. The main difference is timing: sildenafil is taken shortly before sex and lasts several hours, while tadalafil can work for up to 36 hours and can also be taken once a day. Neither is safe with nitrate heart medicines.

How sildenafil and tadalafil work

Both are PDE5 inhibitors. They relax the smooth muscle in the penis's blood vessels so more blood can flow in when you are sexually aroused. They do not cause an erection on their own and they do not raise sex drive. Both are available as lower-cost generics, and the AUA guideline lists PDE5 inhibitors as a standard first option for ED in men who can safely take them.

Side-by-side comparison

	Sildenafil (Viagra)	Tadalafil (Cialis)
How you take it	As needed, about 1 hour before sex (label allows 30 minutes to 4 hours)	As needed before sex, or a low dose once daily
How long it can work	About 4 to 6 hours	Up to 36 hours
Food	A heavy, high-fat meal can delay it	Not much affected by food
Common side effects	Headache, flushing, stuffy nose, indigestion, a blue tint or light sensitivity in vision	Headache, flushing, stuffy nose, indigestion, back or muscle aches
Other approved uses	Pulmonary arterial hypertension (as Revatio)	Enlarged prostate (BPH) symptoms; pulmonary arterial hypertension (as Adcirca)
Generic available	Yes	Yes

Follow the dose and timing on your prescription label. Neither medicine should be taken more than once in 24 hours unless your prescriber has specifically set up a daily tadalafil plan.

Which one might fit you better?

There is no single “best” ED pill. Studies show both work well, so the choice usually comes down to lifestyle, side effects and health history:

• Sildenafil may suit people who have sex less often and prefer a shorter-acting medicine they take only when needed.
• Tadalafil may suit people who want more spontaneity, such as a weekend window, or who also have urinary symptoms from an enlarged prostate, since daily tadalafil is approved for both.
• If one causes bothersome side effects or does not work after several tries at the right dose and timing, switching to the other is reasonable to discuss.

A common reason these pills “don't work” is how they are taken: too soon before sex, after a big meal (for sildenafil), without arousal, or after only one or two attempts.

Safety: who should not take them

Both medicines lower blood pressure a little. That becomes dangerous with certain other drugs. According to the FDA labels summarized by MedlinePlus:

• Never combine with nitrates such as nitroglycerin tablets or spray, isosorbide mononitrate or dinitrate, or recreational “poppers.” Blood pressure can drop to a dangerous level.
• Do not combine with riociguat (Adempas), a lung blood pressure medicine.
• Use caution with alpha-blockers (such as tamsulosin or doxazosin) and with some blood pressure medicines; your prescriber may adjust timing or dose.
• Some HIV medicines, antifungals and antibiotics raise blood levels of these drugs.
• Tell your provider about heart disease, a recent heart attack or stroke, very low or uncontrolled blood pressure, kidney or liver disease, or eye conditions.

Because sex is a form of physical activity, your provider will also ask whether you can exercise without chest pain or breathlessness. If not, a heart evaluation comes first.

Cost and where to get them

Generic sildenafil and tadalafil are usually far cheaper than the brand names, but prices vary widely by pharmacy, dose and quantity, and they change often. Compare prices with a pharmacy discount tool such as GoodRx, ask your pharmacist for the cash price, or check whether your insurance covers ED medicine. Avoid websites that sell ED pills without a prescription and “male enhancement” supplements; the FDA has repeatedly found hidden drug ingredients in these products.

If you are already prescribed one of these medicines and need a refill, a nurse practitioner licensed in your state at OurTopClinic can review your history and decide whether continuing is appropriate. If ED is new for you, start with a visit so the cause can be looked at too.

Frequently asked questions

Is Cialis stronger than Viagra?

Not really. Both work about equally well for most men. Tadalafil (Cialis) lasts longer, up to 36 hours, while sildenafil (Viagra) works for about 4 to 6 hours. Longer-lasting is not the same as stronger.

Can I take sildenafil and tadalafil together?

No. Taking two PDE5 inhibitors together increases the risk of low blood pressure and side effects without a proven benefit. Use only the medicine and schedule your prescriber gave you.

Can I drink alcohol with ED pills?

A small amount is usually fine for most people, but heavy drinking can make ED worse and adds to the blood-pressure-lowering effect, which can cause dizziness, a fast heartbeat or headache.

Sources

• MedlinePlus: Sildenafil drug information
• MedlinePlus: Tadalafil drug information
• Burnett AL et al. Erectile Dysfunction: AUA Guideline (Journal of Urology, 2018)

Keep reading

• ED causes: why erectile dysfunction happens
• ED treatment online in Florida: how it works
• Generic vs brand medications
• Ways to save on medication costs
• Browse all conditions and treatments A to Z

This article is for general education and is not a substitute for medical advice. Treatment, including any prescription, is decided by a licensed provider after reviewing your health history. OurTopClinic is not for emergencies; if you have a medical emergency, call 911. OurTopClinic serves adults located in Florida, New Mexico, Oregon and Washington. Learn more at ourtopclinic.com.