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How to take Viagra and Cialis correctly, and why they sometimes fail

Written by David Shusterman, MD, board-certified urologist, adapted from his book ED Unlocked. General information, not medical advice for your situation. Who publishes this site.

Viagra (sildenafil), Cialis (tadalafil) and similar pills work only when there is sexual arousal: they strengthen an erection signal your body is already sending, they do not create one. To give them a fair chance, take the dose your prescriber chose, follow the timing and food instructions for your specific drug, give yourself real arousal, and keep alcohol modest. Most "failures" come from one disappointing try, anxiety, or a cause the pill cannot fix. Never combine them with nitrate heart medicines.

What these pills actually do

Sildenafil (Viagra), tadalafil (Cialis), vardenafil and avanafil belong to a class of drugs called PDE5 inhibitors. When you are aroused, nerves release nitric oxide, which relaxes the blood vessels of the penis and lets blood flow in. PDE5 is the enzyme that breaks that signal down. Blocking it lets the signal last longer, so the arteries stay open.

The simplest way to remember it: these pills are amplifiers, not generators. They are a megaphone, not a voice. They need three things to work:

• Actual arousal. A pill will not work on a man sitting at his desk feeling nothing. Touch, attention and a partner who is part of the moment matter.
• Working nerves to carry the signal.
• Reasonably healthy blood vessels to respond to it.

This is why men expecting a chemical on-switch are often disappointed.

It also helps to know where these drugs came from. Sildenafil was developed as a cardiovascular medicine. It relaxes blood vessels, which is why it is also approved for pulmonary hypertension, a disease of the blood vessels in the lungs. Its effect on erections is the same action in a different set of blood vessels.

How to give the pill a fair trial

One disappointing attempt is not a fair trial. Before deciding a pill does not work, go over these points with the person who prescribed it:

• Dose. Was it the dose you were prescribed? Do not raise it on your own.
• Timing. The drugs differ in how long they take to work and how long they last. Ask how to time your specific medicine.
• Food. Some of these drugs are affected by meals more than others. Ask whether yours should be taken on an empty stomach.
• Alcohol. A little may ease nerves for some men, but heavier drinking blunts arousal and works against the pill.
• Arousal and anxiety. Did you have real stimulation? Were you watching yourself, worried about failing?
• Number of attempts. Several tries tell you far more than one.

Do not mix different ED drugs, and never borrow someone else's prescription.

Why anxiety can beat the pill

An erection is something the body allows only when it feels safe. When you panic about losing your erection, your body releases adrenaline. Adrenaline tightens blood vessels fast, and that can override the pill.

That is why a man can take a pill, spend the evening watching himself, and conclude it failed, when the real block was the worry. Removing the pressure, slowing down and talking with your partner outside of the moment often help as much as the medicine.

When a properly used pill still does not work

If the pill gives little or only partial help after a fair trial, the next step is to figure out why, not simply to take more. A urologist will look at which part of the system is limiting you:

• Weak blood flow or a leak. If the erection never gets firm, or fades quickly, the blood vessels or the seal may be the issue. This points toward vascular testing and treatments that act directly on the penis.
• Weak arousal or desire. The problem may be upstream, in the brain or the relationship.
• Hormones. Low testosterone or high prolactin changes the workup. See low testosterone and ED.
• Nerve injury from diabetes or pelvic surgery changes what to expect.
• Performance monitoring, as above, can block real physiology.

If the pills have stopped working because the underlying disease has progressed, other effective options remain, including the vacuum device, penile injections and an implant. See penile injections and implants.

Daily tadalafil: a different use

Some men take a low dose of tadalafil every day instead of on demand. Its purpose can be steady support for blood flow rather than an erection on command. It is also sometimes used for penile rehabilitation, for example after prostate treatment. It is not right for everyone, and the dose and schedule belong to your prescriber.

The safety rules that matter

Never combine with nitrates. If you take nitroglycerin or any other nitrate medicine, including a spray for chest pain, PDE5 inhibitors are off the table. Together they can drop blood pressure dangerously, even fatally.

Get your heart checked. ED can be an early warning sign of heart disease, and sex is exercise. A good prescriber looks at your heart risk first. See ED and heart health.

Be careful with quick online approvals. A sixty-second questionnaire can skip exactly the screening meant to catch a hidden heart problem or a nitrate you did not know you were taking.

Be careful with "natural" boosters. The FDA repeatedly finds sexual enhancement supplements that contain hidden prescription drug ingredients. That is especially dangerous for anyone on nitrates.

Pills also work best on a healthy foundation. Stopping smoking, losing some weight, exercising and sleeping well improve the blood vessels the pill depends on, so the same dose often works better.

ED pills are excellent medicines when they match the cause and are used correctly. If yours are not working, that is information, not a dead end. Talk to a urologist about the next step, and read the full ED treatment options. This article is general information, not medical advice for your situation.

Frequently asked questions

Does Viagra work without arousal?

No. Viagra and similar pills amplify an erection signal that arousal starts; they do not create an erection on their own.

How many times should I try an ED pill before giving up?

One disappointing attempt is not a fair trial. Review dose, timing, food, alcohol and arousal with your prescriber and try several times before deciding it does not work.

Can I take Viagra and Cialis together?

Do not mix ED drugs or change your dose on your own. Any change belongs to your prescriber.

Is it safe to take ED pills with heart medicine?

Many heart medicines are fine, but nitrates such as nitroglycerin are an absolute exception. Tell your prescriber about every medicine you take.

What should I do if ED pills stop working?

See a urologist to find which part of the system is limiting you. Injections, a vacuum device and implants still work when pills do not.