Medically reviewed by Kristin Hall, FNP
Written by Our Editorial Team
Last updated 9/7/2021
Sildenafil, the active ingredient in Viagra®, is one of the most effective and popular treatments for erectile dysfunction, or ED.
As a PDE5 inhibitor, sildenafil works by increasing blood flow to the erectile tissue inside your penis, making it easier to get and maintain an erection.
Research shows that it’s effective, and it’s used by millions of men on a regular basis to treat ED.
If you’ve ever looked into using sildenafil, you may have wondered whether it’s safe to use for the long term.
For most men, sildenafil is a safe option for treating ED. However, like all medications, it does have the potential to produce side effects and interactions with other drugs that you should be aware of before using it.
Below, we’ve discussed how sildenafil works as a treatment for erectile dysfunction, as well as the side effects and drug interactions that it can cause.
We’ve also answered a few frequently asked questions about the safety of sildenafil and other medications for ED.
As a treatment for ED, sildenafil works by inhibiting the effects of the phosphodiesterase type 5 enzyme, or PDE5.
PDE5 is found inside the smooth muscle cell of certain blood vessels. It plays an important role in regulating blood flow to many parts of your body, including the soft erectile tissue inside your penis.
To understand how sildenafil treats ED, it’s important to understand the basics of how erections happen in the first place.
Erections require mental or physical sexual stimulation. When you feel sexually aroused, your nervous system causes the muscles of your penis to relax, allowing blood to flow into the erectile tissue inside your penis.
As blood flows into this tissue, your penis becomes larger and firmer. To maintain your erection, a fibrous membrane called the tunica albuginea contracts, trapping the blood inside your penis and allowing you to stay hard during sex.
By inhibiting the action of PDE5, sildenafil improves blood flow to your penis, making it easier to get and maintain an erection when you’re sexually aroused.
Other popular medications for ED, such as tadalafil (the active ingredient in Cialis®), vardenafil (Levitra®) and avanafil (Stendra®) also work by inhibiting PDE5 and improving blood flow to the penis.
Contrary to popular belief, erectile dysfunction medications don’t have any effect on sexual arousal or your level of interest in sex.
They also won’t cause you to develop an erection on their own. Instead, they just make it easier to get an erection when you’re already in the mood for sex.
Like other medications, sildenafil can potentially cause side effects. The FDA lists the following common adverse effects for Viagra, a common brand of sildenafil citrate:
Myalgia (muscle aches and pain)
Sildenafil is prescribed in several dosages, from 25 to 100mg. Most side effects become more common at higher doses of sildenafil, with men prescribed the lowest 25mg dose of sildenafil reporting the lowest rates of side effects.
In clinical trials, headache and flushing were by far the most common side effects of sildenafil, reported by 16 to 28 percent and 10 to 18 percent of users respectively.
Although uncommon, sildenafil may cause more severe side effects. Make sure to contact your healthcare provider or seek immediate medical help if you experience any of the following side effects:
Sudden severe loss of vision
Sudden loss of hearing, or decrease in hearing sensitivity
Painful erection that lasts for four hours or longer
Ringing in your ears
Dizziness, lightheadedness or fainting
Shortness of breath
Itching or burning while you urinate
While these side effects may sound worrying, it’s important to keep them in context. Most guys who use sildenafil for erectile dysfunction (and other ED medications) only develop mild side effects, with serious issues like priapism (a potentially painful, prolonged erection lasting longer than four hours) highly uncommon.
It’s also important to keep in mind that most ED medications only stay in your system for a few hours at a time.
This means that even if you do develop side effects after taking sildenafil, they usually won’t be long-lasting.
Sildenafil is a safe medication when it’s used as directed. Tens of millions of men of all ages and backgrounds use it and similar ED medications on a regular basis, with serious side effects very uncommon.
Although sildenafil is a safe medication when it’s used as directed, it has the potential to interact with certain other medications. In some cases, these interactions may be dangerous.
For example, sildenafil and other ED medications can interact with nitrates, alpha blockers and other medications used to treat high blood pressure and heart disease.
When these medications are used together, they can cause a sudden, severe decrease in blood pressure that may result in dizziness, fainting, or lead to serious, life-threatening cardiovascular events such as heart attack or stroke.
Some recreational drugs, such as poppers (alkyl nitrites) can also cause dangerous interactions when used with sildenafil or other medications for ED.
Our guide to common sildenafil interactions provides more information on medications to avoid while using sildenafil or other ED medications.
One common myth about sildenafil is that it can damage the cardiovascular system and cause serious medical emergencies such as heart attack or stroke.
Currently, there’s no conclusive scientific evidence that links sildenafil or other ED medications to heart attacks in men.
For more information, read our blog on Can Viagra Cause a Heart Attack?
A heart attack, or myocardial infarction, occurs when the supply of blood to the heart is abruptly blocked.
It’s usually caused by coronary artery disease — a form of heart disease that involves the buildup of plaque inside the walls of the arteries that supply blood to your heart.
As a vasodilator, sildenafil actually increases blood flow throughout your body, including to areas other than your penis.
For example, sildenafil is also used to treat pulmonary arterial hypertension, or PAH — a form of high blood pressure that can affect the blood vessels in the lungs.
The FDA recommends that people with a history of heart problems, such as heart attack, chest pain, irregular heartbeat, angina, heart failure or aortic stenosis, apply caution before using any medication to treat ED.
If you currently have a heart problem or have previously had any type of cardiovascular health problem, it’s important to inform your healthcare provider before using sildenafil.
It’s also important to be aware that sexual activity of any type can put a strain on your heart. If you have an existing heart condition, the physical stress of having sex may increase your risk of heart attack, stroke or other cardiovascular events.
It’s important to discuss this with your healthcare provider before taking sildenafil, or if you have any concerns about your cardiovascular health and ability to handle the physical strain of having sex.
Another popular ED myth is that using drugs like sildenafil can worsen your erectile dysfunction, causing you to become dependent on medication.
As we’ve discussed in more detail in our guide to Viagra dependence, sildenafil isn’t a physically addictive drug.
Other widely-used ED medications, such as tadalafil, vardenafil and avanafil, are also physically non-addictive.
There’s also no evidence that sildenafil is psychologically addictive. When sildenafil is used as it should be — that is, at the prescribed dose, as needed to treat ED — it’s a safe, effective drug for improving erections and sexual performance.
Sildenafil is a safe and effective medication when it’s used as directed. Make sure to follow the tips listed below to use sildenafil safely to treat erectile dysfunction:
Don’t exceed the recommended dose. Sildenafil is prescribed in three common doses, from 25mg to a maximum dose of 100mg. Make sure to only use the amount of sildenafil that’s prescribed by your healthcare provider.
Take sildenafil one hour before sex. Sildenafil is most effective when it’s used around one hour before sex.
Most of the time, a typical dose of sildenafil will provide relief from ED for about four hours.
Use sildenafil once a day. Sildenafil is designed for use as-needed, up to one time per day.
Other ED medications, such as tadalafil, offer longer-lasting effects and may be a more suitable choice if you want to have sex more than one time per 24 hours.
Inform your healthcare provider about preexisting conditions. If you’re affected by any medical conditions, or if you use other prescription medications, it’s important to let your healthcare provider know before using sildenafil.
Limit your alcohol consumption. Drinking alcohol, especially in excess, can increase your risk of developing side effects from sildenafil. Try to limit your alcohol consumption and drink within your limits.
Avoid herbal, over-the-counter ED treatments. These products often contain unsafe, unlabeled ingredients. Instead, stick to FDA-approved medications for ED like sildenafil, tadalafil and others.
Let your healthcare provider know if sildenafil isn’t effective. People’s responses to sildenafil and other ED medications can vary. If you don’t experience any improvements after using sildenafil, let your healthcare provider know.
When it’s used as directed, sildenafil is one of the safest and most effective ED medications on the market.
However, it’s important to use sildenafil responsibly. This means sticking with the dosage you’re prescribed and informing your healthcare provider if you have any preexisting conditions or use other prescription medications.
Ready to stop erectile dysfunction for good? Our full range of ED medications features proven, science-based options for dealing with erectile dysfunction such as sildenafil, tadalafil and new ED treatments such as Stendra.