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Is sildenafil safe? For most men, sildenafil (Viagra®) is a safe and effective treatment for ED (erectile dysfunction) when used as prescribed. However, like all medications, it comes with potential side effects and drug interactions.
Most adverse effects are mild and temporary. For some, especially those with preexisting medical conditions, sildenafil can cause more serious side effects.
We’ll break down how sildenafil works for treating ED, who shouldn’t take it, and how to ensure you’re using it safely to improve your sex life.
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In the ’80s, researchers tested a medication called sildenafil citrate for treating high blood pressure (hypertension) and angina (chest pain). While the treatment appeared promising for these purposes, it was more potent in — ahem — another more sensitive area of the body.
Apparently, many of the participants were embarrassed to disclose to the research staff that they were experiencing erections during the trial.
Though sildenafil was intended to relax and dilate blood vessels around the heart, it’s also active in the blood vessels around the penis — which is how it supports erections. Talk about getting more than you bargained for.
Needless to say, researchers took an unexpected pivot and decided to investigate sildenafil as a treatment for erectile dysfunction. After all, if it was causing erections among men who weren’t necessarily looking for that effect — imagine what it could do for those struggling to stay hard.
After further trials, sildenafil citrate was approved by the U.S. Food and Drug Administration (FDA) in 1998. It’s the active ingredient in brand-name Viagra, now a very well-known drug for ED.
Treating ED is the most common use for Viagra. Sildenafil is also used in different dosages to treat pulmonary arterial hypertension under the brand name Revatio®.
Sildenafil is in a class of drugs called phosphodiesterase 5 inhibitors (PDE5 inhibitors), along with other meds like Cialis® (tadalafil), Stendra® (avanafil), and Levitra® (vardenafil).
These are the gold-standard drugs for the treatment of erectile dysfunction. Studies show that just one dose of Viagra has a 70 to 80 percent success rate for treating ED.
PDE5 is an enzyme that regulates blood flow to many parts of the body, including the soft erectile tissues inside the penis. It can keep the smooth muscle in the arteries supplying the penis from relaxing, which can reduce blood flow.
PDE5 inhibitors increase blood flow to your penis, resulting in longer, harder erections when you experience sexual stimulation.
Your next question is probably when it’ll start working and how long sildenafil lasts. We get it — this is important stuff when planning the logistics of your evening.
Most of the time, Viagra begins to work 30 to 60 minutes after taking it.
It may work more slowly if you take it after eating a fatty meal (like a burger and fries), so make sure you strategically pop that little blue pill based on your plans.
As for how long it lasts, the packaging insert says Viagra has a half-life of four hours.
No, this doesn’t mean you’re still going to have a hard-on at that point. It just means the drug will still be in your system but not necessarily at a high enough concentration to have noticeable effects.
For the best results, plan to have sex within these first four hours of taking sildenafil.
When used as directed to treat erectile dysfunction, sildenafil is safe and effective for most men. However, like any drug, it has potential side effects and drug interactions to consider.
The most common sildenafil side effects include:
Headaches, affecting up to 28 percent of men who use it
Muscle aches and back pain
Nasal congestion due to its dilating effects on blood vessels
Lightheadedness or dizziness
Flushing of the skin (like red cheeks)
Heartburn or indigestion
Nausea, though this is only reported by a small percentage of men who use it
Reduced blood pressure when combined with certain other medications
Blurred vision or otherwise abnormal vision, though this is usually mild and temporary
If you take a dose of sildenafil above 100 milligrams (mg), you’ll have a higher risk of experiencing any of these side effects.
Other more serious but less common side effects of Viagra have also been reported, such as:
Priapism, a prolonged erection that lasts several hours and can become painful
Sudden hearing loss
Rare permanent loss of vision due to optic nerve damage (known as what is non-arteritic anterior ischemic optic neuropathy)
If you experience any of these potentially serious side effects, seek immediate medical attention.
If your sildenafil side effects are severe (or even if they just impact your life too much), your provider may recommend an alternative drug or another ED treatment.
Sildenafil acts on the blood vessels in your penis, so you may wonder if it has any worrisome effects on your cardiovascular system as a whole.
There have been reports of stroke, heart attack, and irregular heartbeats among those who take Viagra. However, there’s currently no solid evidence directly linking sildenafil to heart attacks in men.
The fact is, people with ED have a higher likelihood of having heart disease — and vice versa. For example, problems with both your penis and your heart can be associated with a vascular condition affecting blood flow.
PDE5 inhibitors like sildenafil may not be safe for folks who have existing heart problems. It’s unclear if it is safe for those who’ve had a heart attack, stroke, or irregular heartbeat within the last six months. Talk to your healthcare provider if you have abnormal blood pressure at rest or a history of heart failure or unstable angina.
As a vasodilator, sildenafil widens blood vessels throughout your entire body — which is to say, areas other than your penis. So it may actually lower blood pressure. This drop is generally so small that most men don’t notice it, even those taking medication for high blood pressure.
Still, a drop in blood pressure can be dangerous — even life-threatening — if you have existing heart-related concerns.
Additionally, sildenafil can interact with drugs called nitrates, which are commonly prescribed for heart conditions. We’ll discuss this more next.
Finally, 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.
Certain types of medications shouldn’t be taken with sildenafil due to potentially serious interactions, like:
Nitrates (such as nitroglycerin, isosorbide dinitrate, or isosorbide mononitrate) used to treat congestive heart failure and chest pain
Alpha-blockers, which are prescribed for hypertension and benign prostatic hyperplasia (BPH)
Recreational drugs called “poppers,” which may contain nitrites
Ketoconazole, a drug used to treat fungal infections
When nitrate-containing drugs are used with sildenafil, they can cause a sudden and severe drop in blood pressure. This may make you feel dizzy or (more seriously) could cause you to pass out.
Ketoconazole can inhibit certain proteins in your liver. This can result in higher-than-normal levels of sildenafil in your body, which may lead to headaches, flushing, and dizziness.
Sildenafil can even potentially trigger a heart attack or stroke when combined with certain other medications.
The best way to avoid adverse effects is to disclose all your prescription, over-the-counter, and recreational drug use to your healthcare provider before you begin using Viagra.
Additionally, certain preexisting medical conditions may increase your risk of experiencing side effects from using sildenafil. Let your provider know if you have:
A deformed penis shape or condition called Peyronie’s disease (characterized by a curved penis)
Heart issues or have previously had a stroke or heart attack
Blood cell-related conditions, such as multiple myeloma, sickle cell anemia, or leukemia
High blood pressure, low blood pressure, or pulmonary arterial hypertension (PAH)
An eye-related condition like retinitis pigmentosa, which can increase your risk of other vision problems when using ED medications
Bleeding problems or stomach ulcers
Liver and kidney problems, including being on dialysis
Sildenafil isn’t suitable for everyone. To ensure it’s safe for you, be open with your medical provider about your health history.
Dealing with ED can understandably trigger a range of emotions. Frustration, anxiety, depression, and shame can impact your quality of life.
It might be tempting to throw caution to the wind and try anything just to regain control. However, you’re wise to go over your situation with a professional and understand your options.
Sildenafil is highly effective and safe when used as directed, but that doesn’t mean you should disregard potential risks.
To reduce your risk of side effects and dangerous drug interactions, adhere to the following tips for how to take Viagra for best results:
Take it as prescribed. Sildenafil is most commonly prescribed in once-daily doses between 25 and 100 milligrams for ED. Your healthcare provider will determine the best dosage based on various factors — more doesn’t necessarily equal better.
Use it strategically. Sildenafil is most effective when taken at least 30 minutes to one hour before sex. For most people, it can provide ED relief for around four hours. Take this into account when planning to use sildenafil for sex.
Know the potential side effects of sildenafil. Sildenafil isn’t for everyone. It can interact with other medications and put your health at risk. It may also lead to side effects, like dizziness, prolonged erection, or visual changes.
Communicate with your provider. We know how awkward it can be to talk about your sexual activity with, well, most people. Still, make sure your healthcare provider is aware of any preexisting health conditions you have, as well as any supplements or drugs you use.
If you’re unsure how to take sildenafil properly or whether it’s even right for you, consider talking to a healthcare professional online for medical advice.
Is Viagra safe? Yes, sildenafil and brand-name Viagra are usually a safe and effective drug for ED management when taken as prescribed.
Just keep the following things in mind if you’re considering using sildenafil to improve your sex life:
Understand the potential side effects. Viagra can cause side effects, interact with other medications, and be dangerous for those with certain health conditions. Speak openly with your healthcare provider about your lifestyle and health history before starting Viagra or any other erectile dysfunction medication.
Know there are other options. In some cases, another ED drug — such as tadalafil or avanafil — may be a better fit for you. Alternatively, you might be interested in Hims hard mints, chewable ED meds containing the same active ingredients as other ED prescriptions in personalized dosages.
Identify other factors that may be causing ED. ED affects an estimated 30 million men in the U.S. alone, and many experience psychological ED. This is when things like depression, anxiety, or sexual performance anxiety get in the way of your erections.
ED can be frustrating for everyone involved. Fortunately, living with ED doesn’t need to be a life sentence.
Take our free virtual sexual health assessment to start exploring your treatment options.
Hims & Hers has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references. See a mistake? Let us know at [email protected]!
This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.
Bachelor of Arts, Egyptian and Ancient Western Asian Archaeology - Brown University | College, 2011
Doctor of Medicine - Brown University | Warren Alpert Medical School, 2017
Master of Public Health - Columbia University | Mailman School of Public Health, 2018
Master of Liberal Arts, Journalism - Harvard University | Harvard Extension School, 2022
Master of Science, Healthcare Leadership - Cornell University | Weill Cornell Graduate School of Medical Sciences, 2024
Master of Business Administration - Cornell University | Samuel Curtis Johnson Graduate School of Management, 2024
Internship - NYU Grossman School of Medicine | Internal Medicine Residency—Community Health Track, 2019
New York, 2019
Certified in Public Health - National Board of Public Health Examiners, 2018
Medical Writer Certified - American Medical Writers Association, 2020
Editor in the Life Sciences - Board of Editors in the Life Sciences, 2020
Certified Personal Trainer - National Academy of Sports Medicine, 2022
Certified Nutrition Coach - National Academy of Sports Medicine, 2023
Board Certified Medical Affairs Specialist - Accreditation Council for Medical Affairs, 2023
Certificate of Advanced Education in Obesity Medicine - Obesity Medicine Association, 2025
Regulatory Affairs Certification - Regulatory Affairs Professionals Society, 2025
General Practice
Medical Expert Board Member - Eat This, Not That!, 2021–
Director Scientific & Medical Content - Stealth Biotech PBC, 2023–2024
Director, Medical Content & Education - Ro, 2021–2023
Associate Director, Medical Content & Education - Ro, 2020–2021
Senior Medical Writer - Ro, 2019–2020
Medical Editor/Writer - Sharecare, 2017–2020
Medical Student Producer - The Dr. Oz Show, 2015–2016
Research Affiliate - University Hospitals of Cleveland, 2013–2014
Title: Biomechanical evaluation of a novel suturing scheme for grafting load-bearing collagen scaffolds for rotator cuff repair
Published in: Clinical Biomechanics
Date: 2015
URL: https://www.clinbiomech.com/article/S0268-0033(15)00143-6/abstract
Title: Pelvic incidence and acetabular version in slipped capital femoral epiphysis
Published in: Journal of Pediatric Orthopaedics
Date: 2015
Title: Relationship between pelvic incidence and osteoarthritis of the hip
Published in: Bone & Joint Research
Date: 2016
URL: https://boneandjoint.org.uk/Article/10.1302/2046-3758.52.2000552
Title: Effects of PDGF-BB delivery from heparinized collagen sutures on the healing of lacerated chicken flexor tendon in vivo
Published in: Acta Biomaterialia
Date: 2017
URL: https://www.sciencedirect.com/science/article/pii/S1742706117305652
Dr. Bohl’s medical expertise is regularly featured in consumer health media:
Eat This, Not That!: Contributor and Medical Expert Board Member on nutrition and wellness topics
The Dr. Oz Show: Behind-the-scenes contributor to Emmy Award-winning health segments
Sharecare: Public-facing health writer, simplifying complex medical issues for millions of readers
Dr. Bohl developed a passion for medical content while working at The Dr. Oz Show. He realized that, through the media, he could bring important health information to the lives of many more people than he would be able to working in a doctor’s office.
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