Sildenafil 100 mg dose: uses, side effects, and more

Reviewed by Chimene Richa, MD, 

Written by Michael Martin 

Reviewed by Chimene Richa, MD, 

Written by Michael Martin 

last updated: Dec 13, 2021

6 min read

With some things in life, more is better. But this isn’t necessarily true when it comes to medication. The maximum dose you can take of sildenafil (brand name Viagra) per day is 100 mg, and it’s not the best dose for everyone. Read on to learn more about the uses and side effects of sildenafil 100 mg. 

Viagra Important Safety Information: Read more about serious warnings and safety info.

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Is sildenafil 100 mg safe?

Sildenafil citrate is the generic form of Viagra, a.k.a. "the little blue pill," an oral medication used to treat erectile dysfunction (ED). It's also sold under the brand name Revatio, which is prescribed to treat pulmonary arterial hypertension, a condition where blood pressure in the lungs is higher than it should be (Smith, 2021).

Sildenafil is approved by the U.S. Food and Drug Administration (FDA) for ED in doses of 25 mg, 50 mg, and 100 mg. It may also be prescribed off-label for ED at 20 mg, 40 mg, 60 mg, 80 mg, and 100 mg doses. Increasing your dosage in smaller increments can make finding an optimal dose easier for you and your healthcare provider (DailyMed, 2020).

The highest available dose of sildenafil is 100 mg, but that doesn't mean it's the right dose for you. Sildenafil 100 mg tablets can have serious side effects, which are more dangerous at higher doses. 

How long does sildenafil 100 mg last? 

Sildenafil starts working within 30–60 minutes. Some men find that it works even faster. You should take sildenafil between 30 minutes and four hours before sexual activity. The medication usually stays in your system for 4–5 hours (Zucchi, 2019; DailyMed, 2020).

How to take sildenafil 100 mg

Ideally, you should take Viagra about 30–60 minutes before sex for maximum effect. Remember, it won't give you an erection if you are not already sexually aroused. 

You can take Viagra with or without food, but know that eating a high-fat meal can decrease drug absorption and make it take longer to start working. Taking sildenafil on an empty stomach may allow it to work faster (Zucchi, 2019). 

Sildenafil 100 mg cost

The price of sildenafil 100 mg varies depending on your insurance coverage, where you live, and where you purchase the medication. According to a popular prescription-discount site, the retail price for ten tablets of generic sildenafil 100 mg is about $9 compared to more than $670 for the brand name Viagra (GoodRx, 2020).

What is Viagra used for?

Viagra (sildenafil) is an oral medication for ED. It's part of a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors, which also includes tadalafil (brand name Cialis), vardenafil (brand name Levitra), and avanafil (brand name Stendra). 

PDE5 inhibitors like sildenafil work by blocking an enzyme called PDE5, which makes blood vessels smaller. During an erection, a natural chemical called cGMP opens up blood vessels in the penis, increasing blood flow and making the penis harder. Since PDE5 stops cGMP (therefore blocking erections), inhibiting PDE5 allows cGMP to work its magic and make erections last longer (Smith, 2021).

Keep in mind: you don't automatically get an erection taking sildenafil or other PDE5 inhibitors––you need sexual stimulation for them to work.

Cialis Important Safety Information: Read more about serious warnings and safety info.

What is erectile dysfunction?

ED is when you can't get or keep an erection long enough to have satisfying sex. That includes erections that aren't as firm or don't last as long as you'd like. Some people with ED have trouble getting morning erections as well.

Experts believe around 30–50 million American men have experienced ED at some point. It can happen at any age but becomes more common as men get older. By the time a man is in his 40s, he has about a 40% chance of having experienced ED at some point. That likelihood increases by about 10% for each decade of life (Ferrini, 2017; Sooriyamoorthy, 2021).

That said, ED is not considered a "natural" part of aging. It can also be caused by serious health conditions, including (Sooriyamoorthy, 2021):

  • Heart disease: This occurs when plaque builds up in the arteries, reducing blood flow to the heart. The same process can restrict blood flow to the penis, leading to ED. 

  • Diabetes: Diabetes is characterized by high blood sugar, which can damage blood vessels and disrupt proper blood flow. This, in turn, can trigger ED.

  • Hypertension: Also called high blood pressure, this is when blood pumps through blood vessels too forcefully, damaging and narrowing those blood vessels.

  • AnxietyPersonal things like relationship problems and performance anxiety can also cause ED.  

It's smart to consult a healthcare professional at the first sign of ED so they can assess your overall health and nip any serious issues in the bud. There are several other treatments for ED besides oral medications. These include (Sooriyamoorthy, 2021):

  • Medications injected into the penis (such as alprostadil, BiMix, and TriMix)

  • Lifestyle changes like eating a healthy diet, regularly exercising, losing weight, avoiding tobacco, and drinking less alcohol 

  • Surgery to correct conditions that can cause ED, such as Peyronie's disease

  • Devices that can help blood flow into and stay in the penis like cock rings and penis pumps

  • Counseling to improve mental health issues that might contribute to ED

Considerations when taking sildenafil 100 mg

Sildenafil can cause low blood pressure. If this occurs, it’s usually within 1–2 hours after taking it. If you have low blood pressure, a history of heart attack or stroke, or other medical issues ​​(like heart problems or heart failure), talk with your healthcare professional about whether you should take sildenafil (DailyMed, 2020).

You shouldn't take sildenafil if you’ve had an allergic reaction to the medication or any inactive ingredients in it. Don't take sildenafil if you're not healthy enough for sexual activity. If you have any questions about whether you're fit enough for sex, talk with a healthcare provider.

Sildenafil 100 mg side effects

Like many medications, sildenafil and other ED medications can cause side effects. Common side effects of sildenafil include (Smith, 2021): 

  • Headaches

  • Facial flushing

  • Indigestion or heartburn

  • Back pain

  • Stuffy nose

  • Lightheadedness

  • Nausea 

Rarely, sildenafil can cause temporary color vision changes. If you have an eye condition called retinitis pigmentosa, check with your healthcare provider before using PDE5 inhibitors like sildenafil. It may also increase the risk of non-arteritic ischemic optic neuropathy (NAION) in some people––this is an eye problem that can lead to vision loss. 

Sildenafil can also cause priapism, a prolonged erection lasting more than four hours. Seek medical help immediately if you experience priapism, as it can cause irreversible damage if left untreated (Smith, 2021). 

Sildenafil 100 mg drug interactions

Viagra might cause adverse reactions when taken with other medications––both over-the-counter and prescription medicines. So be sure to tell your healthcare provider about any drugs you’re taking before starting sildenafil.

Sildenafil and other PDE5 inhibitors should never be taken with nitrates. These include the prescription medications for chest pain (like nitroglycerin) and the recreational drug amyl nitrite, also known as "poppers." Taking sildenafil with nitrates can cause a dangerous (and potentially fatal) drop in blood pressure (Smith, 2021). 

Certain drugs affect the CYP3A4 enzyme in the liver—this is the system responsible for breaking down sildenafil. Also called CYP34A inhibitors, these drugs allow sildenafil to stick around longer, increasing its concentration in your blood and the risk of side effects. Examples of CYP34A inhibitors include (DailyMed, 2020):

  • Ritonavir

  • Saquinavir

  • Erythromycin

  • Antifungals (like ketoconazole and itraconazole) 

If you take medications to lower high blood pressure (antihypertensives), taking Viagra can cause your blood pressure to drop even further. 

This is especially true if you are taking an alpha-blocker antihypertensive like doxazosin. Alpha-blockers aren’t just for high blood pressure. Tamsulosin (brand name Flomax), an alpha-blocker also used to treat prostate issues (like benign prostatic hyperplasia), can have the same low blood pressure effect if taken with Viagra. 

Avoid combining sildenafil with other PDE5 inhibitors (like Revatio for pulmonary hypertension) or other ED treatments (like Cialis and Levitra) to avoid the potential risk of a drop in blood pressure (DailyMed, 2020). 

Lastly, do not take Viagra if you also take riociguat for pulmonary hypertension because your blood pressure may drop too low. There may be other potential drug interactions with sildenafil 100 mg tablets. Seek medical advice from your pharmacist or healthcare professional if you have questions or concerns (DailyMed, 2021). 

Sildenafil (Generic Viagra)

Same active ingredient as the “Little Blue Pill” for up to 95% less

Where to buy sildenafil 100 mg

Viagra is not available over-the-counter. You need to obtain a prescription for it. That's because sildenafil can cause serious side effects, and it shouldn't be taken by people with certain medical conditions or taking medications.

When buying sildenafil online, beware of counterfeit drugs. Many online ads promising Viagra for cents on the dollar are not legit, and the product they sell can be dangerous. They can contain too little or too much sildenafil, contaminants, and other substances. 

One study found that up to 77% of sildenafil sold online may be counterfeit. When you buy from these sketchy sites, you never really know what you're getting. If you're interested in taking sildenafil 100 mg to resolve ED, the best course of action is to consult a healthcare provider and get a prescription from a reputable source (Yafi, 2018). 


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

December 13, 2021

Written by

Michael Martin

Fact checked by

Chimene Richa, MD

About the medical reviewer

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.

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