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Feb 04, 2022
6 min read

Viagra (sildenafil): uses, side effects, interactions, and more

Viagra, also known as the little blue pill, is a phosphodiesterase-5 inhibitor (PDE5 inhibitor) that healthcare providers prescribe to treat erectile dysfunction. It works by dilating your blood vessels and allowing more blood to flow to the penis. It usually causes only mild side effects like flushing, dizziness, and headaches but can be dangerous if combined with other medications like nitrates.

Disclaimer

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.

Viagra, often referred to as the “little blue pill,” is a brand-name prescription drug best known for treating erectile dysfunction or “ED”. 

ED occurs when you can’t get or maintain an erection for satisfying sex—and it’s very common, affecting 30 million men in the U.S. (Nunes, 2012). If you find that you’re one of those men and are having a difficult time getting or staying aroused, your healthcare provider may recommend Viagra to help you have harder and longer-lasting erections.  

Let’s learn a little bit more about this popular blue pill.

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What is Viagra? 

Viagra (generic name sildenafil citrate; see Important Safety Information) is a prescription drug that helps treat erectile dysfunction (ED). It is one formulation of the drug sildenafil. (Sildenafil is also found in different formulations under the brand name Revatio [see Important Safety Information].)   

Viagra belongs to a class of drugs called PDE5 inhibitors (phosphodiesterase-5 enzyme inhibitors). PDE5 inhibitors work by blocking an enzyme called PDE5, allowing for more blood to flow to your penis so that you can maintain your erection.  

It is important to note that Viagra can only help you get hard and stay hard if you are already aroused. You have to be sexually stimulated for Viagra to work. 

Viagra uses

Viagra is approved by the U.S. Food and Drug Administration (FDA) for the treatment of erectile dysfunction (ED). It has been shown to help up to 65% of men with ED maintain their erections (McMahon, 2019).

The FDA also approves other formulations of sildenafil—the active ingredient in Viagra— for treating a condition known as pulmonary arterial hypertension, or high blood pressure, in your heart and lung arteries. 

Under some circumstances, a healthcare provider might prescribe sildenafil off-label to treat other conditions, including: 

  • Raynaud’s phenomenon: A condition in which there’s poor blood flow in areas like the fingers and toes. In clinical trials, sildenafil was more effective in treating this condition than placebo, although the trials were very small (Corbin, 2004).
  • Altitude sickness: Sildenafil may improve oxygen levels in people with altitude sickness (Perimenis, 2005).
  • Female sexual interest/arousal disorder (FSAID): Biological females with FSAID have trouble getting aroused or experience low desire. In clinical trials, people with FSAID who took sildenafil had a higher number of satisfying sexual events compared to placebo (Tuiten, 2018). 

Risks and side effects of Viagra

Viagra usually causes mild side effects or none at all. Some of the most common side effects of Viagra are (FDA, 2014-a): 

  • Headaches
  • Flushing
  • Dizziness
  • Upset stomach
  • Nasal congestion
  • Body aches

Serious side effects of Viagra happen less often and include: 

  • Low blood pressure (hypotension) and fainting: Since Viagra makes your blood vessels relax, it can make your blood pressure drop, especially if you’re taking a type of medication called an alpha-blocker. This can cause you to collapse or faint. It can also trigger heart problems in people with a history of cardiovascular disease (FDA, 2014-a). 
  • Hearing loss: Viagra can cause sudden hearing loss, usually in one ear. If it occurs, it usually happens within one to three days of starting the drug (McGwinn, 2010; Smith, 2013).
  • Loss of vision: Viagra may cause a condition called non-arteritic anterior ischemic optic neuropathy (NAION), which can cause blurred vision and lead to vision loss. If it occurs, it usually happens in one eye within a few hours of taking the drug (Pomeranz, 2002).
  • Priapism: Priapism is a painful, prolonged erection that you can’t get rid of, even if you’re not aroused. Viagra can cause priapism that lasts four hours or more, although a review of FDA data suggests this side effect is rare (Rezaee, 2020). 
  • Bleeding: Viagra may cause bleeding since it can affect blood cells called platelets, which make your blood clot (FDA, 2014-a). 

Viagra dosages

Viagra and generic Viagra are available by prescription only—they are not sold over the counter. 

Oral tablets come in doses of 25mg, 50mg, and 100mg. Sildenafil also comes in an oral suspension and an injection form. 

The starting dose of Viagra is usually 50mg orally, taken between 30 minutes and four hours before sex. A healthcare provider may increase the dosage based on symptoms, side effects, and any other medications you are taking. 

You can take Viagra pills with food, but it may take longer to work if you take them with a high-fat meal.  

Viagra warnings and drug interactions

Viagra can cause adverse reactions if you combine it with other prescription drugs. Some examples of medications to avoid when you’re taking Viagra include (FDA, 2014-a):

  • Heart medications: Viagra may be dangerous if you take it with certain cardiovascular medicines. These include nitrates (nitroglycerin) and blood pressure medications (especially alpha-blockers such as doxazosin). The combination can cause a dangerous and possibly fatal drop in your blood pressure. 
  • HIV medications: Antiviral medications like ritonavir, which is often taken for HIV, may interfere with your liver’s ability to clear Viagra from your body, causing an increased risk of toxic effects. 
  • Antibiotics and antifungals: Medications that treat bacterial and fungal infections, like erythromycin, itraconazole, and ketoconazole, may also interfere with your liver’s ability to get rid of Viagra. 

Who should avoid Viagra? 

Viagra is more likely to cause adverse effects in people with certain underlying health conditions or risk factors. If you are in any of these groups, you should consult a healthcare provider before you use Viagra (FDA, 2014-a): 

  • People with a known allergy to Viagra, Revatio, or sildenafil
  • People with a higher risk of priapism (such as people with sickle cell anemia, leukemia, or Peyronie’s disease)
  • Anyone taking nitrates or nitrites
  • Anyone taking alpha-blockers or other blood pressure medications
  • Individuals with heart conditions that are considered too risky for sexual activity (for example, heart valve disease like aortic stenosis)
  • People with a history of low blood pressure, irregular heartbeat, or heart failure
  • Anyone who has experienced a stroke or heart attack in the past six months
  • People with a type of chest pain called unstable angina
  • People who are pregnant
  • People with liver or kidney problems

Getting an erection isn’t always easy—there are a number of steps that can go wrong and cause erectile dysfunction. Viagra is a helpful treatment for ED and typically causes only mild to moderate side effects. However, it may be dangerous when combined with certain medications or underlying conditions. Your healthcare provider can help you decide if Viagra is best for your needs. 

References

  1. Corbin, J. D. (2004). Mechanisms of action of PDE5 inhibition in erectile dysfunction. International Journal of Impotence Research, 16, Supplement 1, S4–S7. doi: 10.1038/sj.ijir.3901205. Retrieved from https://www.nature.com/articles/3901205 
  2. Huang, S. & Lie, J. (2013). Phosphodiesterase-5 (PDE5) Inhibitors In the Management of Erectile Dysfunction. Pharmacy and Therapeutics, a Peer-Reviewed Journal for Formulary Management, 38(7), 407, 414-41. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3776492/
  3. Maia, N., Lopes, K. C., & Ganança, F. F. (2021). Otorhinolaryngological adverse effects of urological drugs. International Brazilian Journal of Urology: Official Journal of the Brazilian Society of Urology, 47(4), 747–752. doi: 10.1590/S1677-5538.IBJU.2021.99.06. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8321485/ 
  4. McGwin, G. (2010). Phosphodiesterase Type 5 Inhibitor Use and Hearing Impairment. Archives of Otolaryngology-Head & Neck Surgery, 136(5), 488–492. doi: 10.1001/archoto.2010.51. Retrieved from https://jamanetwork.com/journals/jamaotolaryngology/fullarticle/496308 
  5. Nunes, K. P., Labazi, H., & Webb, R. C. (2012). New insights into hypertension-associated erectile dysfunction. Current Opinion in Nephrology and Hypertension, 21(2), 163–170. doi: 10.1097/MNH.0b013e32835021bd. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4004343/ 
  6. Perimenis, P. (2005). Sildenafil for the treatment of altitude-induced hypoxaemia. Expert Opinion on Pharmacotherapy, 6(5), 835–837. doi: 10.1517/14656566.6.5.835. Retrieved from https://pubmed.ncbi.nlm.nih.gov/15934909/ 
  7. Pomeranz, H. D., Smith, K. H., Hart, W. M., Jr, & Egan, R. A. (2002). Sildenafil-associated nonarteritic anterior ischemic optic neuropathy. Ophthalmology, 109(3), 584–587. doi: 10.1016/s0161-6420(01)00976-9. Retrieved from https://pubmed.ncbi.nlm.nih.gov/11874765/ 
  8. Rezaee, M. E. & Gross, M. S. (2020). Are We Overstating the Risk of Priapism With Oral Phosphodiesterase Type 5 Inhibitors?. The Journal of Sexual Medicine, 17(8), 1579–1582. doi: 10.1016/j.jsxm.2020.05.019. Retrieved from https://pubmed.ncbi.nlm.nih.gov/32622767/ 
  9. Roustit, M., Giai, J., Gaget, O., Khouri, C., Mouhib, M., Lotito, A., et al. (2018). On-Demand Sildenafil as a Treatment for Raynaud Phenomenon: A Series of n-of-1 Trials. Annals of Internal Medicine, 169(10), 694–703.  doi:10.7326/M18-0517. Retrieved from https://www.acpjournals.org/doi/10.7326/M18-0517 
  10. Smith, B. P. & Babos, M. (2021). Sildenafil. [Updated Jun 29, 2021]. In: StatPearls [Internet]. Retrieved on Jan. 31, 2022 from: https://www.ncbi.nlm.nih.gov/books/NBK558978/
  11. Smith, W. B., 2nd, McCaslin, I. R., Gokce, A., Mandava, S. H., Trost, L., & Hellstrom, W. J. (2013). PDE5 inhibitors: considerations for preference and long-term adherence. International Journal of Clinical Practice, 67(8), 768–780. doi: 10.1111/ijcp.12074. Retrieved from https://pubmed.ncbi.nlm.nih.gov/23869678/ 
  12. Sooriyamoorthy, T. & Leslie, S. W. (2020). Erectile dysfunction. [Updated Aug 12, 2021]. In: StatPearls [Internet]. Retrieved on Jan. 31, 2022 from https://www.ncbi.nlm.nih.gov/books/NBK562253/ 
  13. Tuiten, A., van Rooij, K., Bloemers, J., Eisenegger, C., van Honk, J., Kessels, R., et al. (2018). Efficacy and Safety of On-Demand Use of 2 Treatments Designed for Different Etiologies of Female Sexual Interest/Arousal Disorder: 3 Randomized Clinical Trials. The Journal of Sexual Medicine, 15(2), 201–216. doi: 10.1016/j.jsxm.2017.11.226. Retrieved from https://pubmed.ncbi.nlm.nih.gov/29289554/ 
  14. United States Food and Drug Administration (FDA). (2014-a). Highlights of Prescribing Information: Viagra. Retrieved on Jan. 31, 2022 from https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/20895s039s042lbl.pdf 
  15. United States Food and Drug Administration (FDA). (2014-b). Highlights of Prescribing Information: Revatio. Retrieved on Jan. 31, 2022 from https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/021845s011,022473s004,0203109s002lbl.pdf 
  16. Yafi, F. A., Jenkins, L., Albersen, M., Corona, G., Isidori, A. M., Goldfarb, S., et al. (2016). Erectile Dysfunction. Nature Reviews Disease Primers, 16003(2). doi: 10.1038/nrdp.2016.3. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK558978/