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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.
Sildenafil, also known as Viagra (see Important Safety Information), is an effective treatment for erectile dysfunction, but it doesn’t take effect instantly and you need to be in the mood for it to work.
So if you take it expecting fireworks, it’s understandable if you’re disappointed by the fact that it may take some time to get things going. That doesn’t mean you should try a double dose, though. If you don’t think your prescription is working as it should, it’s important to talk to a healthcare professional about your dose instead of taking more than what you were prescribed.
When prescribing medication, healthcare providers try to use the minimum effective dose: the smallest dose that will work for you. That’s because as you use more medication, the risk of side effects increases. Sildenafil is no exception.
Those side effects you may experience include headache, redness in your face, changes in vision, stuffy nose, muscle aches, back pain, nausea, dizziness, and rash (Dhaliwal, 2020).
Even within the range of doses commonly prescribed, how often these side effects occur can increase dramatically as you increase the dose. For example, headaches happen in 16% of people who take 25 mg sildenafil, but 28% of people who take 100 mg.
Sildenafil may also cause priapism, a persistent and painful erection. This serious side effect is considered a medical emergency and requires immediate attention from a healthcare professional (Dhaliwal, 2020).
There have been numerous reports of people who have taken more than the recommended amount of Viagra. We don’t know all the risks, but people who take too much consistently experience an eye problem called retinal toxicity. This can include seeing flashes of light and experiencing red-tinted and blurred vision caused by damage to the cells in his eyes responsible for color vision (Yanoga, 2018).
Vision changes are a common side effect of sildenafil, and they generally resolve within 24 hours at regular doses, but researchers suggest that some people may be more sensitive to sildenafil than others. Vision changes lasting 21 days happened in men taking a standard 100 mg dose of the drug (Karaarslan, 2020).
It’s impossible to know ahead of time whether you might experience these vision changes when taking sildenafil. Ensuring that you can tolerate the medication is one reason healthcare providers will typically start you on a smaller dose and increase the dose according to your needs. Following their instructions minimizes your risk of adverse effects.
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How do I know how much sildenafil I should take?
You should take the recommended dose of sildenafil your healthcare provider has prescribed and no more. You also shouldn’t take sildenafil more than once every 24 hours. Your healthcare provider will likely start you on a 50 mg dose of the medication to test how well you respond. Your healthcare provider may increase your dose to 100 mg or decrease it to 25 mg depending on whether you experience side effects.
You should take sildenafil at least 30 minutes before sex, but it can be taken up to four hours in advance. If you feel that your prescription isn’t effective discuss your options with your healthcare provider. Do not take an extra dose of sildenafil if the first one didn’t work.
If you took sildenafil 30 minutes before sex or less, its effect may strengthen if you wait. But if it still isn’t working well enough to have sex, your healthcare provider may decide a different dose, or another medication entirely, is right for you.
There are also some additional treatments you can try when taking sildenafil to get better results. One option is the vacuum erection device which significantly improved erections in men with diabetes who previously didn’t respond to medication alone (Sun, 2014).
Low-dose vs. high-dose sildenafil
A dose of 25 mg sildenafil is considered a low dose, and low-dose sildenafil is generally only used in certain circumstances. If you’re over the age of 65 or if you’ve ever experienced side effects when taking the standard starting dose (50 mg), you may be prescribed low-dose sildenafil (FDA, 2014).
If you have kidney or liver medical conditions or are taking certain medications, your healthcare provider may prescribe low-dose sildenafil. Sildenafil is broken down in your liver by a system called CYP3A4. Some medications affect this system and, as a result, the rate at which your body can break down drugs like sildenafil. This could cause levels of sildenafil to build up in your system, potentially increasing your risk of side effects, even at low doses (FDA, 2014).
Researchers have used doses as high as 200 mg to successfully treat severe erectile dysfunction, but it’s not a silver bullet, and more research is needed . One small study looked at people who had previously not responded to this medication. High-dose sildenafil improved erectile dysfunction in just 13 of the 54 participants (24.1%). At the highest dose, 63% of the study participants reported experiencing side effects like headaches and facial flushing, which was true even in patients who didn’t get relief from their ED (McMahon, 2002).
And even among people for whom the medication worked, the side effects were so severe that some people decided it wasn’t worth it. Of the 13 people who did see success with the high-dose treatment, four (31%) refused to continue because of the adverse effects. Your healthcare provider will weigh the pros and cons of treatment with these high doses to help you make the decision that’s right for you.
How often can you take sildenafil?
You should always follow the dosing instructions that come with your medication. Whether your healthcare provider prescribed you 25 mg, 50 mg, or 100 mg of sildenafil, you shouldn’t take this drug more than once per 24-hour period. If you’ve taken sildenafil and you feel like it’s not working, do not take another dose.
Taking sildenafil more often than this can cause the medication to build up in your system. This increases your risk of side effects, some of which can be serious. Instead of taking more, speak with your healthcare provider so you can figure out if you need a dose adjustment or an alternative treatment.
Testing for erectile dysfunction
If sildenafil doesn’t work for you, there are plenty of other options. Your healthcare provider may try working with you first to see if there are ways to get you to respond to sildenafil. Taking the medication with a heavy, high-fat meal, for example, may slow your absorption of the drug and cause it to take longer to kick in (FDA, 2014). Modifying what you eat before you take the medication could fix the problem in these circumstances.
If sildenafil doesn’t work for you, your healthcare provider may try an alternative from the same class of medications. Sildenafil is part of a class of drugs known as PDE5 inhibitors, which includes a range of alternative options. Tadalafil (Cialis; see Important Safety Information), vardenafil (Levitra), avanafil (Strendra) are also PDE5 inhibitors and may be worth a try.
These medications all work similarly, but their differences may be significant for your sex life.
- Tadalafil takes 1-2 hours to work, unlike sildenafil’s 30 minutes, but its effects can last up to 36 hours off and on. This medication is available in a daily tablet (Daily Cialis) tadalafil) while other members of this drug class are taken in anticipation of having sex.
- If you’re probably going to take your medication with food, vardenafil may be the best option for you. High-fat meals can slow down how quickly certain PDE5 inhibitors work. But vardenafil works at the same speed even when taken with a moderate-fat meal (Bourin, 2018).
- Avanafil kicks in for many people within 15 minutes, making it the fastest-acting PDE5 inhibitor currently available and the best option for some people (NIH, 2019).
If pills aren’t for you…
It’s hard to compete with the ease of taking a pill, but non-pill options may work better for you. Alprostadil, one ED medication, is available as an injection, topical cream, and intraurethral suppository (a medication that you put into your penis using an applicator)(Jain, 2020). It may take getting used to injections, but this type of therapy has a high success rate when it comes to giving you an erection hard enough for sex (Coombs, 2012).
It’s dangerous to take higher doses of sildenafil than your healthcare provider prescribes, and doing so can cause lasting damage to your vision. If the amount you’re prescribed isn’t working well enough to have sex, there are other options. Your healthcare provider may alter your dose, switch you to a different oral medication, or try an alternative to pills. There are several options with high success rates.
- Bourin, M. (2018). Clinical Pharmacology of Phosphodiesterase 5 Inhibitors in Erectile Dysfunction. SOA Archives of Pharmacy Pharmacology, 1(1). Retrieved from https://scientonline.org/open-access/clinical-pharmacology-of-phosphodiesterase-5-inhibitors-in-erectile-dysfunction.pdf
- Coombs PG, Heck M, Guhring P, Narus J, Mulhall JP. (2012). A review of outcomes of an intracavernosal injection therapy programme. BJU International 110(11), 1787-1791. doi:10.1111/j.1464-410X.2012.11080.x. Retrieved from https://pubmed.ncbi.nlm.nih.gov/22564343/
- Dhaliwal, A., Gupta, M. (2020, June 23). PDE5 Inhibitor. StatPearls Publishing. Treasure Island, FL. https://www.ncbi.nlm.nih.gov/books/NBK549843/
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- Huang, Y., Xu, C., Zhu, Q., Zhang, Y., & Lin, B. (2019). High dose sildenafil citrate induced persistent binocular anomalopia: A case report. Research Square. doi:10.21203/rs.2.308/v1. Retrieved from https://europepmc.org/article/ppr/ppr148379
- Karaarslan, C. (2020). Ocular Side Effects of Sildenafil That Persist Beyond 24 h—A Case Series. Frontiers in Neurology, 11(67). doi:10.3389/fneur.2020.00067. Retrieved from https://www.frontiersin.org/articles/10.3389/fneur.2020.00067/full
- Kim, H. D., Chang, J. H., Kim, Y. K., & Ohn, Y. (2017). Electrophysiologic effects of Very high-dose Sildenafil. JAMA Ophthalmology, 135(2), 165. doi:10.1001/jamaophthalmol.2016.4017. Retrieved from https://jamanetwork.com/journals/jamaophthalmology/article-abstract/2595044
- Kolomeyer, A. M., & Kim, B. J. (2018). High-Dose sildenafil-associated Acute Macular Neuroretinopathy Variant. Ophthalmology Retina, 2(7), 711. doi:10.1016/j.oret.2017.08.024. Retrieved from https://www.ophthalmologyretina.org/article/S2468-6530(17)30382-2/pdf
- McMahon, C.G. (2002). High dose sildenafil citrate as a salvage therapy for severe erectile dysfunction. International Journal of Impotence Research, 14(6), 533-538. doi:10.1038/sj.ijir.3900936. Retrieved from https://pubmed.ncbi.nlm.nih.gov/12494291/
- National Health Institutes (NIH). (2019, September 30). DailyMed – STENDRA- avanafil tablet. Retrieved from https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a8726f90-9329-46ca-9379-2b50c78fe0e2
- National Health Institutes (NIH). (2020, February 3). DailyMed – VIAGRA- sildenafil citrate tablet, film coated. Retrieved from https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=a2a9f459-e692-4e85-83b0-a35fbf35e91b
- Rajagopalan, P., Mazzu, A., Xia, C., Dawkins, R., Sundaresan, P. (2003). Effect of high-fat breakfast and moderate-fat evening meal on the pharmacokinetics of vardenafil, an oral phosphodiesterase-5 inhibitor for the treatment of erectile dysfunction. Journal of Clinical Pharmacology, 43(3):260-267. doi:10.1177/0091270002250604. Retrieved from https://pubmed.ncbi.nlm.nih.gov/12638394/
- Seidman, S.N., Pesce, V.C., Roose, S.P. (2003). High-dose sildenafil citrate for selective serotonin reuptake inhibitor-associated ejaculatory delay: open clinical trial. Journal of Clinical Psychiatry, 64(6), 721-725. doi:10.4088/jcp.v64n0616. Retrieved from https://pubmed.ncbi.nlm.nih.gov/12823089/
- Sun, L., Peng, F., Yu, Z., Liu, C., Chen, J. (2014). Combined sildenafil with vacuum erection device therapy in the management of diabetic men with erectile dysfunction after failure of first-line sildenafil monotherapy. International Journal of Urology, 21(12), 1263-1267. doi:10.1111/iju.12564. Retrieved from https://onlinelibrary.wiley.com/doi/abs/10.1111/iju.12564
- Yanoga F., Gentile, R.C., Chui, T.Y.P, Freund, K.B., Fell, M., Dolz-Marco, R., Rosen, R.B. (2018). Sildenafil Citrate Induced Retinal Toxicity – ERG, OCT, and Adaptive Optics findings. Retinal Cases and Brief Reports, 12(Suppl 1), S33-S40. doi:10.1097/ICB.0000000000000708. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6110976/