Editing Sildenafil (section)

==Adverse effects==
In [[clinical trial]]s, the most common [[Adverse drug reaction|adverse effects]] of sildenafil use included [[headache]], [[Flushing (physiology)|flushing]], [[indigestion]], [[nasal congestion]], and impaired vision, including [[photophobia]] and [[blurred vision]].<ref name="Viagra FDA label" /> Some sildenafil users have complained of seeing everything tinted blue ([[cyanopsia]]).<ref>{{cite web | url = http://www.visionweb.com/content/consumers/dev_consumerarticles.jsp?RID=85 | title = Viagra and Vision | date = 29 October 2001 | publisher = VisionWeb | access-date = 5 November 2016 |archive-url = https://web.archive.org/web/20170610174402/http://www.visionweb.com/content/consumers/dev_consumerarticles.jsp?RID=85 | archive-date = 10 June 2017}}</ref> This cyanopsia can be explained because sildenafil, while selective for PDE<sub>5</sub>, does have some affinity for PDE<sub>6</sub>, which is the phosphodiesterase found in the retina. Patients thus taking the drug may experience colorvision abnormalities. Some complained of blurriness and loss of [[peripheral vision]]. In July 2005, the US [[Food and Drug Administration]] (FDA) updated labeling for [[tadalafil]] (Cialis), [[vardenafil]] (Levitra), and sildenafil (Viagra) to reflect a small number of post-marketing reports of sudden vision loss, while acknowledging that "...it is not possible to determine whether these oral medicines for erectile dysfunction were the cause of the loss of eyesight or whether the problem is related to other factors such as high blood pressure or diabetes, or to a combination of these problems."<ref>{{cite press release | title = FDA Updates Labeling for Viagra, Cialis and Levitra for Rare Post-Marketing Reports of Eye Problems | url = https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2005/ucm108458.htm | publisher = U.S. [[Food and Drug Administration]] (FDA) | access-date=5 November 2016 | archive-url = https://web.archive.org/web/20161022204628/https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2005/ucm108458.htm | archive-date = 22 October 2016 | date = 8 July 2005}}</ref> A careful review of pooled data from clinical trials containing well documented information about the dose and duration of exposure to the drug for a large number of patients, yields no evidence for an increased risk of [[Anterior ischemic optic neuropathy|non-arteritic anterior ischemic optic neuropathy]] or other adverse ocular events associated with PDE5 inhibitor use.<ref name="Laties">{{cite journal | vauthors = Laties AM | title = Vision disorders and phosphodiesterase type 5 inhibitors: a review of the evidence to date | journal = Drug Safety | volume = 32 | issue = 1 | pages = 1–18 | date = January 2009 | pmid = 19132801 | doi = 10.2165/00002018-200932010-00001 | s2cid = 207296076 }}</ref>

Rare but serious adverse effects found through [[postmarketing surveillance]] include [[Priapism|prolonged erections]], severe [[Hypotension|low blood pressure]], [[myocardial infarction]] (heart attack), [[Ventricular tachycardia|ventricular arrhythmias]], [[stroke]], increased [[intraocular pressure]], and [[sudden sensorineural hearing loss|sudden hearing loss]].<ref name="Viagra FDA label" /> In October 2007, the FDA announced that the labeling for all PDE<sub>5</sub> inhibitors, including sildenafil, required a more prominent warning of the potential risk of sudden hearing loss.<ref>{{cite web | title = FDA Announces Revisions to Labels for Cialis, Levitra and Viagra | url = https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2007/ucm109012.htm | publisher = U.S. [[Food and Drug Administration]] (FDA) | access-date = 5 November 2016 | archive-url = https://web.archive.org/web/20161022203200/https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2007/ucm109012.htm | archive-date = 22 October 2016 | date = 18 October 2007}}</ref>

=== Interactions ===
Care should be exercised by people who are also taking [[Protease inhibitor (pharmacology)|protease inhibitors]] for the treatment of [[HIV/AIDS|HIV infection]]. Protease inhibitors inhibit the metabolism of sildenafil, effectively multiplying the plasma levels of sildenafil, increasing the incidence and severity of side effects. Those using protease inhibitors are recommended to limit their use of sildenafil to no more than one 25&nbsp;mg dose every 48 hours.<ref name="Viagra FDA label" /> Other drugs that interfere with the metabolism of sildenafil include [[erythromycin]] and [[cimetidine]], both of which can also lead to prolonged plasma half-life levels.<ref>{{cite journal | vauthors = Schwartz BG, Kloner RA | title = Drug interactions with phosphodiesterase-5 inhibitors used for the treatment of erectile dysfunction or pulmonary hypertension | journal = Circulation | volume = 122 | issue = 1 | pages = 88–95 | date = July 2010 | pmid = 20606131 | doi = 10.1161/CIRCULATIONAHA.110.944603 | s2cid = 13207143 | doi-access = free }}</ref>

The use of sildenafil and an [[Alpha-1 blocker|α<sub>1</sub> blocker]] (typically prescribed for [[hypertension]] or for urologic conditions, such as [[benign prostatic hypertrophy]]) at the same time may lead to low blood pressure, but this effect does not occur if they are taken at least 4 hours apart.<ref name="Kloner">{{cite journal | vauthors = Kloner RA | title = Pharmacology and drug interaction effects of the phosphodiesterase 5 inhibitors: focus on alpha-blocker interactions | journal = The American Journal of Cardiology | volume = 96 | issue = 12B | pages = 42M–46M | date = December 2005 | pmid = 16387566 | doi = 10.1016/j.amjcard.2005.07.011 }}</ref>

===Contraindications===
[[Contraindications]] include:<ref name="Viagra FDA label">{{cite web | title=Viagra- sildenafil citrate tablet, film coated | website=DailyMed | url=https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0b0be196-0c62-461c-94f4-9a35339b4501 | access-date=6 October 2020 | archive-date=13 August 2020 | archive-url=https://web.archive.org/web/20200813210523/https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0b0be196-0c62-461c-94f4-9a35339b4501 | url-status=live }}</ref>
* Concomitant use of nitric oxide donors, organic nitrites and nitrates,<ref name="ACC/AHA">{{cite journal | vauthors = Cheitlin MD, Hutter AM, Brindis RG, Ganz P, Kaul S, Russell RO, Zusman RM | title = ACC/AHA expert consensus document. Use of sildenafil (Viagra) in patients with cardiovascular disease. American College of Cardiology/American Heart Association | journal = Journal of the American College of Cardiology | volume = 33 | issue = 1 | pages = 273–82 | date = January 1999 | pmid = 9935041 | doi = 10.1016/S0735-1097(98)00656-1 | doi-access = free }}</ref> such as:
** [[Nitroglycerin (drug)|nitroglycerin]]
** [[isosorbide mononitrate]]
** [[isosorbide dinitrate]]
** [[sodium nitroprusside]]
** [[alkyl nitrites]] (commonly known as "[[poppers]]")
* Concomitant use of [[soluble guanylyl cyclase]] stimulators, such as [[riociguat]]
* Known hypersensitivity to sildenafil

Sildenafil should not be used if sexual activity is inadvisable due to underlying cardiovascular risk factors.<ref>{{Cite news|url=https://www.rxlist.com/viagra-drug.htm#warnings_precautions|title=Viagra (Sildenafil Citrate): Side Effects, Interactions, Warning, Dosage & Uses|work=RxList|access-date=11 July 2018|archive-date=12 July 2018|archive-url=https://web.archive.org/web/20180712002957/https://www.rxlist.com/viagra-drug.htm#warnings_precautions|url-status=live}}</ref>