Medically reviewed by Vicky Davis, FNP
Written by Our Editorial Team
Last updated 3/08/2021
Sildenafil is one of the most effective drugs prescribed for the treatment of erectile dysfunction.
If you’re unfamiliar with this medication, then you may recognize it under the brand name Viagra®, where it acts as the active ingredient responsible for its effects.
Sildenafil has been approved for use since 1998 and remains highly recommended for improving erectile function. It is available as an oral medication in 25mg, 50mg and 100mg.
To properly enjoy its benefits, sildenafil is recommended to be taken shortly before sexual intercourse occurs.
We’ll first be examining how this drug helps to improve sexual function, before looking into how long its effects may last. Then, we’ll look into possible side-effects and interactions that may come from using sildenafil.
To help manage erectile dysfunction, sildenafil acts as a PDE-5 inhibitor. This will make a little more sense after we explain the mechanisms that affect erectile function.
Erections typically begin following sexual or physical stimulation, or perhaps erotic inventions. When this happens, the pelvic nerves are stimulated, causing the release of nitric oxide (NO), a neurotransmitter largely responsible for relaxing penile muscles.
This nitric oxide is released across the penile arteries that supply blood to the penis, as well as the cavernosal smooth muscles responsible for providing structure for penile erections.
Working a little harder, NO also causes an increase in cyclic guanosine monophosphate (cGMP) which relaxes smooth muscles and increases blood flow to the penis.
Following the increased blood flow, cGMP encourages the relaxation of smooth muscles which permits the penis to harden into an erection.
However, lying within the cavernous smooth muscles is an enzyme called PDE5. This enzyme breaks down the cGMP, limiting the flow of blood and causing the penile arteries and smooth muscles to contract. This usually leads to a diminished erection.
Putting two and two together, sildenafil works to prevent PDE5 from breaking cGMP down. It does this by binding to the enzyme, allowing for an even more increased concentration of cGMP. This can promote healthy erections.
To answer this question, now would be a good time to point out that 5.3 million prescriptions were written for Viagra within six months of its approval by the FDA. So perhaps yes.
Looking to science, studies have backed the effectiveness of sildenafil as a treatment for erectile dysfunction.
In two sequential double-blind studies, the effectiveness of sildenafil was tested to determine its abilities in treating erectile dysfunction.
For 24 weeks, 532 men were treated with oral sildenafil at 25mg, 50mg or 100mg as well as a placebo.
Another 12-week study was carried out where 329 men were treated to 100mg of sildenafil or a placebo. Following this, 225 of the 329 men entered a 32-week extension study.
It was discovered that higher doses of sildenafil produced improved erectile function.
The men placed on 100mg of sildenafil reported an impressive 100 percent boost in erection success following its use.
Sildenafil is also effective in treating erectile dysfunction brought on by certain chronic illnesses.
In a randomized study, patients with ED who were undergoing hemodialysis for chronic renal failure were observed. Forty-one patients were placed on 50mg of sildenafil and a placebo.
At the end of the study, 85 percent of the patients on sildenafil reported improvements in erectile function, compared to 9.5 percent in the placebo group. While it didn't improve sexual desire, this medication was ruled effective and well-tolerated for the improvement of erectile function in patients with chronic renal failure on hemodialysis.
Sildenafil also works in patients of advanced ages. This is especially important as the likelihood of erectile dysfunction increases between the ages of 40 and seventy-five.
In an analysis of five studies on the effectiveness of sildenafil for erectile dysfunction, data on participants aged 65 and above were pooled together.
These participants also included a group living with diabetes and erectile dysfunction. They were observed over a period of 12 weeks to six months.
At the end of the study, 69 percent of elderly patients living with erectile dysfunction reported that sildenafil improved their ability to achieve erections, compared to 18 percent that received placebos.
Patients with erectile dysfunction and diabetes also reported a 50 percent improvement in erections, compared to 10 percent on placebos.
It’s important to note that while sildenafil is effective in improving erectile function, this effect won’t come to play unless the body is stimulated physically or mentally to produce an erection.
To get the desired effects, sildenafil should first be taken at least an hour before sexual intercourse is expected.
Sildenafil is absorbed quickly and may take around 30 minutes to 120 minutes to reach peak concentration. Its effects may however be delayed for about an hour where a high-fat meal is consumed before dosing.
On how long its effects may last, sildenafil has a half-life of about three to four hours. This simply means that the active amount of viagra in your body reduces by around half after three to four hours.
While sildenafil is an effective medication for treating erectile dysfunction, like most drugs, it isn't without side effects.
Sildenafil doses above 100mg have been reported to produce:
This medication may also cause changes in color vision or otherwise hazy vision. It can also lead to a change in light perceptions.
On rare occasions, it has been found to be toxic to the ear and has resulted in reversible hearing loss.
Because sildenafil can increase blood flow, it should be prescribed with caution to people sensitive to changes in blood pressure, this includes individuals with a history of heart failure, heart attack, stroke in the past six months, high or low blood pressure or chest pain.
Caution is also required when used with the antiretroviral medication ritonavir to avoid an accumulation of sildenafil.
When combining sildenafil with antihypertensive agents, extra care has to be observed. This also extends to any sildenafil mixtures with mixed alpha/beta-blockers.
Also, because sildenafil may lead to prolonged erections lasting longer than four hours, aka priapism, extra care has to be observed where a person lives with an anatomically deformed penis.
Sildenafil is a stamped and approved medication for managing erectile dysfunction.
Its effectiveness runs across different age groups and it may even cause positive effects in individuals living with chronic diseases.
The impact of this drug takes effect around 30 minutes after its consumption. It has an active life which is cut by about half every three to four hours.
To avoid adverse effects, it's important to reach out to a healthcare provider before making use of this medication.