The Independent Pharmacy

What Is Sildenafil? Everything You Need To Know About This Erectile Dysfunction Tablet

Scott McDougall
Scott McDougallMPharmDirector & Registered Manager

Reviewed on 6 Apr 2023

Patented in 1996 and given approval by the FDA in 1998, Sildenafil was the first oral medication to be approved in the US for treating erectile dysfunction — and when it hit the market under Pfizer’s brand name of Viagra, it brought the issue of erectile dysfunction into mainstream awareness, ultimately creating a massive global industry.

In 2012, Pfizer’s patents on the sale of Sildenafil outside the US expired, making it possible for other pharmaceutical companies to produce and distribute it generically or under a name of their choosing. Whether it’s the famous blue pill associated Viagra, or something else entirely, every licensed version of Sildenafil works in the same way.

If you suffer from erectile dysfunction and you’re thinking about using Sildenafil, you should learn about how it functions and what you can expect before you pursue that option. In this article, we’ll cover everything you need to know before proceeding.

Sildenafil Tablets (25mg, 50mg & 100mg)
Sildenafil Tablets (25mg, 50mg & 100mg)
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What is Sildenafil used for?

Sildenafil is a medication, usually found in tablet form, used to treat erectile dysfunction (ED) in men (they are not suitable to be used by women). It is a generic, version of Pfizer’s popular drug Viagra. It works in the same way and has the same active ingredients, but is considerably cheaper.

While Sildenafil is sometimes used to treat conditions involving high blood pressure or restricted blood flow around the body (and was initially formulated to do just that), Sildenafil is far more effective at producing stronger erections — that’s how it was ultimately approved for use, and that’s the purpose for which it’s recommended by medical professionals.

Sildenafil is a prescription-only drug, meaning you can only buy Sildenafil following a consultation. If someone suffering from ED has no other medical conditions or issues that would make it unsuitable, and they’re in adequate health to use it safely, it’s a simple prescription.

Recently, a version of Sildenafil was approved for over-the-counter sale — Viagra Connect — which is now available without a prescription. It can be purchased from the pharmacy without needing to see your doctor, however, you will still need to have a consultation with the pharmacist to ensure it's suitable for you. Bear in mind that it is only available in 50mg strength and the price will be higher (given the relative convenience).

How does Sildenafil work?

Sildenafil tablets taken correctly following a doctors consultation

Achieving and maintaining a strong erection is all about blood flow — the penis stiffens during arousal because its soft and flexible tissue becomes flush with blood, so if there isn’t enough blood circulating, the erection will soon be lost.

In ideal circumstances, the blood vessels around the body are relaxed, allowing them to stay as wide as possible and thus carry blood at a greater rate. This doesn’t always happen, though. An enzyme referred to as PDE5 can break down a vital substance responsible for dilating blood vessels, leading to blood flow being restricted and the flesh of the penis not getting enough.

Sildenafil, like other erectile dysfunction treatments, is a PDE5 inhibitor. After you take the tablet, it circulates around your system and stops PDE5 from getting in the way of blood flow. The result is a temporary but major boost in the ability for blood to flow to the penis, allowing the user to achieve and retain a strong erection much more easily.

How Sildenafil should be used

Firstly, it must be noted that Sildenafil will not produce an erection by itself. It doesn’t drive sexual thoughts or feelings in any way — it simply makes it far easier for sexual arousal to physically manifest as it should.

As such, it should be used to support and enhance regular sexual activity. It’s an ideal single-use treatment: take Sildenafil on an empty stomach (if possible) around an hour before you’ll need it (that should be plenty of time for it to take effect), and you can expect its effects to last between 4-6 hours (check out our page about how long Sildenafil lasts).

You shouldn’t use Sildenafil more than once per day. Bear in mind that a dosage above 100mg won’t improve results and will significantly increase side effects thus, it isn’t worth risking. It also bears noting that you should avoid drinking grapefruit juice before or after you take Sildenafil — it’s thought to affect how your system digests Sildenafil, thus reducing how effective it ends up being.

Is it generally safe?

Sildenafil does have a wide range of possible side effects (you can read about them on our page dedicated to Sildenafil side effects), but the only common ones — affecting around 1 in 10 users — aren’t cause for concern. Realistically, you only need to worry about developing a headache, feeling nauseated, or suffering blurred vision — all temporary.

Overall, Sildenafil is extremely safe when used by someone healthy and determined by a medical professional to be a viable user. Provided you follow the prescribed instructions, you should be able to use it on a regular basis with no major adverse effects, as evidenced by the huge number of people who’ve used it over the past decades (check out our Sildenafil reviews page for comments from our customers).

When you shouldn’t use Sildenafil

Stop sign: when shouldnt Sildenafil tablets be used

There are various circumstances in which Sildenafil should not be used, including (but not limited to) the following:

  • You don’t suffer from erectile dysfunction.
  • You’re younger than 18.
  • You’re allergic to any of the ingredients.
  • You have a serious heart or liver condition.
  • You’re suffering from low blood pressure.
  • You’ve recently had a heart attack or a stroke.
  • You’re taking other medication that affects blood pressure (nitrates, nitric oxide donors, riociguat, and other erectile dysfunction treatments).
  • You have a serious inherited eye disease (check with an expert).

Meanwhile, if any of the following things apply to you, you may be unable to use Sildenafil safely (be honest about your situation to the medical consultant — they’ll let you know):

  • Your heart is weak and/or damaged.
  • You have a significant penile deformity.
  • You have a blood or bone marrow condition (e.g. leukaemia).
  • You have a stomach ulcer.

What to try if it doesn’t work for you

There are three possible scenarios in which you’ll need an alternative to Sildenafil:

  • You’re ineligible to use it for whatever reason (see the list above).
  • It boosts blood flow, but an unrelated issue prevents you from achieving an erection (you can’t get sufficiently aroused due to anxiety, perhaps).
  • It achieves a strong erection, but the side effects make sex undesirable or even unsafe (a headache gets in the way, or your heart can’t take the strain).

You could look at other oral erectile dysfunction medications, such as Tadalafil. It functions in much the same way as Sildenafil but is effective for a much longer time - up to 36 hours. Overall, all oral medications for erectile dysfunction work similarly, however, if you’ve not had the results you wanted with one treatment after eight attempts, you can try a higher strength or another treatment instead.

If you can’t use any medication of this type, it may be a broader health issue that’s holding you back. You may need to treat some underlying condition, lose weight, or change your diet. Alcohol, in particular, combines very poorly with Sildenafil — it can slow down the rate of digestion, decrease nerve sensitivity (making it harder to achieve sexual stimulation), and lower blood pressure even further (a dangerous prospect).


Let’s quickly sum up everything we’ve looked at in this piece:

  • Sildenafil is the generic form of Viagra, taken orally to treat erectile dysfunction.
  • It works by improving blood flow to help achieve an erection.
  • It doesn’t spontaneously produce erections — it just helps you get them when stimulated.
  • It can be used once per day and lasts between 4-6 hours.
  • It still lets your erection go down after sex.
  • It’s extremely safe but can have some minor side effects.
  • It isn’t suitable for everyone (health issues and other medications can interfere).
  • Alternatives are similar — if it doesn’t work for you, you can try a different treatment.

If you’re ready to fill in an online consultation and seek a prescription for Sildenafil, head to our main Sildenafil product page and go from there.


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