What Dose of Sildenafil Should I Take?

Written by
The Manual Team
Medically approved by
Dr Earim Chaudry
Last updated
2nd June 2021

In 30 seconds

Sildenafil – or the branded drug Viagra, which uses Sildenafil as its active ingredient – is one of the most popular treatments for erectile dysfunction (ED) on the market. Yet, as with all medicines, it’s crucial that you get all the information you need before you take it.

One of the important questions you should be asking concerns Sildenafil doses. The drug is available in 25mg, 50mg and 100mg options – with 50mg being the standard option. If this dose of Sildenafil doesn’t help you achieve an erection firm enough for sex, the 100mg dosage might be preferable.

Taking too much Sildenafil does increase the risk of side effects – so do not exceed 100mg a day. If you react badly to the 50mg tablet, the lower-strength 25mg might improve your sexual performance while avoiding the side effects. 

Treating Erectile Dysfunction

Erectile dysfunction (ED) is a hugely common condition, with up to 20% of men in the UK experiencing difficulties achieving or sustaining erections. It is not just older men who suffer from it either, as the common myth goes. Rather, as many as half of men under forty years of age struggle with the condition too. 

There’s no doubt that ED can be a very frustrating condition. It knocks your confidence in the bedroom and can make you shy away from sexual activity altogether, which is not something that you or your partner will want.

You may find that your ED is only temporary – perhaps caused by stress or personal issues. But if it seems to be sticking around, know that effective treatment of erectile dysfunction is possible. 

Most likely you’ve already heard of Viagra or Revatio, with its active agent, Sildenafil Citrate. However, it’s important to know what you are letting yourself in for before you try it. In this article, we’re going to consider one of the most important questions about Sildenafil medication: the dosages. 

So, how much Sildenafil is safe to use? And what’s normal?

Read on to find out.

What Does Sildenafil Do?

Sildenafil is part of a group of drugs known as PDE5 inhibitors. These drugs – including Tadalafil (Cialis) and Vardenafil (Levitra) too – control the activity of an enzyme with the catchy name phosphodiesterase type-5

When PDE5 is at work, it regulates blood flow into the penis by influencing the smooth muscle contraction of the blood vessels supplying the penis. This means it is a useful target to potentiate blood flow in men who have erectile dysfunction. And that’s where Sildenafil, and other PDE5 inhibitors, come in.

Originally, Viagra was designed by Pfizer as a drug to help high blood pressure, or pulmonary arterial hypertension — but it actually did something else. That was to temporarily stop the action of the PDE5 enzyme, thus enabling increased blood flow to the penis when you are sexually aroused. This should enable you to achieve and maintain a firm enough erection to have sex.

Important note: Sildenafil is only approved as an ED treatment for men over the age of 18.

What Dose of Sildenafil Should I Take?

There are three different Sildenafil dosages available: 25mg, 50mg, and 100mg tablets. Regardless of strength, only one tablet should be taken per day – as it takes 24 hours for the drug to fully leave your body.

It’s recommended that you take a Sildenafil tablet around one hour before you plan to have sex. However, it can kick in after 30 minutes, and will last for 4 hours after you have taken it. Importantly, though, Sildenafil effects will be felt with sexual stimulation. So, after you’ve swallowed the tablet just relax and enjoy some intimate time with your partner. And remember, there may be a delayed onset after a high-fat meal.

Let’s look at the three different doses of Sildenafil and how they compare:

The 50mg Sildenafil Dose

50mg is the starting dose of Sildenafil for ED and the one you’re most likely to be prescribed. Research has shown that a 50 mg dose is enough for 74% of men to experience improved erections. Note that if you want to buy Sildenafil over the counter then you are restricted to a 50mg dose (available as Viagra Connect).

If you try the 50mg dose and it doesn’t work for you the first time, it’s recommended that you give it a go on a few more occasions before switching to the higher dose. In fact, evidence suggests trying a dose on up to 8 separate occasions before increasing your dose. You may need to relax a little, or cut down on alcohol too.

If it doesn’t work for you at all, an alternative such as Tadalafil might be a more successful alternative. 

The Low Dose: 25mg

As the lowest recommended dose of Sildenafil, you may be prescribed the 25mg tablet if you’re experiencing any uncomfortable side effects from the 50mg. This reduced strength dose still helps 62% of men get a firmer erection, while side effects may be fewer or less likely to occur.

If you’re over 65 years old and already receiving treatment for liver, kidney, or heart problems, or other age-related conditions, then you could be prescribed the lower Sildenafil dose to avoid problematic interaction with existing medications.

The Highest Sildenafil Dose: 100mg

This is the maximum recommended dose of Sildenafil, which you might be prescribed if the 50mg is not enough to effectively treat your ED. The 100mg tablet doesn’t have a longer-lasting impact than the lower doses, but the effect may be stronger – it has been shown that 82% of men have improved erections with this dosage.

Be careful, though. A higher dosage does not necessarily mean a better, or more successful experience. While you are improving your chances of achieving an erection with the higher dose, the risk of side effects is higher too. 

Side Effects and Drug Interactions

Something that often gets forgotten with the more famous medicines is that they are indeed medicines. The same applies to Sildenafil or Viagra. You shouldn’t take these drugs unless you need to, and you should be aware of the risk of side effects too. 

Possible side effects of Sildenafil include nausea, dizziness, headache, a blocked nose, and facial flushing. While these are the most common side effects, they remain rare: Sildenafil is generally well-tolerated. If you are someone with low blood pressure, though, be cautious. The US Food and Drugs Agency (FDA) notes that Sildenafil can lower your blood pressure too.

More serious side effects, meanwhile, are rare. These include loss of vision or a painful and prolonged erection known as priapism. Seek the immediate attention of a healthcare professional if these do occur.

Importantly, you should be particularly careful when taking Sildenafil if you are on other medications. These include treatment for medical conditions such as chest pain or heart disease, or drugs known as alpha-blockers, such as doxazosin. Sildenafil is known to interact with prescription drugs like erythromycin, itraconazole, and ketoconazole too, as well as treatment for pulmonary hypertension, such as Riociguat.

If you are taking any of these drugs, talk to your clinician for medical advice first – as it will affect the dose that you can safely take.

Key Takeaways…

When you take Sildenafil as a treatment for ED, more often than not, the 50mg tablet will be enough. This should help you to achieve a firmer, longer-lasting erection for more satisfying sex. 

However, if you feel that you need a different dose you can always consult with the clinicians at Manual. They may recommend the lower 25mg tablet for fewer side effects or up the dose to increase the chance of a successful erection. 

Remember: It’s important that you only take the dose prescribed for you, to keep yourself safe and to experience the most effective treatment for your ED. Treatment for erectile dysfunction is individualised, meaning that what works for one person may not work for another. Everybody is different – so bear this in mind when researching ED medication.


  1. Atomik Research -Co-Op Pharmacy Erectile Dysfunction PR Survey: https://www.atomikresearch.co.uk/case-studies-archive/co-op-pharmacy-erectile-dysfunction-pr-survey/

  2. emc -Sildenafil 100 mg film-coated tablets: https://www.medicines.org.uk/emc/product/7124/smpc

  3. VIAGRA (sildenafil citrate) Tablets Description: https://www.accessdata.fda.gov/drugsatfda_docs/label/2010/020895s033lbl.pdf

While we've ensured that everything you read on the Health Centre is medically reviewed and approved, information presented here is not intended to be a substitute for professional medical advice, diagnosis, or treatment. It should never be relied upon for specific medical advice. If you have any questions or concerns, please talk to your doctor.

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