Sildenafil Dosage: Choosing the Right Dose for You

Sildenafil tablets for erectile dysfunction come in three strengths:

• 25 mg - the lowest dose, often recommended for older adults or those taking certain other medicines
• 50 mg - the standard starting dose for most men
• 100 mg - the maximum single dose, used when 50 mg does not provide a sufficient response

All three strengths contain the same active ingredient and work in the same way. The only difference is the amount of sildenafil in each tablet.

Your prescriber will select the most appropriate starting dose based on your medical history, current medications and overall health.

Sildenafil is also available as an oral suspension and as an injection for pulmonary arterial hypertension, but these formulations use different dosing schedules and are not covered here.

According to the BNF, the recommended starting dose for erectile dysfunction is 50 mg, taken approximately one hour before sexual activity.

You should take the tablet with a glass of water, and it can be taken with or without food, although a heavy or high-fat meal may delay the onset of action.

Key points about the 50 mg starting dose:

• Effects typically begin within 30 to 60 minutes
• The medicine remains active for approximately 4 to 6 hours
• You should not take more than one dose per day
• Sexual stimulation is still required for the medicine to work

If 50 mg produces a satisfactory result with acceptable side effects, there is no need to change the dose. Many men find that 50 mg is effective long-term.

However, your prescriber may recommend starting at 25 mg if you have certain risk factors.

Dose adjustment should always be guided by your prescriber. The BNF advises that the dose may be adjusted within the range of 25 mg to 100 mg based on individual response.

When a lower dose (25 mg) may be appropriate:

• Age 65 years or over, as clearance of sildenafil may be reduced
• Significant hepatic impairment (e.g. cirrhosis)
• Severe renal impairment (creatinine clearance below 30 mL/min)
• Concomitant use of CYP3A4 inhibitors such as erythromycin, ketoconazole or ritonavir
• Concomitant use of alpha-blockers for benign prostatic hyperplasia

When an increase to 100 mg may be considered:

• 50 mg has been tried on several occasions (at least 4 to 8 attempts) without adequate effect
• The 50 mg dose was well tolerated with minimal side effects
• No contraindications to a higher dose exist

Never increase your dose without consulting your prescriber. If 100 mg is ineffective, alternative treatments should be explored rather than exceeding the maximum dose.

Getting the timing right can make a meaningful difference to how well sildenafil works.

Timing:

• Take sildenafil approximately one hour before planned sexual activity
• Some men notice effects within 30 minutes; for others it may take up to 60 minutes
• The window of effectiveness lasts roughly 4 to 6 hours, though this does not mean you will have an erection for that duration

Food:

• Sildenafil can be taken on an empty stomach or with food
• A high-fat meal (such as a fry-up or takeaway) may delay absorption by up to one hour
• A lighter meal will have less impact on onset time

Alcohol:

• Moderate alcohol intake is unlikely to cause significant problems, but excessive drinking can worsen erectile dysfunction and increase the risk of side effects such as dizziness and low blood pressure
• The NHS advises keeping alcohol consumption within recommended limits when taking sildenafil

For best results, consider taking sildenafil on a relatively empty stomach and limiting alcohol on the occasions you use it.

Certain groups of patients require extra care with sildenafil dosing.

Older adults (65 years and over):

Plasma levels of sildenafil are approximately 40% higher in those aged over 65 compared with younger adults.

A starting dose of 25 mg is therefore commonly recommended, with upward adjustment only if needed and tolerated.

Hepatic impairment:

Sildenafil is metabolised primarily by the liver. In patients with hepatic impairment (e.g. Child-Pugh class A or B cirrhosis), clearance is reduced and a 25 mg starting dose is advised.

Sildenafil is not recommended in severe hepatic impairment.

Renal impairment:

For mild to moderate renal impairment, no dose adjustment is necessary. In severe renal impairment (creatinine clearance below 30 mL/min), a 25 mg starting dose should be considered.

Patients on interacting medicines:

If you are taking a potent CYP3A4 inhibitor, your prescriber should consider a maximum dose of 25 mg. The BNF provides specific guidance on these interactions.

Always inform your prescriber of all medicines you take, including over-the-counter remedies and herbal supplements.

Following dosing guidelines carefully helps to ensure both safety and effectiveness.

• Never exceed 100 mg in 24 hours. Taking more than the maximum dose increases the risk of serious side effects without improving efficacy.
• Do not take sildenafil with nitrates (such as glyceryl trinitrate or isosorbide mononitrate). The combination can cause a dangerous drop in blood pressure.
• Avoid using sildenafil with other PDE5 inhibitors such as tadalafil or vardenafil.
• Seek medical attention if you experience an erection lasting longer than 4 hours (priapism), sudden vision loss or sudden hearing loss.
• Report side effects to your prescriber. Common side effects include headache, flushing, nasal congestion and dyspepsia. Most are dose-related and may improve with a lower dose.

If you are unsure whether sildenafil is appropriate for you or need advice on dosing, speak with your GP or pharmacist.

The sildenafil NHS information page provides further detail on prescribing and availability.