Starting ED treatment

Advice for those considering using erectile dysfunction (ED) tablets on prescription for the first time.

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Using ED tablets for the first time

Trial of therapy advice

Start with a low dose, and try medication repeatedly at a low dose to start with.

Find a tablet that works well and take the lowest dose which is effective.

Men who are prone to low blood pressure may feel lightheaded or dizzy after taking medication. This is rare. A few hours after taking a tablet for the first time, as a precaution, avoid situations where it is not possible to sit or lie down.


Viagra and sildenafil

Viagra lost its exclusive patent in the UK in June 2103. Viagra is now available legally in the UK under the name sildenafil. Sildenafil is sometimes also known as 'generic Viagra' or 'generic sildenafil'.

There are three strengths of Viagra/sildenafil tablets: 25mg, 50mg and 100mg. Most men should start with 50mg tablets.


If 50mg tablets do not work after trying them four times, and they are not causing side effects, the dose should be increased to 100mg. The maximum should be tried on eight separate occasions before deciding it is not effective.

Viagra/sildenafil needs to be taken at least 45 minutes and preferably one hour before sex. Sexual stimulation is necessary for an erection.

Low cost generic sildenafil became available June 2013.



Cialis comes in four strengths: 2.5mg, 5mg, 10mg and 20mg.

The usual starting dose of Cialis is one 10mg tablet taken between 30 minutes and 12 hours before it is needed. This can be increased to a maximum of 20mg as a single dose or reduced to 5mg in response to treatment.

Cialis will continue to work for up to 24 hours. It should not be taken more than once a day or more than twice a week (see below low dose Cialis).

Cialis should be tried on numerous separate occasions before deciding it is ineffective. Sexual stimulation is required for an erection. Cialis will not cause erections without it. The effectiveness of Cialis is not altered by food.

Low dose Cialis

Men who need Cialis more than twice a week should take a daily tablet of 2.5mg or 5mg. This daily dose is likely to be effective and will not lead to a build-up of Cialis.



There are three strengths of Levitra: 5mg, 10mg and 20mg. Most men should start with a single 10mg tablet.

If 10mg is ineffective the dose may be increased to a maximum of 20mg. If 10mg causes side effects the dose should be decreased to 5mg.

Levitra should be taken about 25 minutes to one hour before attempting intercourse. It can be taken with or without food. Its effect may be delayed if taken with meals high in fat.

It should be tried on multiple separate occasions before deciding it is ineffective. Levitra will not work unless arousal is present.



The recommended dose is 100mg taken as needed approximately 15-30 minutes before sexual activity. Based on individual efficacy and tolerability, the dose may be increased to a maximum dose of 200mg or decreased to 50mg. The maximum recommended dosing frequency is once per day. Sexual stimulation is required for a response to treatment.

Onset of action may be delayed up to 1.5 hours, if taken on a full stomach.

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Authored 19 February 2011 by Dr Tony Steele, MB ChB

Reviewed 14 November 2016 by Dr B. Babor, MB ChB

Last edited 16 November 2016