The dose should be taken at least 30 minutes before intended intercourse, and it may produce an erection in response to sexual stimulation for up to 36 hours after taking the dose.

Warning!
- Unless your doctor or pharmacist tells you otherwise, you should avoid drinking grapefruit juice while taking this medicine, as it may increase the level of this medicine in your blood and hence increase the risk of side effects.

- If your erection lasts longer than 4 hours (priapism), consult a doctor immediately. Treatment of this condition should not be delayed more than 6 hours, as this can cause damage to the erectile tissue in the penis and irreversible erectile dysfunction.

- This medicine may cause dizziness and so may affect your ability to drive or operate machinery safely. Do not drive or operate machinery until you know how this medicine affects you and you are sure it won't affect your performance.

- If this medicine is taken with alcohol there is an increased risk of a drop in blood pressure that might make you feel dizzy. In addition, alcohol can impair sexual performance.

- This medicine should not be taken more than once a day, and it is strongly recommended that you don't use it every day. This is because the long-term safety of using this medicine every day for long periods of time has not been established, and also because the effect usually lasts for longer than one day.

Use with caution in:

- Decreased kidney function
- Decreased liver function
- Disease involving the heart and blood vessels (cardiovascular disease)
- Conditions such as sickle cell disease, bone cancer or leukaemia in which there is an increased risk of prolonged erections (priapism)
- Physical abnormality of the penis, such as severe curvature, scarring or Peyronie's disease
Not to be used in:

- Women
- Children and adolescents under 18 years of age
- Conditions in which sexual activity is not advisable, for example severe heart disorders
- Angina not well controlled by medical treatment (unstable angina)
- People with angina that occurs during sex
- People who have had a heart attack in the last three months
- People who have had a stroke in the last six months
- People with mild to severe heart failure in the last six months
- Abnormal heart beats (arrhythmias) not controlled by treatment
- Uncontrolled high blood pressure (hypertension)
- Low blood pressure (hypotension)
- Rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption
- People taking any form of nitrate medications, eg glyceryl trinitrate
- This medicine is not recommended for people who have ever experienced an eye condition called non-arteritic anterior ischemic optic neuropathy (NAION). This condition causes a sudden, partial decrease or loss of vision in one or both eyes due to damage to the optic nerve. It can be temporary or permanent. Talk to your doctor if you have ever experienced this.

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

Side effects:

- Headache
- Indigestion (dyspepsia)
- Dizziness
- Flushing
- Nasal congestion
- Back pain
- Pain in the muscles (myalgia)
- Eye pain
- Red eye due to excess blood supply (hyperaemia)
- Swelling of the eyelids
- Visual disturbances
- High blood pressure (hypertension)
- Low blood pressure (hypotension)
- Fainting (syncope)
- Chest pain
- Awareness of your heart beat (palpitations)
- Increased heart rate (tachycardia)
- Sweating
- Prolonged or painful erections

How can this medicine affect other medicines?

Tadalafil must not be taken with any form of nitrate medication, as this combination can produce a severe drop in blood pressure that can cause dizziness, fainting, or even a heart attack. Nitrate medications include the following:

- Glyceryl trinitrate, Isosorbide mononitrate, Isosorbide dinitrate, used for angina or heart failure
- Nicorandil
- Amyl nitrate (also known as 'poppers').

If Tadalafil is taken by people who are taking medicines for high blood pressure (antihypertensives), the combination may potentially cause an extra drop in blood pressure. This is unlikely to be significant, but you should be aware that if it does occur it may make you feel dizzy. This is more likely to occur in people taking alpha blocker medicines such as Doxazosin, some of which are used to treat an enlarged prostate gland as well as high blood pressure. Tadalafil is therefore not recommended for men taking alpha blockers.

The use of Tadalafil with other treatments for erectile dysfunction is not recommended, as the safety of such combinations has not yet been established.

The following medicines may increase the blood level of Tadalafil, which could increase the risk of side effects:

- The antifungal medicines ketoconazole and itraconazole
- The antibiotic medicines Clarithromycin and Erythromycin
- The HIV protease inhibitors Ritonavir and Saquinavir.

The following medicines may decrease the blood level of Tadalafil:

- Rifampicin
- Phenobarbital
- Phenytoin
- Carbamazepine

If Tadalafil is taken by people taking Theophylline there may be a small increase in heart rate. This is unlikely to be significant, but you should tell your doctor if you are taking Theophylline.

Tadalafil is also known as Apcalis, Cidect, Erectalis, Forzest, Cialis, Tadacip, Tadafil, Tadalis, Tadamax, Tadil, Tadora ...