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Development of Viagra™
The table shows the main stages in the development
1985 Initial concept Initial concept
In 1985, scientists at Pfizer decided to develop a medicine to treat heart failure and hypertension. They were looking for a medicine that would vasodilates, or "open", arteries, lower blood pressure and reduce strain on the heart. They chose to target the medicine to act on an enzyme found in the wall of blood vessels.
1986 - 1990 Research and Development starts Research and Development
Between 1986 and 1990, hundreds of possible medicines were synthesised and tested in laboratory experiments.

The most promising compound was given the code name UK-92,480. It showed properties that suggested it would be a good medicine to treat angina. Research was redirected to look at this heart disorder.

The medicine was later called Sildenafil and finally renamed Viagra™ (Sildenafil citrate).

1991 Volunteer trials Volunteer trials
In 1991, healthy volunteers took part in clinical trials to test the safety of Viagra™ and how the body metabolised the compound.

These showed that it was safe. In trials over 10 days, the healthy volunteers reported some unexpected side effects. Male volunteers reported more frequent erections after taking the Angina medicine!

1992 Erectile dysfunction Erectile dysfunction
Following the unusual side effects seen in the volunteer trials, researchers switched to looking into using Viagra™ to treat Erectile dysfunction (ED). This serious condition causes psychological and emotional problems that affects many families.

Research into using Viagra™ to treat angina continued but the medicine did not prove powerful enough to be really useful.

1993 - 1996 ED clinical trials start ED clinical trials
'Double-blind, placebo controlled' clinical trials started in 1993 to test how well Viagra™ treated patients with Erectile dysfunction. To make the trials a fair test, neither the patients, nor their doctors, knew if they were receiving the medicine or an inactive placebo

Viagra™ proved to be a great success.

1997 Licence application Licensing
All medicines need to be licensed by the medical authorities before they can be prescribed by doctors. To achieve this, trials must show it is safe and effective. Approval usually takes about 12 months but in the case of Viagra™ it received its license in only 6 months.
1998 Licence approval Viagra™ was given a license
It couold be used in the treatment of erectile dysfunction in 1998. In its first three months, there were 2.9million prescriptions for the medicine.