Tamoxifen This drug was originally licensed for the treatment of breast cancer. Sildenafil or Viagra Viagra started life as a drug to treat hypertension, or high blood pressure. Only 10 per cent of new drugs make it through trials, they often take 10 years, and cost 10 billion pounds. But now, the repurposing of drugs is becoming far more sophisticated. But during trials, doctors noticed it worked on HIV.Viagra is only available with a prescription in the United States, Canada, and most other countries. Viagra is sold under the generic name sildenafil, which is also only available . This physiological effect led Pfizer to market sildenafil in for erectile dysfunction, under the brand name Viagra, generating peak annual sales in excess of $2 billion. Drugs including Viagra and Cialis lead to an average improvement of 4 to 8 points on the scale used by researchers and clinicians. The team behind the new study suggests that .