Viagra has been studied in four main studies including 1, men aged 19 to 87 years, where it was compared with placebo a dummy treatment for between 12 and 26 weeks. Viagra is used to treat adult men with erectile dysfunction sometimes called impotence , when they cannot get or keep a sufficiently hard penis erection for satisfactory sexual activity. The medicine can only be obtained with a prescription. The main measure of effectiveness was based on the ability of the men to get and maintain an erection. This was recorded in a special questionnaire completed at home using a scoring system on a five-point scale, where a score of 5 represents the best result. This medicine is authorised for use in the European Union.In the European Union (EU), it is possible to buy medicines online. Patients should only buy medicines from online retailers registered with the national competent authorities in the EU Member States, to reduce the risk of buying sub-standard or falsified medicines. Be aware that German law prohibits the mailing or shipment of drugs, including prescription medicines, to private persons in Germany from the US or other foreign countries. However, if you are carrying prescribed medicine with you while traveling to . Be aware that German law prohibits the mailing or shipment of drugs, including prescription medicines, to private persons in Germany from the US or other foreign countries. .