Pfizer, the original developer of Viagra, is the licensee of Sildenafil Citrate. They have been the sole legitimate supplier and manufacturer of this medication in the USA for a long time. Clearly its an awesome market and pill sales worldwide are astronomical.

In this day and age the world's pharmaceutical companies don't just sit back and watch. They develop parallel products to erode Pfizer's market and attempt to share the lucrative erectile dysfunction remedy market. Pfizer is obviously defending their patent to the death in order to keep the competition out.

Currently Pfizer faces serious competition from two legitimate quarters:-

• GlaxoSmithKline / Bayer who manufacture Levitra® (vardenafil)
  Levitra (or vardenafil) is a PDE-5 inhibitor which works in the same way as Viagra. Inhibiting PDE-5 helps the smooth muscles in the penis to relax, thus increasing blood flow and enabling erection.
  Levitra was approved by FDA in august 2003. Studies have proved that levitra has lesser side effects than viagra and works for longer period of time.
  
  

• Eli Lilly / ICOS consortium who manufacture Cialis™ (tadalafil)
  Cialis(TM) (tadalafil) is an oral PDE5 inhibitor for the treatment of erectile dysfunction (ED). Cialis was launched in the major markets of Europe, Australia and New Zealand the week of February 5th, 2003. And finally, on 21st November, 2003, the U.S. Food and Drug Administration (FDA) approved Eli Lilly & Co. and Icos Corp.'s anti-impotence drug, Cialis. It is commonly called "The Weekend Pill" because its effects stay in the system about 36 hours after consumption. Cialis can be taken about an hour before the sexual activity and can also be mixed with alcohol.

Related articles are here:-
Cialis(TM) (tadalafil) Approval
 

Viagra made in India is safe and trusted for treatment of male erectile dysfunction. There are many cheap versions of Viagra made in India which acts similar to brand name Viagra. Most common names of Viagra made in India are Caverta, Silagra, Kamagra, and Edegra.

Soft Tabs(*) made in India are sublingual capsules for "Quicker Action". SOFT TABS are made with the same active ingredient, Sildenafil Citrate that is used in Viagra made by Pfizer® Pharmaceuticals. They are manufactured to the same quality standards and produce the same results. Soft Tabs capsules dissolve when placed under the tongue and enter the bloodstream immediately, so the effects appear within 15 - 20 minutes.
(*) Capsules cannot be cut.

Caverta: Launched by Ranbaxy, CAVERTA ® is a tablet used to treat erectile dysfunction (impotence) in men. It can help men who have erectile dysfunction get and sustain an erection when they are sexually excited. One does not get an erection just by taking this medicine. CAVERTA ® helps a man with erectile dysfunction get an erection only when he is sexually excited. Caverta is Ranbaxy's brand of Sildenafil Citrate. Ranbaxy is one of India's biggest Pharmaceutical Companies with an annual turnover of $ 764 million.

Penegra: Launched by Zydus Cadila, PENEGRA is a brand name for Sildenafil Citrate, treatment for men with erectile dysfunction (ED). Zydus Cadila is one of India's biggest Pharmaceutical Companies with an annual turnover of $ 400 million, providing total healthcare solutions ranging from formulations, active pharmaceutical ingredients, vaccines, diagnostics, herbals, animal healthcare to cosmeceuticals.

Silagra / Progra(*): Launched by Cipla, Silagra/Progra are a revolutionary medical treatment designed to counter the effects of impotence (ED or Erectile Dysfunction). Silagra/Progra are administered orally in the form of a pill and are only to be taken when you want to have sex. Silagra/Progra are designed to help many men with impotence to maintain an erection when they become sexually aroused (either physically or visually). Silagra and Progra are Cipla's brands of Sildenafil Citrate. More than 65 years old, Cipla is a big Pharmaceutical Company of India with an annual turnover of $ 290 million.
(*) Progra is manufactured by Protec - a division of Cipla.

Edegra: Launched by SunPharma, EDEGRA is a brand name for Sildenafil Citrate. It's a medicine that helps men with erectile dysfunction (ED) have sexual intercourse again. Edegra is Sun Pharma's brand of Sildenafil Citrate. Sun Pharmaceutical Industries Limited has been in existence since 1983. The company has a turnover of more than $100 million per year. It is located in Ahmedabad in India .

Kamagra: Launched by Ajanta Pharmaceutical, KAMAGRA is a brand name for Sildenafil Citrate. It's a medicine that helps men with erectile dysfunction (ED) have sexual intercourse again. Kamagra is Ajanta Pharma's brand of Sildenafil Citrate. Ajanta Pharma Ltd is an Indian Pharmaceutical company based in Mumbai, with a turnover of more than $30 million. This company has eight international joint ventures.