Common ones include: Flushing of the skin. The GPO employs a different procedure to produce sildenafil, so the organisation insists it is not violating any international patent law. Generic versions of sildenafil, vardenafil and tadalafil are available. As the anti-erectile dysfunction drug is categorised by the FDA as falling into a specially controlled drug group, patients still need a prescription to buy it, and can obtain the drug at around FDA-certified pharmacies as well as public and private hospitals and clinics nationwide. This medication is taken with or without food an hour before sex.Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. This boosts blood flow and helps you get an erection from sexual activity. How oral medicines differ. 66 helpful votes. 5. Re: Kamagra/viagra. 6 years ago. Save. Yea was gonna say if you aint got a prescription you wont get any Viagra at a pharmacy. Same goes for Cialis. So if you haven’t then you have to buy off the street. Sukhimvit road anywhere from soi 4 down to soi cowboy you will find a stall or two selling kamagra. Putting some proverbial wood in one’s pencil just got a bit cheaper for men in Thailand. Yep, Thailand’s Government Pharmaceutical Organisation (GPO) will launch its own brand of .