Viagra or Sildenafil citrate or Revatio is the most widely sold male enhancement drug these days. But there are some side effects to this wonder drug. This includes headache, flushing, dyspepsia, nasal congestion and impaired vision, including photophobia and blurred vision.. There are also some new ones available – Cialis (tadalafil) and Levitra (vardenafil). But these too have side effects. So I think its better you try out some natural male enhancement products which have much less side effects.