Cialis and Viagra both work by increasing free NO (Nitric Oxide) in the bloodstream. I work in pharma research and we can mimic the same action using a topical cream that releases NO from a different reaction - that of sodium nitrite and a tripeptide compound mixed together. The formulation was initially going to be used for a replacement for Viagra, but the regulatory hurdles are immense.
It is also an incredible antibiotic- I have used it to stop a skin infection caused by a rusty nail while dismantling an old deck- it literally stopped the infection in 2 hours. You also notice that wounds heal much faster when using this cream- it's like magic.
You can increase NO in the bloodstream naturally, eating pomegranate seeds, watermelons (!) and 70-80% dark chocolate, among other foods. It's not going to be as powerful as drugs but you will increase the level of NO in circulation without any side effects.