20 mg is really high dose. For the majority 5 mg Cialis can work. Aspirin can also be used if you never tried Cialis or Viagra. Aspirin has less side effect and you can buy on counter. Aspirin has nearly and relatively the same effect in enlarging blood vessels. That is reason Aspirin is placed in many Firs-aid kits in case some body is having heart attack Aspirin may saves lives. However, Aspirin can also upset stomach or reduce blood pressure. So it must not used in excessive doses.
Important tip: whatever pill you take or not take, have some deep breath before starting to have fun. Remember the biggest and the most important sex organ is your brain and oxygen is brain's fuel.
Note: I am not a doctor. I just wrote what worked and is working for me.