You can safely take Viagra with caffeine as no interactions will occur when Viagra and Caffeine are taken together.
However you might experience some slight side effects but they usually are not serious.
Viagra for men and similar ED drugs like Cialis (tadalafil) and Levitra (vardenafil) work by helping to relax muscles and arteries inside the penis, which helps more blood reach the penis. When aroused and only when aroused the combination of relaxation and increased blood flow helps fill the penis with blood.
Does Viagra keep you hard after coming?
Strictly speaking, no, Viagra does not keep you hard after ejaculation.
Nevertheless, studies suggest that it could reduce your refractory period, and it will work for 4-6 hours, meaning that once your refractory period's over, you should have no trouble getting another erection.
When you're sexually stimulated, Viagra can make your erect penis larger than usual.
This is because the drug increases the amount of blood flow to your penis, increasing its size.
But a rare side effect of Viagra is swelling of your genitals, including your penis.