Viagra works best when it is taken on an empty stomach approximately an hour before sex, and it is typically effective for four to six hours. This doesn’t mean you can’t take Viagra with food, because it’s safe to do so. However, some men who have tried taking Viagra both with and without food find that when they take it with a large meal or a meal containing a lot of fat, it takes longer for the drug to be effective.
If you take Viagra and don’t think it’s working as it should, consider whether you have recently eaten heavy or fatty foods. If so, that could be responsible for the seemingly dampened effect.