Some of the drugs that can potentially interact with vardenafil include alpha blockers, ritonavir, and indinavir. Drug interactions with vardenafil can (in some cases) lead to an increased chance of fainting or decreased blood pressure. People who are taking nitrates (including recreational drugs called "poppers") should not use vardenafil, and people who drink grapefruit juice may want to avoid grapefruit juice while taking vardenafil.