Cialis reaches its maximum effectiveness two hours after you take it. When a man is sexually stimulated, his body’s normal response is to increase blood flow to his penis to produce an erection. Which Works Faster? However, eating food, particularly high-fat food, can reduce the effectiveness of Viagra. Men with BPH usually have difficulty urinating, a decreased flow of urination, hesitation at the beginning of urination, and a need to get up at night to urinate. Nitrate-mediated vasodilation is markedly exaggerated and prolonged in the presence of PDE-5 inhibitors.Cialis (tadalafil) is a type of PDE5 inhibitor that the Food and Drug Administration approved in Like other PDE5 inhibitors, it increases blood flow to the penis. There are two different ways to take Cialis: as needed or daily. If you take the pill daily, the medication stays in your system constantly. · Tadalafil is used to treat men who have erectile dysfunction (also called sexual impotence). Tadalafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. Drug Interactions. Although certain medicines should not be . Adcirca is the brand name version of tadalafil 20 mg tablets for PAH, and Alyq is its FDA-approved generic version. Adcirca and Alyq can be substituted one for the other because they come in the same strength and dosage form.