Tadalafil (the active ingredient in Tadalista 20) can interact with several medications, and some of these interactions can be serious. The most important interaction is with nitrates, such as nitroglycerin, isosorbide dinitrate, or isosorbide mononitrate. Combining tadalafil with nitrates can cause a dangerous drop in blood pressure, leading to dizziness, fainting, heart attack, or stroke risk. This combination is strictly contraindicated. Another major group includes alpha-blockers like tamsulosin, doxazosin, or terazosin, which are used for prostate enlargement or high blood pressure. When taken together, they may also cause low blood pressure, especially when starting therapy or adjusting doses. Tadalafil is metabolized mainly by the liver enzyme CYP3A4, so drugs that affect this enzyme can change tadalafil levels: CYP3A4 inhibitors (increase tadalafil levels and side effects): Ketoconazole Itraconazole Ritonavir Clarithromycin Erythromycin Grapefruit juice (can moderately increase levels) CYP3A4 inducers (reduce effectiveness): Rifampin Carbamazepine Phenytoin Phenobarbital Other important interactions: Antihypertensive drugs (blood pressure medications): may increase the risk of hypotension Alcohol: can worsen dizziness, low blood pressure, and side effects Riociguat (for pulmonary hypertension): contraindicated due to severe hypotension risk Because of these interactions, Tadalista 20 should only be used under medical supervision, especially if you are already taking heart, blood pressure, or prostate medications.