Penegra 50 mg should be avoided or used only under strict medical supervision when taken with certain medications due to the risk of serious drug interactions, especially dangerous drops in blood pressure. It must never be combined with nitrate medicines such as nitroglycerin, isosorbide dinitrate, or isosorbide mononitrate, which are commonly prescribed for chest pain (angina). The combination can cause a sudden and severe fall in blood pressure, leading to fainting, heart attack, or stroke. Similarly, it should not be Penegra 50 mg with riociguat, a drug used for pulmonary hypertension, as this also significantly increases hypotension risk. Caution is required when Penegra 50 mg is taken with alpha-blockers (like tamsulosin, doxazosin, or prazosin), which are used for high blood pressure or prostate enlargement. Together, they may cause dizziness, lightheadedness, or fainting due to additive blood pressure lowering effects. Doctors may adjust doses or timing if both are necessary. Strong CYP3A4 enzyme inhibitors such as ritonavir, ketoconazole, itraconazole, or erythromycin can increase sildenafil levels in the blood, raising the risk of side effects like headache, flushing, and low blood pressure. Dose adjustment is usually required.