The mechanism of action of Malegra 50 mg involves inhibiting the enzyme PDE5, which regulates blood flow in the penis. By blocking PDE5, sildenafil citrate promotes the relaxation of smooth muscles and dilation of blood vessels in the penis, allowing for increased blood flow and the achievement of an erection when sexually aroused. The effects of Malegra 50 mg typically begin within 30 to 60 minutes after ingestion and can last for up to four hours. It is important to note that sexual stimulation is necessary for the medication to work effectively.