Penegra 50 mg can cause back pain because it contains sildenafil, a medicine used to treat erectile dysfunction (ED). Back pain is a recognised side effect of sildenafil, although it is less common than headache or facial flushing. Why does it happen? Blood vessel effects: Sildenafil relaxes blood vessels by inhibiting the PDE5 enzyme. Its effects on the body may contribute to muscle discomfort in some people. Muscle aches: Some people experience muscle pain or general body aches after taking sildenafil. Individual sensitivity: Side effects vary depending on your sensitivity to the medicine, dose, and other medications you take. When can back pain start and stop? Onset: It may begin within a few hours of taking the tablet. Duration: It often improves as the medication wears off, usually within a day, although it can last longer. What should you do? Rest and avoid strenuous activity while you have discomfort. Do not take another dose until the pain has settled and you have considered discussing it with a healthcare professional. Seek urgent medical care if the pain is severe, accompanied by chest pain or difficulty breathing, or associated with weakness, numbness, or trouble urinating.