Vidalista 20 contains tadalafil 20 mg, a PDE-5 inhibitor used for erectile dysfunction. Back pain and muscle aches are recognized side effects of tadalafil and may occur because of changes in blood flow and effects on muscle tissues. Typical features of tadalafil-related back pain: It may appear 12–24 hours after taking the medicine. It is usually mild to moderate and often improves within 1–2 days. It may occur along with muscle aches or body discomfort. Seek medical advice promptly if: Back pain is severe, persistent, or unusual for you. You have weakness, numbness, loss of bladder/bowel control, fever, or other concerning symptoms. You develop chest pain, severe dizziness, sudden vision/hearing changes, or an erection lasting more than 4 hours. If you tell me when the back pain started after taking Vidalista 20 and whether you have taken tadalafil before, I can help you judge whether it sounds like a likely side effect.