Vidalista 80 mg, which contains tadalafil, can sometimes cause back pain as a side effect. This is a known and relatively common side effect of PDE5 inhibitors like tadalafil (the active ingredient in Vidalista). The exact mechanism behind this back pain isn't fully understood, but there are a few potential reasons why it might occur:

Increased Blood Flow: Vidalista 80 mg works by relaxing the blood vessels and increasing blood flow to certain areas of the body, including the penis. This can lead to changes in blood flow dynamics that might affect muscles and tissues, particularly in the lower back, resulting in discomfort or pain.

Muscle Relaxation: PDE5 inhibitors like tadalafil can also relax smooth muscles throughout the body, not just in the blood vessels. This may extend to the muscles in the lower back, causing muscle aches or stiffness in some individuals.

Changes in Circulation: The medication can lead to changes in how blood circulates, which might affect the back muscles, ligaments, and joints, especially if you're already prone to muscle tightness or strain.

Dehydration: Some people may experience mild dehydration as a side effect of taking tadalafil, which can lead to muscle cramps and discomfort, including back pain.