Back pain is listed as a potential side effect of Vigora 100 mg, which contains sildenafil citrate, a phosphodiesterase type 5 (PDE5) inhibitor used to treat erectile dysfunction (ED) in men. While not everyone experiences this side effect, some individuals may notice back pain after taking Vigora 100 mg or other medications in the same class. Here are some reasons why back pain may occur as a side effect of Vigora 100 mg:

1. Muscle Relaxation: Sildenafil, the active ingredient in Vigora 100mg, works by inhibiting the enzyme phosphodiesterase type 5 (PDE5), which leads to increased blood flow to the penis and relaxation of smooth muscle tissue in the blood vessels. This relaxation of smooth muscle tissue can also affect other parts of the body, including muscles in the back, leading to muscle relaxation and potential discomfort.
   
2. Vasodilation: Sildenafil can cause vasodilation (widening of blood vessels) not only in the penis but also throughout the body. While this vasodilation is desirable in the treatment of ED, it can also lead to changes in blood flow to various areas, potentially contributing to sensations of discomfort or pain, including back pain.
   
3. Central Nervous System Effects: Sildenafil can also affect the central nervous system, which may influence pain perception and sensitivity. Changes in neurotransmitter activity or modulation of pain pathways could potentially contribute to the experience of back pain as a side effect of Vigora 100 mg.
   
4. Individual Sensitivity: Some individuals may be more sensitive to the effects of sildenafil or may experience side effects more prominently than others. Factors such as age, overall health, pre-existing medical conditions, and concurrent medication use can influence an individual's response to sildenafil and the likelihood of experiencing back pain or other side effects.
   
5. Postural Changes: In some cases, individuals may experience changes in posture or muscle tension as a result of sexual activity or arousal facilitated by Vigora 100 mg. These postural changes could potentially contribute to back pain or discomfort.
   

It's important to note that while back pain is listed as a potential side effect of Vigora 100 mg, not everyone will experience this symptom. If back pain persists or becomes severe or concerning after taking Vigora 100 mg, it's essential to consult with a healthcare provider for further evaluation and guidance. Additionally, individuals with a history of back problems or chronic back pain should discuss potential risks and benefits with their healthcare provider before using Vigora 100 mg or similar medications for ED.