An overdose of Zenegra 100 mg (which contains sildenafil, the same active ingredient as Viagra) can lead to serious side effects. Some signs and symptoms of a Zenegra overdose may include:

1. Severe Headache – A common side effect of sildenafil, but an overdose can cause more intense headaches.
2. Dizziness or Lightheadedness – This may occur due to a significant drop in blood pressure.
3. Vision Changes – Overdosing may lead to blurred vision, color vision changes (seeing everything with a blue tint), or increased sensitivity to light.
4. Chest Pain or Palpitations – This may indicate strain on the heart or circulatory system.
5. Nausea or Vomiting – Digestive issues can arise from excessive medication.
6. Prolonged or Painful Erection (Priapism) – An erection lasting longer than 4 hours is a medical emergency and requires immediate attention.
7. Shortness of Breath – Difficulty breathing or wheezing may be signs of an overdose affecting the respiratory system.
8. Rash or Skin Reactions – Allergic reactions, such as hives or swelling, may occur.
9. Confusion or Disorientation – Overdosing can affect cognitive function, causing confusion or dizziness.

If you or someone else experiences any of these symptoms after taking Zenegra 100mg, it's important to seek medical attention immediately. Overdose can cause severe health complications, especially if it leads to priapism or cardiovascular issues. Always take medications as prescribed and consult with a healthcare provider before adjusting the dose.