You are generally able to donate blood if you are fit and healthy, weigh between 50kg and 160kg, and are between 17 and 66 years old. Some medications and health conditions may disqualify you, so check with a doctor. Common side effects of donation include bruising, dizziness, and weakness that subside within a few hours or days as your body replaces the donated blood cells and plasma. Regular, safe blood donation may provide health benefits like reduced risk of heart disease and weight loss from burned calories.