Insulin has been used to treat diabetes for 100 years. Low blood sugar is a side effect of insulin that still worries people with diabetes, their families, friends, and care providers. Low blood sugar is also called hypoglycemia. Hypoglycemia can be unpleasant and dangerous. Repeated hypoglycemia causes lasting harm. This may include confusion, fainting, coma, seizures, memory loss, fear, and death. It may lead to losing a driver’s license, missing work, family stress, and relationship problems. Repeated hypoglycemia can affect brain development in children and dementia in older people. Diabetes therapies aim to control blood sugar levels and reduce hypoglycemia.