Actrapid 100 IU/ml Flexpen is a short-acting insulin used to treat type 1 and type 2 diabetes mellitus. It is used together with a healthy diet and regular exercise to control blood sugar levels after meals. This helps to prevent serious complications of diabetes like kidney damage and blindness. Actrapid 100 IU/ml Flexpen is normally prescribed along with a long-acting type of insulin or other diabetes medicines. Your doctor or nurse will teach you the correct way of injecting it under the skin. It should be taken 20-30 minutes before a meal. Do not stop taking it unless your doctor tells you to. It is only a part of the treatment program that should also include a healthy diet, regular exercise, and weight reduction as advised by your doctor. Check your blood sugar levels regularly, keep track of your results and share them with your doctor. This is very important to work out the correct dose of the medicine for you. The most common side effect of this medicine is low blood sugar levels (hypoglycemia). It may be seen if you do not eat right after a dose of this fast-acting insulin. To prevent this, it is important to always inject only the correct dose of medicine, have regular meals, and monitor your blood sugar levels regularly. Drinking excessive alcohol can also lead to a fall in your blood sugar levels. Other side effects include reactions at the injection site like redness or swelling. Some people gain weight while taking insulin. Do not use this medicine when you have low blood sugar levels (hypoglycemia). Tell your doctor if you have ever had kidney, liver, or heart problems before starting treatment. Pregnant or breastfeeding women should also consult their doctor as the dose may need to be changed.