Insulin Basics: Types, Side Effects and Safe Use Tips

7 min read · Medicines · By the Asthra Health Care team

What insulin is used for

Insulin is a hormone made by the pancreas that moves sugar from the blood into the body's cells for energy. People with type 1 diabetes make little or no insulin and need insulin injections from the time of diagnosis for life. Many people with type 2 diabetes also need insulin when tablets are no longer enough, during serious illness or surgery, or when sugar is very high.

Doctors also use insulin for diabetes during pregnancy, as it is safe for the baby. Starting insulin is not a sign of failure or a last stage of disease. It is simply the most effective way to control sugar when the body cannot make enough of its own.

• Type 1 diabetes, always
• Type 2 diabetes not controlled with tablets
• Diabetes in pregnancy, including gestational diabetes
• Hospital care during illness or surgery

How insulin works and its types

Injected insulin copies the body's own insulin. It lowers blood sugar by helping muscles, fat and the liver take up and store sugar, and by reducing the sugar the liver releases. Different types are designed to work over different lengths of time.

Rapid-acting and short-acting insulins cover meals. Intermediate and long-acting, or basal, insulins give a steady background level through the day and night. Premixed insulins combine both in one injection. Your doctor chooses the type, timing and amount based on your sugar readings, meals and lifestyle. Never change these on your own; insulin is only on a doctor's prescription.

• Rapid-acting and short-acting: for meals
• Intermediate and long-acting (basal): background control
• Premixed: a mix of meal-time and background insulin

Insulin basics side effects: common and serious

The main side effect is low blood sugar, or hypoglycaemia. Warning signs include sweating, shaking, hunger, a fast heartbeat, headache, blurred vision, irritability and confusion. It is more likely after skipping or delaying a meal, extra exercise, alcohol, or taking too much insulin. Severe low sugar can cause fits or unconsciousness.

Other side effects include weight gain, and lumps or dents in the skin from injecting repeatedly in the same spot. These lumps can also stop insulin from being absorbed properly. Mild redness or itching at the injection site can occur. Rarely, allergic reactions or low potassium levels happen.

Who should take extra care with insulin basics

Children, elderly people, people with kidney or liver disease, and those who live alone or have irregular meals are at higher risk of low sugar and need close monitoring. People with reduced vision or hand problems may need help with pens or syringes. Those who drive or work at heights should check sugar before starting.

In pregnancy, insulin needs often change quickly, so frequent review with the doctor is essential. Breastfeeding mothers may also need adjustments. People who fast during festivals or religious observances should plan their insulin with the doctor in advance. Illness with vomiting or poor appetite also changes insulin needs, so ask your doctor for a written sick-day plan.

Insulin basics interactions to know

Other diabetes medicines, especially sulfonylureas like glimepiride, add to the risk of low sugar. Doctors often combine insulin with metformin or other tablets, but that is always their decision. Alcohol can cause delayed low sugar, sometimes overnight. If you drink, never do so on an empty stomach, and check your sugar before sleeping.

Steroids, some water tablets and certain other medicines can raise blood sugar, so insulin needs may go up. Beta-blocker heart medicines can hide the shaking and pounding heart of low sugar. Tell every doctor you see that you take insulin, and let your diabetes doctor know when any new medicine is started.

Storage and injection tips

Store unopened insulin in the refrigerator, not in the freezer, and never let it freeze. The pen or vial in use can usually be kept at room temperature for the time stated on the pack, but Indian summers can be very hot, so keep it away from direct sunlight, kitchen stoves and parked vehicles. Use a cool pouch when travelling. Do not use insulin that looks cloudy when it should be clear, or has clumps.

Inject into the fatty layer of the tummy, thighs or upper arms as taught, and rotate sites to avoid lumps. Use a new needle each time. Check your sugar as advised and keep a record. Always carry glucose tablets or sugar and a card saying you have diabetes.

When to talk to your doctor about insulin basics

See your doctor if you have frequent low sugar, high readings despite insulin, or lumps at injection sites. Seek urgent care for vomiting, fast breathing, drowsiness or confusion, especially in type 1 diabetes, as these can signal dangerous ketoacidosis. Your doctor, diabetes educator or pharmacist can help with any questions about insulin.

This article is general health information, not medical advice. Do not start, stop or combine medicines on your own — always follow your doctor's prescription and ask your pharmacist if unsure.