💉 Insulin Therapy for Diabetes: Types, Regimens, and What to Expect

For many people, hearing the word “insulin” brings anxiety — fear of needles, fear of weight gain, or the feeling that they have failed to manage their diabetes. But insulin is not a punishment; it is simply a replacement for what the body can no longer make on its own. Dr. Ravi Sishir Reddy explains the different types of insulin, how they are used in combination (basal‑bolus therapy), and why starting insulin can be a positive turning point toward better health.

1. What Is Insulin and Who Needs It?

Insulin is a hormone produced by the beta cells of the pancreas. It allows glucose to enter cells for energy. In Type 1 diabetes, the body produces virtually no insulin, so exogenous insulin is necessary from diagnosis. In Type 2 diabetes, the body initially produces insulin but is resistant to its effects. Over time, the beta cells become exhausted and insulin production declines. When oral medications and other injectables (like GLP‑1 agonists) are no longer sufficient, insulin is introduced. Starting insulin early, when needed, actually preserves remaining beta‑cell function and reduces long‑term complications.

2. Types of Insulin at a Glance

Insulin is classified by how quickly it starts working, when it peaks, and how long it lasts. The main categories are:

• Rapid‑acting insulin: Starts working in 10‑15 minutes, peaks in 1‑2 hours, and lasts 3‑5 hours. Examples: insulin lispro (Humalog), insulin aspart (NovoLog), insulin glulisine (Apidra). Taken just before or immediately after meals to cover the carbohydrate intake (bolus).
• Short‑acting (Regular) insulin: Starts in 30 minutes, peaks in 2‑4 hours, lasts 5‑8 hours. Example: human regular insulin (Actrapid). Taken 30 minutes before a meal.
• Intermediate‑acting insulin: Starts in 1‑2 hours, peaks in 4‑12 hours, and lasts 12‑18 hours. Example: NPH (isophane) insulin. Often used twice daily to provide basal coverage, though it has a variable peak.
• Long‑acting insulin (basal): Provides a steady, peak‑less release over 20‑24 hours or more. Examples: insulin glargine (Lantus, Toujeo), insulin detemir (Levemir), and the ultra‑long‑acting insulin degludec (Tresiba, lasts over 42 hours). Taken once daily to mimic the background insulin secretion of a healthy pancreas.
• Pre‑mixed insulin: A fixed combination of a rapid‑ or short‑acting insulin with an intermediate‑acting insulin. Examples: 70/30 (70% NPH, 30% regular), or analogue mixes (aspart protamine/aspart). Convenient (fewer injections) but less flexible because both basal and meal coverage are fixed.

3. The Basal‑Bolus Regimen: Mimicking the Pancreas

The most physiological way to use insulin is the basal‑bolus regimen, which attempts to replicate what a normal pancreas does. It consists of:

• Basal insulin: One injection of long‑acting insulin (glargine, detemir, or degludec) usually at bedtime or the same time each day. This covers the body’s background insulin needs between meals and overnight.
• Bolus insulin: A rapid‑acting insulin injection before each main meal (breakfast, lunch, dinner) to cover the rise in glucose from food. The dose may be calculated based on the amount of carbohydrate in the meal (carb counting) or a fixed dose prescribed by the doctor.

For example, a typical basal‑bolus regimen might be:
• 8 a.m.: rapid‑acting insulin before breakfast
• 1 p.m.: rapid‑acting insulin before lunch
• 8 p.m.: rapid‑acting insulin before dinner
• 10 p.m.: long‑acting insulin at bedtime

This approach provides the greatest flexibility — you can vary meal timing and content — but requires multiple daily injections and frequent blood glucose checks.

4. Other Insulin Regimens

• Basal‑only: A single injection of long‑acting insulin, often combined with oral medications. This is a common starting regimen in Type 2 diabetes when oral agents are not enough.
• Twice‑daily pre‑mixed: Pre‑mixed insulin before breakfast and dinner. Simpler, but less flexible. Requires consistent meal timing and carbohydrate intake.
• Continuous subcutaneous insulin infusion (CSII) / insulin pump: A pump delivers a continuous basal rate of rapid‑acting insulin, with the user manually giving boluses for meals. This provides the tightest control but requires significant commitment and education.

5. How Is the Insulin Dose Decided?

Insulin dosing is highly individualised. The starting dose is based on body weight, estimated beta‑cell function, and current blood sugar levels. A common starting dose in Type 2 diabetes is about 0.1‑0.2 units per kilogram per day for basal insulin. Over time, doses are adjusted based on fasting and post‑meal glucose readings, HbA1c, and the occurrence of hypoglycemia. Dr. Reddy emphasises that insulin therapy requires an active partnership between the patient and the doctor — it’s not “set and forget.”

6. The Most Important Risk: Hypoglycemia

The main risk of insulin therapy is hypoglycemia (low blood sugar) — generally defined as a glucose level below 70 mg/dL. It can occur if the insulin dose is too high, a meal is skipped or delayed, or after unplanned exercise. Symptoms include shakiness, sweating, palpitations, confusion, and in severe cases, seizures or unconsciousness. Every patient on insulin must:

• Know the early warning signs of low blood sugar.
• Carry fast‑acting glucose (glucose tablets, a small juice box, or sweet) at all times.
• Check blood sugar before driving.
• Have a glucagon emergency kit at home and ensure family members know how to use it.

7. Weight Gain, Injection Site Issues, and Other Concerns

• Weight gain: Insulin promotes the storage of glucose as fat. Combined with the need to eat to avoid hypoglycemia, weight gain of 2‑5 kg is common after starting insulin. This can be mitigated by a healthy diet, regular exercise, and using insulin in combination with drugs that promote weight loss (like GLP‑1 agonists or SGLT2 inhibitors).
• Lipohypertrophy: Lumpy, thickened areas of fat under the skin caused by repeated injections in the same site. Rotating injection sites regularly prevents this and ensures consistent insulin absorption.
• Injection pain: Modern insulin needles are extremely fine and short, and most people are surprised at how little they feel.

8. Practical Tips for Insulin Users

• Store insulin correctly: Unopened vials/pens in the fridge (2‑8°C). The pen or vial in use can be kept at room temperature (below 30°C) for about a month. Never freeze insulin.
• Rotate injection sites: Use different areas of the abdomen, thighs, or upper arms. Stay 2‑3 cm away from the navel and avoid the same spot repeatedly.
• Monitor glucose as recommended: At least before meals and bedtime, or more frequently if adjusting doses.
• Don't skip meals after injecting rapid‑acting insulin. If you are sick and cannot eat, contact your doctor for sick‑day guidance; you still need basal insulin, but bolus doses may need adjustment.
• Carry a medical ID identifying you as insulin‑dependent.