by kapil
(india)
QUESTION: I have type 2 diabetes and am new to insulin. In India, I see insulin labelled 40 IU and 100 IU. Which is the better dose, and why?
U-40 and U-100 are insulin concentrations—not competing doses. U-40 contains 40 units per millilitre, while U-100 contains 100 units per millilitre. Neither is automatically better. The prescribed number of units should be individualized, and the vial must be used with the matching U-40 or U-100 syringe. Mixing them can cause a 2.5-fold dosing error, severe hypoglycemia, or dangerously high glucose.
Answer by Dr. Albana Greca, MD, MMedSc
Hi Kapil,
The label is easy to misunderstand. “40 IU” or “100 IU” usually refers to how concentrated the insulin is in each millilitre of liquid. It does not mean that you should inject 40 or 100 units.
The “U” means units. IU, or international units, is also used on some labels. For prescriptions and spoken instructions, writing the full word units is safer than abbreviations that can be misread.
U-100 contains more insulin in the same volume, but one correctly measured insulin unit has the same glucose-lowering activity. For example, a prescribed dose of 10 units is still 10 units:
The liquid volume differs, not the intended number of insulin units. Do not calculate the volume yourself unless a diabetes professional has trained you and verified the device.
India may use both U-40 and U-100 insulin and syringes. Check the concentration printed on the vial and the syringe before every injection:
A mismatch is dangerous. If U-100 insulin is drawn to the 10-unit mark on a U-40 syringe, the person receives 25 actual units. If U-40 insulin is drawn to the 10-unit mark on a U-100 syringe, only 4 actual units are delivered.
Do not rely only on syringe-cap color because packaging can differ. Read the concentration marking. Never use a standard millilitre syringe for insulin unless a clinician has provided specific supervised instructions.
With a compatible prefilled pen or cartridge-and-pen system, the dose window displays the number of insulin units to inject. The device accounts for its concentration. Dial the prescribed units; do not convert them into millilitres.
Never withdraw insulin from a pen or cartridge with a syringe. This bypasses the pen's dosing system and may cause a serious overdose, especially with concentrated insulin.
There is no universal dose for type 2 diabetes. The clinician considers body weight, fasting and after-meal glucose, HbA1c, kidney and liver function, food intake, activity, other diabetes medicines, and hypoglycemia risk.
When basal insulin is appropriate, clinicians may estimate an initial dose from body weight and the severity of hyperglycemia, then adjust gradually from glucose patterns. This is not a formula to use without supervision. Neither 40 units nor 100 units is a standard starting dose for everyone.
Using insulin does not mean that diet, exercise, or tablets have “failed.” Type 2 diabetes changes over time, and the pancreas may no longer produce enough insulin. Insulin may also be needed temporarily during severe illness, surgery, pregnancy, steroid treatment, or marked hyperglycemia.
Current care also considers medicines that support weight, heart, and kidney health. The complete treatment plan should be reviewed rather than simply increasing insulin whenever glucose is high.
Ask a doctor, diabetes educator, nurse, or pharmacist to watch you prepare and inject a dose. Confirm:
Review our insulin treatment guide and use a blood sugar log during dose adjustment.
Check glucose immediately and contact the prescribing clinician, pharmacist, poison service, or emergency department for individualized instructions. The risk depends on which mismatch occurred, the intended dose, insulin type, injection time, meals, kidney function, and current glucose.
Do not try to correct a suspected overdose by guessing how much food to eat, and do not take extra insulin to correct a suspected underdose without professional advice.
Seek emergency help for unconsciousness, seizure, inability to swallow, severe confusion, or a low that does not improve after treatment. If an insulin overdose may have occurred, obtain urgent advice even when glucose is initially normal because some insulins can cause delayed or prolonged hypoglycemia. Seek urgent care for persistent severe hyperglycemia, vomiting, difficult breathing, dehydration, confusion, or ketones.
Do not choose between U-40 and U-100 by yourself. Ask the prescriber to write the insulin name, concentration, device, number of units, and timing clearly. Before leaving the pharmacy, compare the vial or pen with the prescription and confirm that any syringe has the same U-number.
Educational safety note: This answer is for general diabetes education only. It does not replace hands-on insulin training or an individualized prescription. Do not start, stop, switch, dilute, convert, or change an insulin dose or delivery device without guidance from a qualified healthcare professional.
Last reviewed: July 2026.
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