Insulin’s main risk is low blood sugar, or hypoglycaemia. It is the effect worth understanding thoroughly, because it can develop quickly, it is easy to treat when recognised early, and it becomes dangerous when it is not.
Insulin doses are highly individual. This page describes general safety information and does not replace the plan agreed with your diabetes team.
Common side effects during long-term use
Low blood sugar is the most common. Early symptoms usually include:
- Shakiness, sweating, or feeling cold and clammy
- Hunger, and a pounding or racing heartbeat
- Irritability, anxiety, or sudden mood change
- Difficulty concentrating, blurred vision, or slurred speech
- Tingling around the lips
Treat early symptoms promptly with fast-acting glucose as set out in your diabetes plan, then follow with longer-acting carbohydrate. See insulin and low blood sugar.
Other common effects:
- Weight gain, particularly when control improves after a period of high blood sugar. See insulin and weight gain.
- Redness, itching or swelling at injection sites
- Lumpy or thickened areas of fat where injections are repeated in the same spot, which makes absorption unpredictable. Rotating sites prevents this.
- Temporary blurred vision when blood sugar changes substantially
- Fluid retention and mild swelling when starting or intensifying treatment
Serious or persistent symptoms to discuss with a clinician
Severe hypoglycaemia is an emergency. Confusion, inability to swallow safely, seizures or loss of consciousness need emergency help. Do not give anything by mouth to someone who is not fully alert. If glucagon has been prescribed and someone with you knows how to give it, it should be used and emergency help still called.
Loss of hypo awareness. Over years, some people stop getting early warning symptoms and go straight to confusion. This is important to report, because it changes targets and monitoring.
Repeated hypos, particularly overnight or at a consistent time of day, mean the regimen needs adjusting rather than that you should simply eat more.
Allergic reaction. Widespread rash, swelling of the face or throat, or difficulty breathing needs emergency care. This is rare.
Also report persistent very high readings with thirst, frequent urination, vomiting or deep rapid breathing, which can indicate a different and equally urgent problem.
Dose changes, missed doses and monitoring tests
Insulin needs change with illness, activity, food, stress, weight and other medicines. Situations that commonly need a planned adjustment include unusual exercise, illness with vomiting, fasting, shift work and travel across time zones. Ask for rules covering each of these in advance.
There are different insulin types with different onset and duration, and mixing them up is a recognised cause of harm. Check the name and the pen every time, particularly after a repeat prescription.
Monitoring includes blood glucose and HbA1c, along with periodic checks of kidney function, eyes and feet as part of routine diabetes care. Injection sites should be examined regularly for thickened areas.
Interactions with OTC medicines and supplements
- Alcohol. Raises hypoglycaemia risk for hours afterwards, including overnight, and its effects can be mistaken for a hypo by onlookers.
- Beta blockers. Can mask the early warning symptoms of a hypo, particularly the racing heartbeat and shaking.
- Corticosteroids such as prednisone. Raise blood sugar and often need a temporary insulin increase. See prednisone side effects.
- Other diabetes medicines. Adding one may require an insulin reduction to avoid hypos.
- Supplements marketed for blood sugar. Unpredictable effects on top of a carefully titrated dose. See supplements with diabetes medication.
- Cough syrups and cold remedies. Some contain sugar; check with a pharmacist.
What to ask your doctor before changing treatment
- What exactly should I do when my blood sugar is low?
- What are my sick day rules if I am vomiting or cannot eat?
- How should I adjust around exercise, fasting or travel?
- Should someone at home have glucagon, and do they know how to use it?
- Can you check my injection sites and technique?
Related chronic medication guides
- Chronic medication side effects
- Managing chronic medication side effects
- Should I stop my chronic medication
- Over-the-counter medicines with chronic medication
- Report a side effect in South Africa
See also diabetes medication side effects and low blood sugar on diabetes medicine.
Medical Disclaimer: This content is for informational and educational purposes only and does not constitute medical diagnosis, prescription, or professional advice. Always read the patient information leaflet and consult a qualified doctor or pharmacist regarding any medicine or health concern.