If you are being treated for diabetes with insulin, you are already taking an important step toward maintaining your health. Insulin is a “friend” that helps your body control blood glucose effectively. However, this “friend” can sometimes cause minor inconveniences or even more serious problems that require special attention.

This article will help you understand the common side effects of insulin, how to recognize them, and, most importantly, when to seek immediate medical attention. These practical insights can help you feel more confident throughout your journey of living with diabetes.

Insulin injections: Side effects you should know and when to seek immediate medical attention

Are you currently receiving insulin therapy? Don't overlook important considerations regarding common side effects such as hypoglycemia and lipodystrophy, as well as appropriate medical management. This article provides detailed guidance to help patients use insulin safely and effectively and recognize warning signs that require immediate medical attention.

1. Common side effects of insulin

When using insulin, patients may experience certain side effects. There is no need to worry excessively, as many of these issues can be managed effectively.

1.1. Hypoglycemia (low blood glucose)

This is the most common side effect and requires particular attention [1, 2]. Hypoglycemia occurs when blood glucose falls below a safe level, typically below 3.9 mmol/L or 70 mg/dL [4]. Symptoms may include:

Intense hunger, trembling, and sweating.
Rapid heartbeat and palpitations.
Headache, dizziness, and drowsiness.
Feelings of anxiety, restlessness, or unusual irritability.
Blurred vision, slurred speech, or numbness and tingling in the lips, tongue, hands, or feet [3].

If not treated promptly, severe hypoglycemia can lead to confusion, seizures, coma, and other life-threatening complications [4].

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Signs of hypoglycemia

Initial management of mild to moderate hypoglycemia: (the patient is conscious and able to eat and drink) When mild symptoms of hypoglycemia occur, patients should take immediate action to prevent the condition from becoming more severe.

Step 1: Check blood glucose (if possible).
Step 2: Immediately consume 15 g of fast-acting carbohydrates. Choose one of the following:
- 1/2 can of regular soft drink (Note: Do not use diet or zero-sugar soft drinks).
- 1/2 cup of fruit juice (orange or apple).
- 1 tablespoon of sugar (or honey) diluted in water.
- 3–4 glucose tablets.
  Important note: Avoid eating chocolate, cream cakes, or drinking full-fat milk at this time because fat slows the absorption of sugar into the bloodstream.
Step 3: Rest and wait 15 minutes.
Step 4: Recheck blood glucose. If blood glucose remains low (below 3.9 mmol/L), repeat Steps 2 and 3.
Step 5: Once blood glucose has stabilized, have a snack or a main meal to help maintain stable blood glucose levels. If the condition does not improve after 2–3 treatment cycles, seek medical attention immediately at the nearest healthcare facility.

1.2. Weight gain

Some patients may notice weight gain after starting insulin injections [1, 2]. This is partly because insulin helps the body use glucose more effectively, and the body may sometimes store energy as fat. In addition, regularly eating extra food to manage episodes of hypoglycemia may also contribute to weight gain [2].

1.3. Injection-site reactions and lipodystrophy

If insulin is repeatedly injected into the same site or needles are reused multiple times, changes may develop in the skin and underlying tissue.

Injection-site reactions: After an insulin injection, patients may notice mild redness, swelling, itching, or pain at the injection site [1, 3]. These reactions are usually mild and resolve on their own.
Lipodystrophy:
- Skin thickening (lipohypertrophy): The skin at the injection site may become thicker, forming small lumps beneath the skin [1, 2].
- Skin depressions (lipoatrophy): Conversely, some patients may lose fatty tissue, resulting in depressions beneath the skin [2].

Injecting insulin into areas affected by lipodystrophy can cause unpredictable insulin absorption — sometimes resulting in insufficient absorption and high blood glucose, and at other times causing excessive insulin release and sudden hypoglycemia. This can be dangerous and make blood glucose control more difficult [2].

Important note: Needles should not be reused multiple times. Reused needles become dull and lose their lubricant coating, which can cause pain, bleeding, infection, and increase the risk of lipodystrophy.

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2. When should you seek immediate medical attention?

Although most side effects are mild, there are situations in which patients require urgent medical attention.

2.1. Signs of severe hypoglycemia

If you or a family member experiences signs of severe hypoglycemia, such as:

Loss of consciousness or inability to remain alert [3].
Seizures.
Inability to eat or drink or to take sugar orally to treat hypoglycemia [4].

This is a medical emergency. The patient should be taken to a healthcare facility immediately for prompt emergency treatment [3]. While waiting for medical assistance or on the way to the hospital, if the patient is unconscious, never attempt to force open the mouth or pour sugar water or any other liquid into the mouth, as this may cause aspiration into the lungs.

2.2. Signs of a severe allergic reaction

Systemic allergic reactions to insulin are very rare but can be life-threatening [3]. Seek immediate medical attention if the patient experiences any of the following:

Widespread severe rash or intense itching [3].
Swelling of the face, lips, tongue, or throat [3].
Difficulty breathing, wheezing, or chest tightness [3].
Severe dizziness, lightheadedness, or fainting [3].

2.3. Other persistent or worsening symptoms

If you experience any other side effects that concern you, or if your symptoms do not improve and instead become worse, do not hesitate to consult your doctor. It is important not to change your insulin dose on your own without medical advice.

3. Preventing and effectively managing insulin side effects

Patients can take proactive steps to minimize insulin-related side effects by:

Injecting the correct dose using the proper technique: Always carefully check the insulin dose before injection. Remember to rotate injection sites to prevent skin thickening or depressions and to promote consistent insulin absorption. A new injection site should be at least 1–2 cm (approximately one finger joint) away from the previous site. Avoid injecting too close to the navel or old scars. Make sure you use the injection technique you have been instructed to follow [3].
Storing insulin properly and paying attention to its temperature before injection: Insulin should be stored according to the manufacturer's instructions. To reduce injection discomfort, patients should warm the insulin pen in their hands before injection.
Monitoring blood glucose regularly: This helps patients better understand their body's response. Check blood glucose according to your doctor's schedule (before meals, before exercise, and before bedtime) [2]. This allows you to recognize signs of excessively high or low blood glucose early and take appropriate action.
Following a healthy diet and lifestyle: Eating regularly, maintaining consistent meal times, and balancing different nutrient groups can help stabilize blood glucose and reduce the risk of hypoglycemia [3]. Regular exercise is also beneficial, but consult your doctor or a nutritionist to adjust insulin doses and meals appropriately according to exercise intensity [2].
Always communicate with your doctor: Do not hesitate to share any concerns or questions about insulin side effects with your doctor or nurse. They can adjust the dosage or type of insulin or provide helpful advice to improve blood glucose management.

4. Frequently asked questions (FAQ)

How long will I need to use insulin? The duration of insulin therapy depends on the patient's diabetes condition. Some people only need insulin temporarily during certain periods (for example, during pregnancy or serious illness), while others, such as people with type 1 diabetes, will need insulin for life. Your doctor will provide specific advice based on your diagnosis and treatment goals.
What should I do if I miss an insulin dose? If you miss an insulin dose, it is important not to take a double dose on your own, as this can lead to dangerous hypoglycemia. The appropriate course of action may vary depending on the type of insulin and how long ago the dose was missed. It is best to discuss a “missed-dose plan” with your doctor so that you have specific and safe instructions for the insulin you are using.

5. Medical review and references

Medical consultation:

MSc, MD. Nguyen Dinh Tuan — Department of Endocrinology, University Medical Center Ho Chi Minh City

References:

[1] Thota, S., & Akbar, A. (2023). Insulin. StatPearls. Truy cập: 2025-12-02. URL: https://www.ncbi.nlm.nih.gov/books/NBK560688/
[2] Donnor, T., & Sarkar, S. (2023). Insulin- Pharmacology, Therapeutic Regimens and Principles of Intensive Insulin Therapy. Endotext. Truy cập: 2025-12-02. URL: https://www.ncbi.nlm.nih.gov/books/NBK278938/
[3] Mayo Clinic. (2025). Insulin lispro (intravenous route, subcutaneous route) - Side effects & dosage. Truy cập: 2025-12-02. URL: https://www.mayoclinic.org/drugs-supplements/insulin-lispro-intravenous-route-subcutaneous-route/description/drg-20064334
[4] Rubin, R., Khanna, N. R., & McIver, L. A. (2024). Aspart Insulin. StatPearls. Truy cập: 2025-12-02. URL: https://www.ncbi.nlm.nih.gov/books/NBK500030/

The information above is for reference purposes only and is not intended as medical advice. Please contact your doctor for detailed medical consultation.

Insulin Injections: Side effects and emergency signs

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