Understanding Toujeo Side Effects

Starting a new medication can feel uncertain, especially when it involves daily injections. If you've been prescribed Toujeo (Insulin Glargine U-300), knowing what side effects to expect — and which ones need medical attention — can help you feel more confident about your treatment.

This guide covers the common and serious side effects of Toujeo based on FDA labeling, who may be more at risk, and practical tips for managing them.

What Is Toujeo?

Toujeo is a long-acting basal insulin made by Sanofi. It contains insulin glargine at a concentration of 300 units per mL (U-300), which is three times more concentrated than standard Lantus (U-100). This higher concentration creates a smaller depot under the skin, resulting in a flatter, more prolonged insulin release over approximately 24 to 36 hours.

Toujeo is approved for adults with type 1 and type 2 diabetes. For a full overview, see our guide on what Toujeo is and how it's used.

Common Side Effects of Toujeo

Most people taking Toujeo tolerate it well, but some side effects are relatively common. These are usually mild and may improve as your body adjusts:

• Hypoglycemia (low blood sugar) — This is the most common side effect of any insulin. Symptoms include shakiness, sweating, fast heartbeat, dizziness, hunger, confusion, and irritability. Toujeo's flatter profile may reduce the risk of hypoglycemia compared to Lantus, but it can still occur.
• Injection site reactions — Redness, swelling, itching, or mild pain at the injection site. Rotating your injection sites (abdomen, thigh, upper arm) helps reduce this.
• Weight gain — Insulin therapy commonly leads to some weight gain. This is because insulin helps your body use glucose more effectively, and some of that glucose gets stored as fat.
• Edema (swelling) — Mild swelling in the hands, ankles, or feet can occur, especially when starting insulin therapy.
• Lipodystrophy — Lumps or indentations at injection sites caused by repeated injections in the same spot. Rotating injection sites helps prevent this.
• Upper respiratory tract infections — Some patients report cold-like symptoms, including a runny nose (nasopharyngitis).

Serious Side Effects

While rare, some side effects of Toujeo require immediate medical attention:

• Severe hypoglycemia — Blood sugar that drops dangerously low can cause seizures, loss of consciousness, or even be life-threatening. If you can't treat a low blood sugar episode yourself, someone nearby should give you glucagon or call 911. Severe lows are more likely if you skip meals, exercise more than usual, drink alcohol, or take too much insulin.
• Hypokalemia (low potassium) — Insulin can shift potassium into cells, lowering blood potassium levels. Symptoms include muscle cramps, weakness, and irregular heartbeat. This is more of a concern if you're also taking medications that lower potassium, such as diuretics.
• Severe allergic reactions — Anaphylaxis is rare but possible. Signs include a whole-body rash, trouble breathing, rapid heartbeat, and swelling of the face or throat. Seek emergency care immediately if this happens.
• Heart failure — When Toujeo is used together with thiazolidinediones (TZDs) like Pioglitazone (Actos), the combination can increase the risk of heart failure and fluid retention. Tell your doctor if you experience sudden weight gain, shortness of breath, or swelling in your legs.

Specific Populations at Higher Risk

Some groups need extra caution when using Toujeo:

Older Adults

Elderly patients may be more sensitive to insulin and more prone to hypoglycemia. Doctors often start with lower doses and increase more gradually. Symptoms of low blood sugar may also be harder to recognize in older adults.

People with Kidney or Liver Problems

Your kidneys and liver help clear insulin from your body. If either organ isn't working well, insulin stays active longer, increasing the risk of hypoglycemia. Your doctor may need to adjust your Toujeo dose and monitor you more closely.

Pregnant or Breastfeeding Women

There isn't enough data on Toujeo specifically during pregnancy. Your doctor will weigh the benefits against the risks. If you're pregnant or planning to become pregnant, talk to your provider about whether Toujeo is the right insulin for you.

Children

Toujeo is not approved for use in children. Insulin Glargine U-100 products (like Lantus or Basaglar) are used in pediatric patients instead.

How to Manage Common Side Effects

Here are practical strategies for handling the most frequent Toujeo side effects:

Managing Hypoglycemia

• Always carry a fast-acting glucose source — glucose tablets, juice, or regular soda.
• Follow the "15-15 rule": eat 15 grams of fast-acting carbs, wait 15 minutes, and recheck your blood sugar.
• Don't skip meals. Eat consistent meals and snacks, especially after taking your insulin.
• Tell family members and coworkers how to recognize and treat low blood sugar.
• Consider wearing a medical ID bracelet.

Managing Injection Site Reactions

• Rotate injection sites within the same body region (e.g., different spots on your abdomen).
• Let the insulin reach room temperature before injecting — cold insulin stings more.
• Use a new needle for each injection.

Managing Weight Gain

• Work with your doctor or a dietitian on a meal plan that accounts for insulin therapy.
• Regular physical activity helps control blood sugar and manage weight.
• Don't reduce your insulin dose on your own to avoid weight gain — this can be dangerous.

When to Call Your Doctor

Contact your healthcare provider if you experience:

• Frequent low blood sugar episodes (more than 2-3 per week)
• Blood sugar that stays high despite taking Toujeo as prescribed
• Signs of an allergic reaction (rash, swelling, trouble breathing)
• Sudden weight gain, swelling, or shortness of breath
• Severe injection site reactions that don't improve
• Muscle cramps or weakness (possible hypokalemia)

If you experience severe hypoglycemia, a seizure, loss of consciousness, or signs of anaphylaxis, call 911 or go to the emergency room immediately.

Final Thoughts

Most people using Toujeo experience only mild side effects, with low blood sugar being the most common concern. Toujeo's U-300 formulation was specifically designed to provide a smoother insulin release, which may reduce hypoglycemia risk compared to some other long-acting insulins.

The key is knowing what to watch for and having a plan. Talk to your doctor about your individual risk factors, keep glucose tablets on hand, and don't hesitate to reach out to your healthcare team with questions.

If you're having trouble finding Toujeo at your pharmacy, Medfinder can help you locate pharmacies with Toujeo in stock near you.