Tresiba Side Effects: What to Expect and When to Call Your Doctor

Tresiba (insulin degludec) is a widely used and generally well-tolerated basal insulin. However, like all insulins, it carries the risk of side effects — some manageable and expected, others serious and requiring immediate medical attention. Knowing what to watch for gives you confidence and helps you respond quickly when something isn't right.

The Most Common Side Effect: Low Blood Sugar (Hypoglycemia)

By far the most common and clinically significant side effect of Tresiba is hypoglycemia (low blood sugar). All insulins carry this risk because they lower blood sugar — sometimes too much. Tresiba's ultra-long, peakless profile actually provides a meaningful advantage here: clinical trials showed it reduces the risk of severe hypoglycemia by 40% compared to insulin glargine (Lantus) in type 2 diabetes patients. However, hypoglycemia can still occur.

Symptoms of hypoglycemia include:

Dizziness or lightheadedness

Sweating (especially cold sweats)

Shakiness or trembling

Confusion or difficulty concentrating

Irritability or mood changes

Rapid heartbeat (palpitations)

Hunger or nausea

Pale skin, headache, weakness

What to do: If you can, eat or drink a fast-acting source of sugar (4 oz fruit juice, 3-4 glucose tablets, regular soda). Check your blood sugar. If symptoms are severe or you lose consciousness, call 911 immediately.

Other Common Side Effects

Injection site reactions: Redness, swelling, itching, or minor bruising at the injection site. Usually mild and temporary. Rotating injection sites at each dose helps reduce this.

Weight gain: Insulin promotes energy storage, which can lead to weight gain over time. Eating a balanced diet and exercising regularly can help minimize this. Discuss with your doctor if weight gain is significant.

Edema (swelling): Swelling in hands and feet can occur, especially when starting insulin or changing doses. Usually mild and resolves on its own.

Lipodystrophy: Skin thickening or pitting at injection sites from repeated injections in the same spot. Rotating sites prevents this. If lipodystrophy develops, injecting into affected areas can cause unpredictable insulin absorption.

Upper respiratory symptoms: Cold symptoms and headache have been reported. These are typically mild.

Serious Side Effects: When to Seek Immediate Help

These are less common but require urgent medical attention:

Severe hypoglycemia: Seizures, loss of consciousness, or inability to swallow. Call 911 immediately. Someone nearby may need to administer glucagon if available.

Hypokalemia (low potassium): Tresiba can cause low potassium levels, which can be life-threatening. Symptoms include leg cramps, constipation, irregular heartbeat, increased thirst or urination, numbness or tingling, muscle weakness. Contact your doctor immediately if you experience these.

Severe allergic reactions (anaphylaxis): Signs include hives, severe itching, rash, difficulty breathing, fast heartbeat, sweating, extreme drowsiness, swelling of the face, lips, tongue, or throat. Stop Tresiba and call 911 immediately.

Heart failure (with TZDs): Taking Tresiba with thiazolidinedione (TZD) medications like pioglitazone (Actos) or rosiglitazone can cause or worsen heart failure. Contact your doctor if you experience new or worsening shortness of breath, sudden weight gain, or swelling in your ankles or feet.

Special Warning: Don't Share Your Tresiba Pen

Never share your Tresiba FlexTouch pen with another person, even if the needle has been changed. Sharing insulin pens can transmit serious blood-borne infections including HIV and hepatitis. Each pen is for one person only.

Reducing Your Risk of Side Effects

Monitor blood sugar regularly and as directed by your doctor

Rotate injection sites at every dose to prevent lipodystrophy

Avoid alcohol — it can unpredictably raise or lower blood sugar when combined with Tresiba

Tell your doctor about all medications you take — many drugs interact with insulin and can affect blood sugar levels

For a complete guide to drug interactions, see: Tresiba Drug Interactions: What to Avoid and What to Tell Your Doctor.

If you're having trouble finding Tresiba in stock, medfinder can help you locate it at pharmacies near you.