Short answer: Low blood sugar (hypoglycemia) is the most common NovoLog side effect, as with all insulin. Severe low blood sugar affected 17% of adults and 6% of children with type 1 diabetes over 24 weeks, and 10% of adults with type 2. In the type 1 trial, headache affected 12% and accidental injury 11%. In type 2, hyporeflexia affected 11%. NovoLog has no boxed warning.
What NovoLog is approved for: NovoLog is a rapid-acting mealtime insulin approved to improve blood sugar control in adults and children with diabetes (section 1).
Source
NOVOLOG (insulin aspart) injection, for subcutaneous or intravenous use, prescribing information and Patient Information. Novo Nordisk. DailyMed, version published January 22, 2025. DailyMed setid 3a1e73a2-3009-40d0-876c-b4cb2be56fc5
No. The current NovoLog label has no boxed warning.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on NovoLog.
| Adverse reaction | NOVOLOG + NPH, % (n=596) | Regular Human Insulin + NPH, % (n=286) |
|---|---|---|
| Headache | 12 | 10 |
| Injury accidental | 11 | 10 |
| Nausea | 7 | 5 |
| Diarrhea | 5 | 3 |
Excluding low blood sugar. Both arms also took NPH insulin; the comparison is regular human insulin, not placebo. Mean exposure was 24 weeks.
| Adverse reaction | NOVOLOG + NPH, % (n=91) | Human Regular Insulin + NPH, % (n=91) |
|---|---|---|
| Hyporeflexia | 11 | 7 |
| Onychomycosis | 10 | 5 |
| Sensory disturbance | 9 | 7 |
| Urinary tract infection | 8 | 7 |
| Chest pain | 5 | 3 |
| Headache | 5 | 3 |
| Skin disorder | 5 | 2 |
| Abdominal pain | 5 | 1 |
| Sinusitis | 5 | 1 |
Mean exposure was 24 weeks.
| Group | Severe hypoglycemia |
|---|---|
| Type 1 adults, injections, 24 weeks | 17% |
| Type 1 children, injections, 24 weeks | 6% |
| Type 2 adults, injections, 24 weeks | 10% |
| Type 1 adults, insulin pump, 16 weeks | 2% |
| Type 1 children, insulin pump, 16 weeks | 10% |
| Type 2 adults, insulin pump, 16 weeks | None reported |
Severe meant low blood sugar with nervous system symptoms needing another person's help or a hospital stay. The label warns that comparing these rates with other products may be misleading.
Redness, local swelling and itching at the injection site have occurred and were usually self-limiting. Severe whole-body allergy (anaphylaxis) has been reported.
Fast improvement in blood sugar control has been linked to a temporary change in eye focus, worsening diabetic eye disease and painful nerve symptoms. Skin pits or thickening, swelling from sodium retention and weight gain can also occur.
In a 6-month study with a 6-month extension in type 1 adults, 99.8% on NovoLog tested positive for anti-insulin antibodies at least once (97.2% already at baseline), and 92.1% for anti-drug antibodies (64.6% at baseline). The label says these antibodies did not worsen control or require more insulin.
Reported after approval: other insulins given by mistake in place of NovoLog, and localized cutaneous amyloidosis (lumps under the skin) at injection sites. Injecting into those lumps has raised blood sugar, and a sudden switch to normal skin has lowered it.
The Patient Information lists other common side effects as low potassium, injection site reactions, itching, rash, serious allergic reactions, skin pits or thickening, weight gain and swelling of the hands and feet.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Who should not use it. NovoLog is not used during an episode of low blood sugar, or by people allergic to NovoLog or one of its inactive ingredients.
Never share a pen or cartridge. FlexPen, FlexTouch, PenFill cartridges and cartridge devices are never shared, even if the needle is changed, and vial users never share needles or syringes, because of the risk of passing on blood-borne infections.
Changes in insulin regimen. Changing insulin strength, maker, type, injection site or method can cause high or low blood sugar, so changes are made under close medical supervision with more glucose checks. In type 2 diabetes, other diabetes medicines may need adjusting.
Low blood sugar. Hypoglycemia is the most common reaction to all insulins. Severe episodes can cause seizures, unconsciousness or death and can affect driving. Awareness of lows may be reduced with long diabetes, nerve damage, beta-blockers or repeated lows. Kidney or liver problems can raise the risk.
Medication mix-ups. Mix-ups between insulin products have been reported, so the insulin label is checked before each injection.
Serious allergic reactions. Severe, life-threatening whole-body allergy, including anaphylaxis, can occur; NovoLog is stopped if it does.
Low potassium. All insulins can shift potassium into cells and cause low potassium, which untreated can cause breathing paralysis, heart rhythm problems and death.
Heart failure with TZDs. Thiazolidinediones (such as pioglitazone) with insulin can cause fluid retention that may lead to or worsen heart failure.
Insulin pump failure. A pump or infusion set malfunction, or degraded insulin, can quickly lead to high blood sugar and ketoacidosis. Pump users are trained to give insulin by injection and keep backup insulin on hand.
From the Patient Information that comes with NovoLog:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.