Novolog (insulin aspart) is a rapid-acting insulin analog used for mealtime blood sugar control in adults and children with type 1 or type 2 diabetes. It starts working in 5 to 15 minutes, peaks around 30 to 90 minutes, and lasts 3 to 5 hours. Novolog is given by injection 5 to 10 minutes before meals or used continuously in insulin pumps. Dose is individualized based on carbohydrate intake, pre-meal glucose, and prescriber guidance.
What Novolog Is
Novolog is the brand name for insulin aspart, manufactured by Novo Nordisk. It is a rapid-acting (sometimes called prandial or bolus) insulin analog designed to cover the surge in blood glucose that follows meals. Unlike basal insulins, which work slowly and steadily in the background, Novolog acts quickly and clears quickly — matching the timing of carbohydrate absorption from food.
It is FDA-approved for adults and children age 2 years and older with type 1 or type 2 diabetes. Novolog can be delivered by syringe and vial, FlexPen, PenFill cartridge, or in continuous subcutaneous insulin infusion via insulin pump.
How Novolog Works
Insulin aspart differs from human insulin by a single amino acid substitution — proline at position B28 is replaced by aspartic acid. This change reduces the tendency of insulin molecules to clump into hexamers (six-molecule clusters) and dimers at the injection site. Because absorption requires breakdown to single molecules, the reduced clumping means faster absorption into the bloodstream.
Once absorbed, insulin aspart binds to insulin receptors on liver, muscle, and fat cells with the same affinity as human insulin, suppressing liver glucose production and increasing glucose uptake by muscle and fat tissue.
Pharmacokinetics: Onset, Peak, Duration
| Parameter | Novolog (insulin aspart) |
|---|---|
| Onset of action | 5 to 15 minutes |
| Peak effect | 30 to 90 minutes |
| Duration of action | 3 to 5 hours |
| Recommended timing | 5 to 10 minutes before a meal |
| Concentration | U-100 (100 units/mL) |
| Half-life (subcutaneous) | Approximately 81 minutes |
Who Novolog Is For
- Adults with type 1 diabetes for prandial coverage as part of basal-bolus therapy
- Adults with type 2 diabetes who need mealtime insulin in addition to basal insulin or oral therapy
- Children age 2 years and older with diabetes
- People using insulin pumps (continuous subcutaneous insulin infusion)
- People hospitalized with hyperglycemia requiring scheduled mealtime insulin
How Novolog Is Used
Novolog is injected subcutaneously into the abdomen, thigh, upper arm, or buttocks. Site rotation reduces lipohypertrophy. Typical use patterns include:
- Inject 5 to 10 minutes before starting a meal
- Use carbohydrate counting plus correction for pre-meal glucose to determine each dose
- In insulin pumps, deliver as a continuous basal rate plus pre-meal boluses
- Pair with a long-acting basal insulin (Lantus, Toujeo, Tresiba, Levemir) for full type 1 coverage
Starting ratios are typically estimated by the prescriber from total daily insulin needs and refined by post-meal glucose monitoring or continuous glucose monitor data. Do not use another person’s ratios and do not self-titrate aggressively without prescriber input — the risk of hypoglycemia is real.
Novolog vs Other Rapid-Acting Insulins
| Insulin | Onset | Peak | Duration | Notes |
|---|---|---|---|---|
| Novolog (aspart) | 5 to 15 min | 30 to 90 min | 3 to 5 hr | Most widely used; pediatric label age 2+ |
| Humalog (lispro) | 5 to 15 min | 30 to 90 min | 3 to 5 hr | Similar profile and clinical effect |
| Apidra (glulisine) | 10 to 15 min | 60 to 90 min | 3 to 4 hr | Slightly shorter duration |
| Fiasp (faster aspart) | ~2 to 5 min | ~60 min | 3 to 5 hr | Same molecule plus niacinamide for faster absorption |
| Lyumjev (faster lispro) | ~1 to 3 min | ~60 min | 4 to 5 hr | Lispro with treprostinil and citrate |
| Humulin R / Novolin R (regular) | 30 min | 2 to 4 hr | 5 to 8 hr | Older human insulin; inject 30 minutes before meals |
Mealtime Dosing Concepts
Three numbers commonly guide a Novolog mealtime dose:
- Insulin-to-carbohydrate ratio (ICR): how many grams of carbohydrate are covered by 1 unit of insulin (commonly between 1:8 and 1:15)
- Correction factor (sensitivity factor): how many mg/dL one unit of insulin lowers blood glucose (commonly between 30 and 60 mg/dL per unit)
- Target blood glucose: the goal value before a meal, set by the prescriber
These three numbers are estimated initially and refined with experience. Carbohydrate counting accuracy is the single biggest variable affecting post-meal glucose, often more than dose precision itself.
Side Effects
- Hypoglycemia (low blood sugar) — most common side effect; can occur 1 to 4 hours after the dose
- Weight gain — common with intensified insulin therapy
- Injection site reactions — redness, itching, small bumps
- Lipodystrophy (lipohypertrophy or lipoatrophy) from repeated injections in the same spot
- Hypokalemia (low potassium) — uncommon but possible
- Allergic reactions — rash, itching, rare anaphylaxis
- Peripheral edema, especially with thiazolidinediones
Combination Products and Biosimilars
- Novolog Mix 70/30: 70 percent protaminated aspart (intermediate) plus 30 percent aspart (rapid) for twice-daily premix dosing
- Ryzodeg 70/30: 70 percent degludec (ultra-long basal) plus 30 percent aspart (rapid) for once- or twice-daily dosing
- Insulin aspart-szjj (Merilog): FDA-approved biosimilar to Novolog, providing a lower-cost equivalent
- Fiasp: faster-acting version of insulin aspart with niacinamide added to speed absorption
Cost and Access
- Brand Novolog typically costs about $300 to $500 per month at retail without insurance for usual mealtime use
- Novo Nordisk’s My$99Insulin and Insulin Patient Assistance Program cap Novolog at $35 per month for eligible patients
- Medicare Part D and Medicaid cover Novolog at $35 per month under federal price provisions
- The Merilog biosimilar offers a lower-cost alternative
- Most commercial plans cover Novolog, often as the preferred rapid analog
Storage and Handling
- Unopened pens and vials: refrigerate at 36 to 46 °F (2 to 8 °C)
- In use: room temperature up to 86 °F (30 °C) for up to 28 days (vials and pens), then discard
- Insulin pump reservoir: change every 6 days at most
- Do not freeze; do not expose to direct sunlight
- Solution is clear — discard if cloudy or discolored
Related Reading
For more, see our overview of diabetes treatment, the comparison guide on Novolog Mix 70/30, and carb counting for insulin.
The Bottom Line
Novolog (insulin aspart) is a rapid-acting mealtime insulin used in type 1 and type 2 diabetes, with onset in 5 to 15 minutes, peak at 30 to 90 minutes, and duration of 3 to 5 hours. It is delivered by pen, syringe, or insulin pump and is paired with a basal insulin for full coverage. Dose is calculated from carbohydrate counting and correction factors that the prescriber individualizes. Side effects include hypoglycemia, weight gain, and injection site reactions. A biosimilar (Merilog) and a Novo Nordisk $35 cap program reduce out-of-pocket cost. Talk to your diabetes team to set up appropriate ratios, technique, and post-meal monitoring before starting or adjusting.
