70/30 insulin is a premixed insulin that combines two types of insulin in a single vial or pen: 70% intermediate-acting insulin and 30% fast-acting insulin. The intermediate portion controls blood sugar between meals and overnight, while the fast-acting portion handles the spike that comes after eating. It’s one of the most widely used insulin formulations for type 2 diabetes worldwide, designed to simplify treatment by covering two needs with one injection.
What’s Inside the Mix
The “70/30” refers to a specific ratio. In the human insulin version (sold as Novolin 70/30 or Humulin 70/30), that’s 70% NPH insulin, which is an intermediate-acting insulin, and 30% regular human insulin, which is short-acting. Both are structurally identical to the insulin your pancreas makes naturally.
There’s also an analog version, sometimes called NovoLog Mix 70/30 or Humalog Mix 75/25. These use newer, lab-modified insulins instead of the traditional human forms. The key difference: the fast-acting component in analog mixes works faster than regular insulin, kicking in within minutes rather than 30 to 60 minutes. This means the analog versions can be injected closer to mealtime, typically 5 to 10 minutes before eating, while the human insulin version needs about 15 to 30 minutes of lead time before a meal.
How It Works in Your Body
After you inject 70/30 insulin, two things happen on two different timelines. The short-acting component begins lowering blood sugar within 30 minutes to an hour. It peaks relatively quickly and handles the glucose surge from whatever you just ate. Meanwhile, the intermediate-acting component releases slowly, peaking somewhere between 2 and 12 hours after injection, and continues working for a total of 10 to 16 hours.
That wide peak window is important to understand. Unlike a single-type insulin with a narrow, predictable peak, 70/30 has a broad activity curve. Your blood sugar control depends partly on eating meals that roughly match the timing of those peaks. Skipping a meal or eating much later than planned after injecting can cause blood sugar to drop too low.
Who It Works Best For
70/30 insulin fits a specific kind of daily routine. It works best for people who eat meals of fairly consistent size and composition at regular times. If you tend to eat two or three similar-sized meals each day on a predictable schedule, this formulation can cover both your fasting and post-meal blood sugar with just one or two injections a day.
It’s also a practical choice for people who find more complex insulin regimens difficult to manage. A basal-bolus regimen, where you take a long-acting insulin plus a separate fast-acting injection at every meal, can mean four or more injections daily along with more frequent blood sugar monitoring. Premixed 70/30 reduces that burden. For people who are unwilling or unable to handle the demands of a multi-injection schedule, 70/30 offers a simpler alternative that still addresses both fasting and post-meal glucose levels.
Doctors typically start it once or twice daily, often timed with breakfast and dinner. Someone who has one particularly large meal per day might take it once daily before that meal, while someone with two substantial meals might inject twice.
Hypoglycemia Risk
Low blood sugar is the main safety concern with any insulin, and 70/30 carries a moderately higher risk of mild hypoglycemia compared to long-acting insulin alone. In clinical comparisons, people using premixed insulin analogs experienced roughly 0.28 to 0.34 more minor low blood sugar episodes per month than those on basal insulin only. Severe hypoglycemia, however, was rare and similar between both approaches.
The newer analog versions of 70/30 appear to cause fewer hypoglycemic episodes than the older human insulin versions. One pooled analysis found that premixed analogs reduced major hypoglycemic events by about 55% compared to premixed human insulin.
Nighttime lows deserve attention. Because the intermediate-acting component keeps working for up to 16 hours, an evening dose can still be active while you sleep. Eating a consistent dinner and monitoring blood sugar before bed helps reduce that risk.
Injection Timing and Meal Planning
When you inject relative to your meal matters. For the human insulin version (Novolin or Humulin 70/30), injecting 30 minutes before eating gives the regular insulin time to start working before food hits your bloodstream. Injecting too close to mealtime can mean your blood sugar spikes before the insulin catches up. Injecting too early without eating can cause a dangerous drop.
For the analog versions, the window is shorter. Studies on biphasic insulin aspart (the analog 70/30) found that injecting 5 minutes before a meal produced similar blood sugar control to injecting 15 to 20 minutes after, though post-meal spikes were slightly higher with the delayed injection. The practical takeaway: analog 70/30 gives you more flexibility around meals, but injecting a few minutes before eating is still ideal.
Mixing Before Each Injection
Unlike clear insulins that are ready to inject, 70/30 is a suspension, meaning it looks cloudy. The intermediate-acting insulin settles to the bottom over time, so you need to resuspend it before every injection. If you skip this step, you could inject an inconsistent dose, getting too much of one component and not enough of the other.
For a pen, the manufacturer recommends rolling it between your palms 10 times, then gently tipping it upside down and back 10 times until the liquid looks evenly milky. For a vial, the same rolling and inverting technique applies. Don’t shake it vigorously, which can create air bubbles and damage the insulin protein.
Storage and Shelf Life
Unopened 70/30 insulin should be stored in the refrigerator. Once you start using a vial or pen, it can stay at room temperature (between 59°F and 86°F) for up to 28 days. After that, discard it even if there’s insulin left. Extreme heat or cold damages insulin, so avoid leaving it in a car, near a window, or in the freezer. If the insulin looks clumpy, discolored, or has particles floating in it after mixing, don’t use it.
How 70/30 Compares to Other Regimens
The trade-off with 70/30 is flexibility versus simplicity. A basal-bolus regimen lets you adjust your mealtime dose based on what you’re eating, which gives tighter control. With 70/30, the ratio is fixed. You can’t take more fast-acting insulin for a bigger meal without also getting more intermediate-acting insulin. This makes it less adaptable for people with irregular eating habits or widely varying meal sizes.
On the other hand, when researchers compared premixed analog insulin to full basal-bolus therapy, there was no significant difference in hypoglycemia rates or weight gain between the two approaches. For many people with type 2 diabetes, the simpler regimen achieves comparable results with fewer daily injections and less complexity.
70/30 insulin is also one of the more affordable options. The human insulin versions (Novolin and Humulin 70/30) are available over the counter in many U.S. states and are significantly cheaper than analog formulations, making them a common choice when cost is a barrier to treatment.