Insulin pumps use rapid-acting insulin. The three most common are insulin lispro (Humalog), insulin aspart (NovoLog), and insulin glulisine (Apidra), all of which start working within 5 to 15 minutes, peak between 30 and 90 minutes, and wear off in under 5 hours. Unlike injection-based regimens that pair a rapid insulin with a separate long-acting one, a pump replaces both by delivering tiny, continuous pulses of the same rapid-acting insulin around the clock.
Why Pumps Only Need One Type of Insulin
If you take insulin by pen or syringe, you typically need two kinds: a long-acting insulin that covers your baseline needs for 12 to 24 hours, and a rapid-acting insulin you inject before meals. A pump eliminates that split. It delivers rapid-acting insulin in two distinct modes, both from a single reservoir.
The first mode is basal delivery: a slow, steady drip that trickles insulin into the tissue beneath your skin day and night. Pumps can deliver basal insulin in increments as small as 0.01 units per hour, and you can program different rates for different times of day. This mimics the low-level insulin your pancreas would normally release between meals and overnight. The second mode is bolus delivery: a larger dose you trigger before eating or to correct a high reading. Bolus increments can be as small as 0.025 units, which is more precise than any pen or syringe can achieve.
Because rapid-acting insulin kicks in within minutes and clears the body in a few hours, the pump can adjust on a short timeline. If you need more insulin overnight and less in the afternoon, the pump simply speeds up or slows down its micro-pulses. Long-acting insulin can’t do this because its slow absorption profile is baked in at the time of injection.
The Three Standard Rapid-Acting Insulins
All three rapid-acting insulin analogues approved for pump use share nearly identical timing profiles:
- Insulin lispro (Humalog), made by Lilly. Onset in 5 to 15 minutes, peak at 30 to 90 minutes, effective duration under 5 hours.
- Insulin aspart (NovoLog), made by Novo Nordisk. Same onset, peak, and duration window.
- Insulin glulisine (Apidra), made by Sanofi. Same onset, peak, and duration window.
In practice, many people find that one brand works slightly better for them in terms of absorption consistency or site reactions, but the clinical differences between the three are small. Your endocrinologist or diabetes team will often base the choice on insurance coverage, availability, and personal experience.
Ultra-Rapid Insulins: Fiasp and Lyumjev
A newer generation of insulins has been designed to absorb even faster. Fiasp is a reformulation of insulin aspart with added ingredients that speed absorption, giving it an onset roughly 5 minutes faster than standard aspart. Lyumjev does the same for insulin lispro, with an onset about 11 minutes faster than standard lispro.
These ultra-rapid options are increasingly used in pumps, particularly in automated insulin delivery (AID) systems that pair a pump with a continuous glucose monitor. The faster the insulin starts working, the better these closed-loop systems can respond to rising blood sugar after meals. Research using ultra-rapid insulins in hybrid closed-loop setups has shown they can help tighten glucose control around mealtimes, though individual results vary. Not every pump manufacturer has formally approved ultra-rapid formulations for use in their devices, so it’s worth checking compatibility with your specific system.
Can Regular Insulin Be Used in a Pump?
Technically, yes. Regular human insulin (sometimes called “R” insulin) was used in early insulin pumps before rapid-acting analogues became available. It has a slower onset of about 30 minutes and lasts longer than the rapid-acting options. Some people still use it, often for cost reasons, since regular insulin is generally cheaper. However, its slower action makes it harder for the pump to fine-tune blood sugar in real time, and it’s not compatible with automated delivery algorithms that assume rapid-acting timing. For this reason, clinical guidelines and pump manufacturers strongly favor rapid-acting analogues.
Higher Concentrations for Higher Doses
Standard insulin for pumps comes in a concentration of U-100, meaning 100 units per milliliter. Most pump reservoirs hold between 1.6 and 3.0 milliliters, which provides 160 to 300 units of U-100 insulin. For many people, that lasts the recommended 2 to 3 days before the reservoir and infusion set need to be changed.
But if your daily insulin needs are high, that reservoir can run out fast. People who need more than about 50 units per day with a smaller cartridge, or more than 95 units per day with a larger one, may find themselves swapping reservoirs more often than every 72 hours. In those cases, U-200 insulin (200 units per milliliter) effectively doubles the supply in the same physical space. Recent clinical experience with U-200 lispro in automated delivery systems like the Omnipod 5, Tandem Control-IQ, and Medtronic 780G has shown it can work well for adolescents and adults with higher requirements.
U-200 isn’t appropriate for everyone. People with smaller daily insulin needs should avoid it because pumps are less accurate when delivering the very tiny volumes that a concentrated insulin would require for small doses. U-500 regular insulin also exists but has a much longer action profile of 18 to 21 hours, making it incompatible with the rapid-adjustment logic that automated pump systems rely on.
Keeping Insulin Stable Inside the Pump
Insulin sitting in a pump reservoir is exposed to body heat and movement all day, which gradually breaks it down. The FDA recommends discarding insulin in a pump’s infusion set (the reservoir, tubing, and catheter) after 48 hours. If the pump is exposed to temperatures above 98.6°F, such as during intense exercise, a hot bath, or a summer day at the beach, the insulin should be replaced immediately.
In real-world use, reservoir temperatures tend to hover around 86°F (30°C) across all seasons, which is lower than the worst-case conditions used in lab stability testing. That’s reassuring, but it doesn’t mean you can stretch reservoir changes much beyond the 48- to 72-hour window most manufacturers recommend. Degraded insulin won’t look different in the reservoir, but you may notice unexplained high blood sugar readings as a sign that the insulin has lost potency.
Storing unopened insulin vials or pens in the refrigerator and only warming the current vial to room temperature is the simplest way to ensure what goes into your pump is at full strength.