What insulin does and why you might need it

Insulin is a hormone your pancreas makes to move glucose (blood sugar) from your bloodstream into your cells, where it gets used for energy. When you have diabetes, your pancreas either makes little or no insulin, or your body cannot use the insulin it makes. Without enough working insulin, glucose builds up in your blood and causes damage over time.

Not everyone with diabetes needs insulin. People with type 2 diabetes often manage blood sugar with oral medications, diet, and exercise first. But if those do not work well enough, or if you have type 1 diabetes, insulin becomes necessary. Your doctor will test your blood sugar levels and discuss whether insulin is the right next step for you.

Key Takeaways

  • Insulin comes in four main types — rapid-acting, short-acting, intermediate-acting, and long-acting — and your doctor chooses based on how quickly you need it to work and how long you need it to last.
  • You inject insulin under the skin using a syringe, pen, or pump; it cannot be taken by mouth because stomach acid destroys it.
  • The cost of insulin varies widely by brand, type, and whether your insurance covers it, but patient information programs and state programs can reduce what you pay out of pocket.
  • Most people on insulin need to check their blood sugar several times a day and keep a log to share with their doctor so doses can be adjusted.
  • Hypoglycemia (low blood sugar) is the most common side effect of insulin, and you should always carry fast-acting carbohydrates and know the signs.

The four main types of insulin and how they work

Insulin is grouped by how fast it starts working and how long it lasts in your body. Rapid-acting insulin (like Humalog, NovoLog, and Apidra) begins working in 10 to 15 minutes and peaks in 1 to 2 hours. You take it right before or during meals to cover the carbohydrates you eat. Short-acting or regular insulin (like Humulin R and Novolin R) takes 30 minutes to start and peaks in 2 to 4 hours — it is older and less commonly used now, but still available and often cheaper.

Intermediate-acting insulin (NPH, sold as Humulin N and Novolin N) starts working in 1 to 2 hours and peaks in 4 to 12 hours. It is often mixed with rapid-acting insulin to cover both meals and background blood sugar. Long-acting insulin (like Lantus, Levemir, and Toujeo) works slowly and steadily for 24 hours or longer, providing a steady baseline of insulin throughout the day and night.

Most people on insulin use a combination: a long-acting insulin once or twice daily for background coverage, plus rapid-acting insulin at meals. Your doctor will choose the mix based on your blood sugar patterns, how many meals you eat, and your daily routine. The goal is to keep your blood sugar in a target range most of the time.

How to inject insulin and what devices are available

Insulin must be injected under the skin because it is a protein and would be broken down by stomach acid if swallowed. You have three main options for delivery: a syringe and vial, a prefilled pen, or an insulin pump.

Syringes and vials are the least expensive option. You draw the insulin from a vial into a syringe and inject it into your abdomen, thigh, arm, or buttock. You need to rotate injection sites to avoid lipohypertrophy (thickened skin that can make insulin absorb unevenly). Syringes come in different sizes depending on how much insulin you need per injection.

Insulin pens look like thick markers and hold a cartridge of insulin. You dial the dose, attach a needle, and inject. Pens are easier to carry and more convenient than syringes, but they cost more. Some pens are prefilled and disposable; others are reusable and you swap out cartridges.

Insulin pumps are small devices worn on your body (usually clipped to your belt or in a pocket) that deliver insulin through a thin tube under your skin. The pump releases small amounts of long-acting insulin continuously and larger amounts when you tell it to (at meals). Pumps give the most precise control but are the most expensive and require more training to use safely.

Understanding insulin costs and finding financial help

Insulin prices vary widely depending on the brand, type, and your insurance. A vial of insulin can cost anywhere from $25 to over $300 without insurance or information, and many people need multiple vials per month. Even with insurance, copays can be $35 to $100 per prescription.

If cost is a barrier, several routes can lower what you pay. Most insulin manufacturers offer patient information programs that provide insulin free or at reduced cost if your income is below a certain threshold. You can find these programs on the manufacturer's website or ask your doctor's office to help you find one. Some programs require you to reapply each year.

Many states have programs that help uninsured or underinsured people pay for insulin. A few states have capped the copay at $35 per month for a 30-day supply. Your state health department website or a local diabetes educator can tell you what programs exist where you live. The 211 helpline (dial 2-1-1 or visit 211.org) can also connect you to local resources.

If you have Medicare, insulin is covered under Part D (prescription drug coverage). If you have Medicaid, coverage varies by state. If you have private insurance, check your plan documents to see what insulin is covered and what your copay will be.

Monitoring your blood sugar and adjusting your dose

Once you start insulin, you will need to check your blood sugar regularly — usually before meals and at bedtime, and sometimes two hours after meals. You use a glucose meter (a small device that reads a drop of blood from a finger prick) to get a number. Most people on insulin keep a log of these numbers to show their doctor at appointments.

Your doctor will use your blood sugar log to decide whether your insulin dose is right. If your blood sugar is too high most of the time, your dose may need to go up. If it is too low, your dose may need to go down. Some people adjust their own doses based on what they eat and their activity level — this is called carbohydrate counting — but you should only do this after your doctor trains you.

Continuous glucose monitors (CGMs) are devices that measure your blood sugar every few minutes and send the reading to a receiver or your phone. They reduce the number of finger pricks you need and give you a clearer picture of how your blood sugar changes throughout the day. Many insurance plans cover CGMs, though copays vary. Ask your doctor whether a CGM might help you.

Low blood sugar (hypoglycemia) and what to do

The most common side effect of insulin is hypoglycemia — blood sugar that drops too low, usually below 70 mg/dL. This can happen if you take too much insulin, skip a meal, exercise more than usual, or drink alcohol without eating. Symptoms include shakiness, sweating, rapid heartbeat, anxiety, hunger, tingling lips, and confusion. Severe hypoglycemia can cause seizures or loss of consciousness.

If you feel hypoglycemic symptoms, check your blood sugar if you can. If it is low, eat or drink 15 grams of fast-acting carbohydrates — a half cup of juice, three glucose tablets, a tablespoon of honey, or five hard candies. Wait 15 minutes and check again. If it is still low, repeat. Once your blood sugar is above 100 mg/dL, eat a snack with protein and fat (like peanut butter and crackers) to keep it stable.

Always carry fast-acting carbohydrates with you. Tell family, friends, and coworkers about your diabetes and where you keep your carbohydrates. If you lose consciousness, someone may need to give you a glucagon injection — a hormone that raises blood sugar quickly. Ask your doctor for a glucagon kit and make sure the people around you know how to use it.

Storage, travel, and day-to-day management

Insulin is sensitive to temperature. Unopened vials and pens should be stored in the refrigerator at 36°F to 46°F. Once you open a vial or pen, you can keep it at room temperature (below 86°F) for 28 days — check the package insert for your specific insulin because timing varies. Never freeze insulin or leave it in direct sunlight. If insulin has been frozen or overheated, throw it away and use a new vial.

If you travel, bring extra insulin in your carry-on bag (not checked luggage, where it can freeze or overheat). Bring your syringes, pens, or pump supplies as well. If you cross time zones, talk to your doctor before you leave about how to adjust your insulin schedule. Bring a letter from your doctor stating that you have diabetes and need to carry syringes and insulin — this can help if you are stopped at airport security.

Keep a list of your insulin type, dose, and injection times. Share this with your doctor, pharmacist, and anyone who might need to help you in an emergency. If you miss a dose, do not double up the next time — just take your next dose as scheduled and tell your doctor at your next visit.

Frequently Asked Questions

Can I switch insulin brands if my insurance stops covering mine?

Sometimes, but not always safely on your own. Different insulin brands work slightly differently and may require dose adjustments. Always talk to your doctor before switching. They can help you find a covered insulin that will work for you, or they can request a prior authorization from your insurance to cover your current insulin.

What happens if I cannot afford my insulin?

Contact your insulin manufacturer's patient information program first — most offer free or low-cost insulin based on income. Call your state health department to ask about state insulin programs. Your doctor's office may also have samples or know of local clinics that provide insulin at reduced cost. Do not skip doses to make insulin last longer; this is dangerous and usually makes your blood sugar worse.

Do I need to take insulin forever?

If you have type 1 diabetes, yes — your pancreas cannot make insulin, so you will need it for life. If you have type 2 diabetes, it depends. Some people can reduce or stop insulin if they lose weight, exercise regularly, and manage their diet very well. Others will need it long-term. Your doctor will reassess at each visit.

Can I use an insulin pump if I have type 2 diabetes?

Yes. Pumps are used by people with both type 1 and type 2 diabetes. Your doctor will recommend a pump if you need insulin and would benefit from more precise dosing or more flexibility in your daily routine. Insurance coverage varies, so check your plan.

What should I do if I accidentally inject insulin twice?

Call your doctor or poison control right away. Do not wait to see if symptoms develop. You may need to eat extra carbohydrates or go to an urgent care to be monitored. Keep the phone number for poison control (1-800-222-1222) posted somewhere visible.