Diabetes and Insulin Use: Dos and Don’ts
DiabetesType 1 Diabetes

Insulin Dos and Don’ts

Insulin Dos and Don’ts
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Updated on November 19, 2025
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If you’re on insulin to treat type 1 or type 2 diabetes, it’s critical to know exactly how to use it.

“Insulin can be a very dangerous drug if used improperly,” says Stanley Mathew, MD, an endocrinologist at Barnes-Jewish St. Peters Hospital in St. Peters, Missouri. “Correct dosing and correct technique of insulin administration are both crucial to prevent very high or very low blood sugar, both of which can have serious implications for one’s health.”

Do Take Mealtime Insulin Before You Start Eating

Short- or rapid-acting insulin is taken around mealtime to control the blood sugar rise that results from eating carbohydrates.

 If you use this type of insulin, do so 15 minutes before mealtime, says Rachel Halverson, CDCES, RN, a board-certified diabetes care and education specialist and the founder of Give Me Some Sugar in Acworth, Georgia. “This insulin takes some time to start working, so taking it before your meal gives it a head start.”

This protocol essentially mimics what the body does naturally, since the pancreas typically releases some insulin when you’re even thinking about food, she says.

If it’s challenging for you to get into this habit, Halverson recommends pairing it with another daily habit. “Take your insulin when making coffee or brushing your teeth,” she says. And if your provider recommends taking insulin on a different schedule for whatever reason, follow their instructions carefully.

Don’t Always Inject Your Insulin in the Same Place

“Technique of insulin administration is as important as the dose administered,” says Dr. Mathew. It’s best to rotate the area where you administer insulin, because repeatedly injecting in the same place increases your risk of lipohypertrophy, a buildup of fat, protein, and scar tissue that can affect how quickly your body absorbs insulin, he says.

For rapid and long-acting insulin, rotate body parts such as the abdomen and thighs, as well as specific sites on each body part.

 For his patients, Mathew recommends injecting into the abdomen for a week, then the thighs the next week, and so on.
Intermediate-acting and premixed insulin can absorb differently from different body parts, so pick one body part for your insulin injections, but change the specific injection site on that body part regularly. They also appear cloudy and need to be rolled in your hands until they look uniform prior to injection. All other insulins should always appear clear.

Ask your health provider for their injection site recommendations as well, as these suggestions are general guidelines.

Do Check Your Blood Sugar Before Injecting

It’s best practice to check your blood sugar before using insulin, says Halverson. If your glucose is low, you may need to hold off on your insulin dose and eat something first, she says. Conversely, if you’re above your blood sugar target, you may need to add a correction dose.

There are other factors to consider as well. “The dose of insulin administered is usually based on the measured blood sugar, one’s expected activity level, and what’s being eaten,” says Mathew. If you’re planning to exercise soon, for example, it might be smart to use a smaller dose. For instructions on how to best approach dose adjustment for your specific needs, talk to your healthcare provider.

Don’t Reuse Needles

Whether you use a syringe or an insulin pen, you want to use fresh and sharp needles every time.

 “Just as important as rotating insulin administration sites, change the pen needles or insulin syringes with each insulin administration,” says Mathew.
Used needles become duller, which can make injections more painful and increase your likelihood of developing lipohypertrophy or an infection, he says. Change your needle each time, and never use someone else’s needle, as sharing can put you at risk of contracting viruses such as hepatitis and HIV.

Do Count Your Carbs

Adjusting your mealtime insulin dose to the food you’re eating is essential in managing your blood glucose levels.

Healthcare providers typically prescribe mealtime insulin doses in an insulin to carbohydrate ratio, which indicates how many units of insulin you need based on the number of carbohydrates you consume, says Halverson.

 For instance, one unit of rapid-acting insulin is often initially prescribed for 12–15 grams (g) of carbohydrates, but this amount will differ for most people with diabetes. Your ratio can also be a moving target, depending on factors like your activity level, the time of day, or your menstruation cycle. It can take a lot of experimentation and collaboration with your provider or a diabetes educator to understand your specific needs.

Successful insulin dosing also requires an understanding of the carbohydrate content in common foods and portions so you can make smart adjustments independently as needed.

“There are different ways to dose insulin and count carbs,” says Halverson. Some people, for example, dose differently for high-fiber ingredients with low net carb counts. If you’re having trouble with the plan you’re on, Halverson recommends asking your diabetes educator for a different type of insulin dosing, such as moving from fixed to flexible dosing, or vice versa.

Don’t Inject Into Muscle

Insulin should be injected into fat that lies just beneath the skin (called subcutaneous fat), says Mathew. “It’s very important that it’s not administered into the muscle or blood vessels or other tissues, as absorption can vary dramatically if it’s administered into areas other than subcutaneous tissue,” he says.

Injecting into subcutaneous fat leads to more consistent insulin absorption, whereas injecting into muscle can lead insulin to absorb in unreliable ways.

 To ensure you’re injecting into fat just beneath the skin, lift the skinfold or angle the needle 45 degrees from the skin.

Do Educate Your Friends, Family, and Coworkers

All insulin users have a risk of severe hypoglycemia (low blood glucose). Most of the time, you can treat hypoglycemia yourself by having a quick snack or drinking something sugary. But if you experience a severe episode, you’ll be unable to treat yourself and will have to rely completely on the people around you for help.

Teaching the people close to you what to do in the case of an emergency could save your life. “Time can be of the essence with hypoglycemia, and letting friends, family, and coworkers know that you’re on insulin and training them on what to do if you’re hypoglycemic is of utmost importance to prevent complications,” says Mathew.

Those close to you should know that if you're slurring your speech or becoming disoriented or unconscious, those are signs of a severe hypoglycemic episode.

 They can help you by administering emergency glucagon (available in dry nasal sprays or injections) and calling 911 immediately if they’re unsure what to do.

Don’t Forget About Exercise and Stress

Other factors beyond carbohydrates can affect your glucose control as well. For example, your blood sugar can rise as a side effect of certain medications like steroids, or from illness, psychological stress, menstrual periods, and dehydration.

 Some lifestyle factors can contribute to lower blood sugar, too, such as drinking alcohol or increasing your level of physical activity.

“You may need to adjust your insulin based on where you are in your menstrual cycle, stress levels, or new medications,” says Halverson. And if you’re planning on taking a walk after a meal, you may not need to take as much insulin for that meal, since the activity will naturally lower your blood sugar, she says.

It takes education and experience to get to the point where you’re making these adjustments effectively. If you have access to a registered dietitian-nutritionist, diabetes educator, or nurse who can spend time with you to go over all this information and personalize your insulin needs, Halverson encourages you to make an appointment.

Do Protect Your Insulin From Extreme Temperatures

Severe hot and cold temperatures can damage insulin, rendering it less effective.

 Store insulin out of direct sunlight (for example if you're at a beach or pool), and don’t keep it in a car where it can get too hot. While you can store insulin in a cooler when you’re in a hot environment, it shouldn’t directly touch ice or a freezer pack, either. If insulin freezes, don’t use it.

The Takeaway

  • Take mealtime insulin about 15 minutes before eating to allow it time to start working, and always check your blood sugar before injecting, as your dose may need to be adjusted depending on your glucose levels, planned activity, or food intake.
  • To prevent complications like lipohypertrophy, don’t inject insulin in the exact same spot repeatedly; instead, rotate injection sites across different body parts, and always inject into subcutaneous fat tissue.
  • Never reuse needles or syringes, as dull needles cause pain and increase infection risk. It’s also essential to protect your insulin from extreme temperatures (both hot and cold) to ensure its efficacy.
  • Be aware that factors like exercise, stress, other medications, and menstrual cycles can affect your blood sugar, and educate those around you on how to recognize and treat hypoglycemia to help keep you safe.

Resources We Trust

EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. 4 Ways to Take Insulin. Centers for Disease Control and Prevention. May 15, 2024.
  2. Learning to Inject. Association of Diabetes Care and Education Specialists.
  3. Calculating Insulin Dose. University of California San Francisco.
  4. Hirsch LJ et al. The Injection Technique Factor: What You Don’t Know or Teach Can Make a Difference. Clinical Diabetes. July 1, 2019.
  5. Hypoglycemia (Low Blood Sugar). Cleveland Clinic. January 31, 2023.
  6. Factors Affecting Blood Sugar. American Diabetes Association. March 2024.
  7. Managing Diabetes in the Heat. Centers for Disease Control and Prevention. May 15, 2023.
  8. Safe Storage of Insulin. American Diabetes Association. October 2023.
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Elise M. Brett, MD

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Elise M Brett, MD, is a board-certified adult endocrinologist. She received a bachelor's degree from the University of Michigan and her MD degree from the Icahn School of Medicine at Mount Sinai. She completed her residency training in internal medicine and fellowship in endocrinology and metabolism at The Mount Sinai Hospital. She has been in private practice in Manhattan since 1999.

Dr. Brett practices general endocrinology and diabetes and has additional certification in neck ultrasound and fine-needle aspiration biopsy, which she performs regularly in the office. She is voluntary faculty and associate clinical professor at the Icahn School of Medicine at Mount Sinai. She is a former member of the board of directors of the American Association of Clinical Endocrinology. She has lectured nationally and published book chapters and peer reviewed articles on various topics, including thyroid cancer, neck ultrasound, parathyroid disease, obesity, diabetes, and nutrition support.
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