Queen Buyalos is a pharmacist and freelance medical writer in Virginia. Queen has a son who is a childhood cancer survivor. To encourage health and wellness, she started her blog, MommyQueendom. She enjoys spending time with her family, traveling, trying new foods, and playing her kids’ new favorite board game, “10 days in Africa.”

Erika Prouty, PharmD, is a professional community pharmacist who aids patients in medication management and pharmacy services in North Adams, Massachusetts.

Humulin R is a prescription drug used to lower blood sugar in people with high blood sugar (diabetes). It’s a short-acting insulin drug available as a solution for injection or infusion.

Humulin R works by allowing blood sugar (glucose) to enter your cells and be used for energy by your body. This lowers your blood sugar. 

Humulin R is usually used in combination with intermediate- or long-acting insulin or given through a continuous insulin infusion pump under the skin. A blood test, the hemoglobin A1C (HbA1c) test, is used to measure how well this drug is working for you. It measures your average blood sugar levels over the last three months. The goal is to get to an HbA1c of less than 7% as quickly as possible by safely adjusting your dosage.

Generic Name: Insulin Human Regular

Brand Name(s): Humulin R

Controlled Substance: N/A

Administration Route: Injection, Intravenous

Active Ingredient: Insulin Human Regular

Dosage Form(s): Subcutaneous injection, Intravenous infusion

Humulin R commonly treats diabetes type 1 and diabetes type 2 in combination with other insulins or other medicines. According to the World Health Organization, in 2014, 422 million people had diabetes (types I and II combined) worldwide. In 2017, 9 million people had type 1 diabetes worldwide. According to the American Diabetes Association, in 2019, 37.3 million Americans (11.3% of the population) had diabetes. Around 1.9 million Americans have type 1 diabetes, including around 244,000 children and adolescents.

Regular insulin is a short-acting insulin. Different people will need different amounts of this medicine, depending on their weight, meals per day, exercise level, etc. Your healthcare provider will supervise any dose change to avoid hypoglycemia (low blood sugar).

Wash your hands before using. Inject into the fatty areas of the skin in your stomach, thigh, buttocks, or outer upper arm area. Use as directed 30 minutes before meals. Rotate injection sites with each shot to avoid lipodystrophy (fat loss in some areas of the body and fat gain in other areas like the liver) or localized cutaneous amyloidosis (abnormal protein growths under the skin). Also keep the following in mind:

Store unopened vials in a refrigerator (36 to 46 degrees F) until the expiration date. Do not freeze. Do not use if frozen. Keep away from heat and light.

Humulin R U-100: Opened vials may be stored for 31 days at room temperature (less than 86 degrees F) or in a refrigerator. Throw out after 31 days from opening.

Humulin R U-500: Opened vials may be stored for 40 days at room temperature (less than 86 degrees F) or in a refrigerator. Throw out after 40 days from opening.

KwikPen: Opened vials may be stored for 28 days at room temperature (less than 86 degrees F) or in a refrigerator. Throw out after 28 days from opening.

Keep your medications out of the reach of children and pets, ideally locked.

If you plan to travel with Humulin R, get familiar with your final destination's regulations. In general, be sure to make a copy of your Humulin R prescription. If possible, keep your medication in its original container from your pharmacy with your name on the label. If you have any questions about traveling with your medicine, be sure to ask your pharmacist or healthcare provider.

Discard all unused and expired drugs, but do not pour them down the drain or toilet. Ask your pharmacist or healthcare provider about the best ways to dispose of this medicine. And check out drug take-back programs in your area.

The time it takes to work depends on many factors like:

It takes U-100 about 30 minutes to start working if given under the skin. If administered into your veins, it takes U-100 between 10 and 15 minutes to begin working. U-500 takes less than 15 minutes to work.

Off-label Humulin is used to treat:

This is not a complete list of side effects and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your pharmacist or a healthcare provider. You may report side effects to the Food and Drug Administration (FDA) at fda.gov/medwatch or 800-FDA-1088.

Humulin R may or may not cause side effects in some people. Contact your healthcare provider right away if your side effects do not go away or become irritating. The following are some of the most common side effects of Humulin R:

Contact your healthcare provider right away if you develop any signs of a severe reaction. Call 911 if your symptoms feel life-threatening.

Serious side effects and their symptoms include the following.

Signs of low potassium such as:

Signs of low blood sugar such as: 

Humulin R may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your healthcare provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

The following modifications (changes) should be kept in mind when using Humulin R:

Severe allergic reaction: Do not take Humulin R if you’re hypersensitive to regular insulin or any of its ingredients.

Pregnancy: Insulin and food needs are likely to increase as pregnancy continues. Your healthcare provider may increase or adjust your insulin dosage, discuss your food needs, and frequent blood sugar monitoring. Discuss with your healthcare provider if you are or plan to become pregnant.

Breastfeeding: Taking insulin while breastfeeding has not shown low blood sugar in breastfeeding babies. Your food and insulin needs may change during breastfeeding. Talk with your healthcare provider if you plan to breastfeed.

Children: Insulin needs in children may change based on several different factors. Children may also sometimes be unaware when they have low blood sugar. Talk with your child's healthcare provider to discuss any changes needed.

Kidney problems: Frequent glucose monitoring and insulin dose reduction may be needed in people with kidney problems.

Liver problems: Frequent glucose monitoring and insulin dose reduction may be needed in people with liver problems.

Exercise: Exercise tends to lower blood glucose levels. Your insulin may need to be adjusted accordingly.

Illness: Illness may change your blood glucose levels. Your insulin may need to be adjusted accordingly.

Travel: If you plan to travel across more than two time zones, talk to your healthcare provider about any changes needed for your insulin schedule.

Other medications: Insulin requirements may increase if you take medicines that increase blood sugar (e.g., corticosteroids, oral contraceptives, thyroid replacement). Insulin requirements may decrease if you take medicines that lower blood sugar or impact your body's response to insulin (alcohol, antidiabetic agents (blood sugar lowering), salicylates like aspirin, some antidepressants, some kidney and blood pressure medicines, and sulfa antibiotics). It's important to let your healthcare provider know what other medicines you take or plan to take when you're on insulin. This includes over-the-counter, nonprescription products, vitamins, herbs or plant-based medicines.

If you accidentally forgot your Humulin R dose, take it as soon as you remember. Make sure that you know what to do if you miss a dose. If you are not sure, call your healthcare provider for guidance. Don't try to double up to make up for the missed dose.

Try to find ways to help yourself remember to routinely take the medication that works for you.

Overdose symptoms may include hypoglycemia (very low blood sugar). Severe cases may include seizures or coma.

It's a good idea to have a Glucagon injection pen for cases where your blood sugar may be extremely low. It's important for you—and also for those people you spend a lot of time with—to know how to use a a Glucagon injection in case your blood sugar becomes so low that you became unconscious.

If you think that you're experiencing an overdose or life-threatening symptoms, seek immediate medical attention.

If you think you or someone else may have overdosed on Humulin R, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking Humulin R, call 911 immediately.

Never share insulin needles or syringes with others under any circumstances. It is not safe for one pen to be used for more than one person. Sharing needles can result in transmission of hepatitis viruses, HIV, or other bloodborne illnesses.

Your doctor will want to check your progress at regular visits, especially during the first few weeks you are using this medicine. Blood tests may be needed to check for unwanted effects.

It is very important to follow carefully any instructions from your health care team about:

In case of emergency: There may be a time when you need emergency help for a problem caused by your diabetes. You need to be prepared for these emergencies. It is a good idea to:

This medicine may cause serious allergic reactions, including anaphylaxis. Anaphylaxis can be life-threatening and requires immediate medical attention. Tell your doctor right away if you have a rash, itching, swelling of the face, tongue, and throat, trouble breathing, or chest pain after you get the injection.

Using this medicine together with other diabetes medicine (eg, pioglitazone, rosiglitazone, Actos®, Actoplus Met®, Avandia®) may cause serious heart problem or edema (fluid retention). Check with your doctor immediately if you are rapidly gaining weight, having shortness of breath, chest pain or discomfort, extreme tiredness or weakness, trouble breathing, uneven heartbeat, or excessive swelling of the hands, wrist, ankles, or feet.

You may have some skin redness, rash, itching, or swelling at the injection site. If this irritation is severe or does not go away, call your doctor. Do not inject this medicine into a skin area that is red, swollen, or itchy.

This medicine may make you dizzy or drowsy. Make sure you know how you react to this medicine before you drive, use machines, or do other jobs that require you to be alert.

Too much insulin human regular can cause hypoglycemia (low blood sugar). Low blood sugar also can occur if you use insulin human regular with another antidiabetic medicine, changes in insulin regimen (eg, insulin strength, type of insulin, injection site), delay or miss a meal or snack, exercise more than usual, or drink alcohol. Symptoms of low blood sugar must be treated before they lead to unconsciousness (passing out). Different people may feel different symptoms of low blood sugar. It is important that you learn which symptoms of low blood sugar you usually have so that you can treat it quickly.

Symptoms of low blood sugar include anxiety, behavior change similar to being drunk, blurred vision, cold sweats, confusion, difficulty in thinking, dizziness or lightheadedness, drowsiness, excessive hunger, fast heartbeat, headache, irritability or abnormal behavior, nervousness, nightmares, restless sleep, shakiness, slurred speech, and tingling in the hands, feet, lips, or tongue.

If symptoms of low blood sugar occur, eat glucose tablets or gel, corn syrup, honey, or sugar cubes, or drink fruit juice, non diet soft drink, or sugar dissolved in water to relieve the symptoms. Also, check your blood for low blood sugar. Get to a doctor or a hospital right away if the symptoms do not improve. Someone should call for emergency help immediately if severe symptoms such as convulsions (seizures) or unconsciousness occur. Have a glucagon kit available, along with a syringe and needle, and know how to use it. Members of your household also should know how to use it.

Hyperglycemia (high blood sugar) may occur if you do not take enough or skip a dose of your medicine, overeat or do not follow your meal plan, changes in insulin regimen, have a fever or infection, or do not exercise as much as usual. High blood sugar can be very serious and must be treated right away. It is important that you learn which symptoms you have in order to treat it quickly. Talk to your doctor about the best way to treat high blood sugar.

Symptoms of high blood sugar include blurred vision, drowsiness, dry mouth, flushed, dry skin, fruit-like breath odor, increased urination, ketones in the urine, loss of appetite, stomachache, nausea, or vomiting, tiredness, troubled breathing (rapid and deep), unconsciousness, and unusual thirst.

If symptoms of high blood sugar occur, check your blood sugar level and then call your doctor for instructions.

This medicine may cause low levels of potassium in your blood. Do not use medicines, supplements, or salt substitutes that contain potassium unless you have discussed this with your doctor.

Do not take Humulin R if you’re hypersensitive to regular insulin or any of its ingredients.

Do not use this medicine during episodes of hypoglycemia.

Certain medications may affect how well Humulin R works.

Drugs that may increase Humulin R's blood sugar lowering effects:

Drugs that may reduce Humulin R's blood sugar lowering effects:

Drugs that may increase or decrease Humulin R's blood sugar lowering effects:

Pentamidine may cause low blood sugar, sometimes followed by high blood sugar.

Drugs that may mask the signs of hypoglycemia:

For more detailed information about medication interactions with Humulin R, talk with your pharmacist or healthcare provider.

And be sure to talk with your healthcare provider about any other medicines that you take or plan to take, including over-the-counter, nonprescription products, vitamins, herbs or plant-based medicines.

Other insulins used to treat diabetes like Humulin R include:

Note that there are rapid-, short-, intermediate-, long-, and ultra long-acting insulins. It's important to know the differences because they change blood sugar levels differently. They include:

It’s used to lower the blood sugar of people with high blood sugar (e.g., diabetes).

Some common side effects include:

Contact your healthcare provider if you do not know what to do if you miss your dose.

While Humulin R effectively controls blood sugar, it may be harder to control your levels when you have a fever, an injury, a surgery, or are stressed. Here are a few tips to keep in mind:

Consider working with a team that includes a registered dietitian nutritionist (RD or RDN)—and particularly one that's a Certified Diabetes Care and Education Specialist (CDCES). CDES RDs/RDNs can help you explore your eating, movement, medication habits and more. They can help you build your toolkit and capacity to avoid spikes in blood sugar and help you feel good. Navigating blood sugar control and your eating patterns can be challenging, but you don't have to do this alone.

Verywell Health's drug information is meant for educational purposes only and is not intended to replace medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

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Food and Drug Administration. Humulin R label.

Qaseem A, Wilt TJ, Kansagara D, Horwitch C, Barry MJ, Forciea MA. Hemoglobin A1c targets for glycemic control with pharmacologic therapy for nonpregnant adults with type 2 diabetes mellitus: a guidance statement update from the American College of Physicians. Ann Intern Med. 2018;168(8):569-576. doi:10.7326/M17-0939

American Diabetes Association. Statistics about diabetes.

American Diabetes Association. Insulin basics.

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