If you have diabetes, your doctor may prescribe Humulin R for you.

It’s a prescription drug that’s used in adults and children with either type 1 or type 2 diabetes. It helps manage blood sugar levels.

To learn more about diabetes and how Humulin R treats it, see the “What is Humulin R used for?” section below.

Humulin R basics

Humulin R comes as a solution inside vials and disposable, prefilled injection pens called a KwikPens.

You’ll take it as an injection under your skin. Humulin R can also be given by your doctor as an intravenous (IV) infusion. (This is an injection given into a vein over a period of time.)

Humulin R is a type of regular insulin. It contains the active drug insulin human, which is a biologic drug. Biologics are made from parts of living cells. Humulin R isn’t available in a biosimilar form. (Biosimilars are like generic drugs. Unlike generics, which are made for nonbiologic drugs, biosimilars are made for biologic drugs.)

You can get Humulin R from your pharmacy with a prescription. You can also purchase it over the counter (OTC). (The OTC form doesn’t require a prescription from your doctor.)

Read on to learn about Humulin R’s side effects, uses, and more.

Your doctor will recommend the dosage of Humulin R that’s right for you. Below are commonly used dosages, but always take the dosage your doctor prescribes.

Forms and strengths

Humulin R comes as a solution. You’ll take it as an injection under your skin. The drug can also be given by your doctor as an intravenous (IV) infusion. (This is an injection given into a vein over a period of time.)

Humulin R is available in two strengths:

  • U-100, which contains 100 units of insulin per milliliter (mL)
  • U-500, which contains 500 units of insulin per mL

The U-100 strength of Humulin R comes in 3-mL and 10-mL vials. You’ll use insulin syringes to take doses of the drug from vials.

The U-500 strength of Humulin R comes in two forms:

  • 20-mL vials that you’ll use with insulin syringes
  • 3-mL disposable, prefilled injection pens called a KwikPens

Recommended dosages

You’ll likely take Humulin R about 30 minutes before you eat. Your doctor will tell you exactly how much to take for each dose.

Your dosage of Humulin R depends on:

  • the strength of Humulin R you use
  • whether you have type 1 or type 2 diabetes
  • other medications you take, including other types of insulin
  • other medical conditions you have

Sliding scale dosage

Your doctor may determine your dosage of Humulin R using a sliding scale. This method is commonly used to manage blood sugar levels in people staying at a hospital.

With a sliding scale, your exact dosage of Humulin R may depend on:

When using a sliding scale, your doctor will suggest either a low dose, moderate dose, or high dose of insulin. If you have questions about sliding scales with Humulin R, talk with your doctor.

Questions about Humulin R’s dosage

Here’s a list of answers to common questions related to taking Humulin R.

  • What if I miss a dose of Humulin R? You’ll typically use Humulin R 30 minutes before you start eating a meal. If you forget your dose, you can check your blood sugar level to decide if you need insulin. Then, you can either take your missed dose or wait until you would normally take the next dose. If you aren’t sure whether to take a dose of Humulin R or skip it, talk with your doctor. They can tell you what your blood sugar level should be after you’ve eaten.
  • Will I need to use Humulin R long term? It’s possible. Diabetes usually requires long-term treatment, and Humulin R can be used long term. If you and your doctor decide that Humulin R is safe and effective for you, you’ll likely take it long term.
  • How long does Humulin R take to work? Humulin R starts to manage your blood sugar level within 30 minutes of being injected.

Find answers to some commonly asked questions about Humulin R.

What’s the peak, duration, and onset time of Humulin R?

Below are the typical peak, duration, and onset times for Humulin R:

  • Peak time. Each dose of Humulin R reaches its peak (maximum) effect about 3 hours after it’s injected.
  • Duration time. The duration of Humulin R’s effect is about 8 hours. (Duration refers to how long the drug keeps working in your body after it’s been injected.) In other words, each dose of Humulin R keeps working in your body for about 8 hours after you inject it.
  • Onset time. The onset of Humulin R is about 30 minutes. This means the drug begins working in your body about 30 minutes after you inject it.

If you have more questions about the peak, duration, and onset of Humulin R, talk with your doctor or pharmacist.

How should you store Humulin R? How long can it be unrefrigerated, and does it expire?

The way you should store Humulin R, and its expiration date will vary depending on a few factors.

Unopened vials of Humulin R can be stored at room temperature below 86°F (30°C) for up to 31 days. Unopened injection pens of Humulin R can be stored at the same temperature for up to 28 days.

But both vials and pens can be stored until their expiration date if they’re kept in a refrigerator at a temperature between 36°F and 46°F (2°C to 8°C).

Once opened, Humulin R vials can be stored for up to 31 days at room temperature or in a refrigerator. But opened Humulin R injection pens should be stored at room temperature. They can be kept for up to 28 days.

Be sure to store Humulin R vials and injection pens away from light. Throw away any vials that have been open for more than 31 days. And discard injection pens that have been opened for more than 28 days.

Ask your doctor or pharmacist if you have questions about safely disposing leftover medication or injection supplies.

Is Humulin R a short-acting insulin?

Yes, Humulin R is a short-acting insulin. Humulin R is considered “short-acting” because it takes about 30 minutes to start working after it’s injected. So, you’ll take doses of Humulin R about 30 minutes before your meals.

How does Humulin R work?

Humulin R is used in adults and children with either type 1 or type 2 diabetes. It helps manage blood sugar levels.

Diabetes is a condition that causes high blood sugar. Normally, your pancreas releases a hormone called insulin to help lower your blood sugar levels. But with diabetes, your body either can’t use the insulin it makes, or it doesn’t make enough insulin.

Humulin R is a type of regular insulin. Its mechanism of action (how it works) is to replace or add to your body’s natural insulin.

Humulin R lowers your blood sugar levels by:

  • keeping your body from breaking down proteins and fats so that it breaks down blood sugar instead
  • preventing your liver from making more blood sugar
  • helping your fat cells and muscle cells take up sugar from your blood

Is Humulin R used for bodybuilding or muscle growth?

No, Humulin R isn’t approved for bodybuilding or muscle growth.

Insulin, such as Humulin R, helps muscles quickly take up sugar and nutrients from your blood. This gives muscles energy, such as during a workout. It can also help stimulate new muscle growth.

But insulin can also cause serious side effects, including low blood sugar level. (To learn more about this, see the “What are Humulin R’s side effects?” section below.) Because of this risk, Humulin R shouldn’t be used for bodybuilding or muscle growth.

If you have more questions about using Humulin R for these purposes, talk with your doctor.

Can you mix Humulin R and Lantus?

No, you should not mix Humulin R in the same syringe with insulin glargine (Lantus). Doing this could affect how each drug works to manage your blood sugar level.

If you have questions about using Humulin R with other insulins, talk with your doctor or pharmacist.

Both Humulin R and Humulin N are used in adults and children with either type 1 or type 2 diabetes. And both medications contain the active drug insulin human. These medications help manage blood sugar levels.

Humulin R is a short-acting insulin, while Humulin N is an intermediate-acting insulin. This means they work over different lengths of time inside your body.

To learn more about these drugs, see this detailed comparison. Also, talk with your doctor about which drug is right for you.

Humulin R and Novolin R are both short-acting insulins. They’re used in adults and children with either type 1 or type 2 diabetes. These medications help manage blood sugar levels.

Both Humulin R and Novolin R contain the active drug insulin human.

If you’d like to know more about these medications, see this side-by-side breakdown. Check with your doctor to find out more information.

Both Humulin R and Humalog are used in adults and children with either type 1 or type 2 diabetes. These medications help manage blood sugar levels.

Humulin R contains the active drug insulin human, while Humalog contains the active drug insulin lispro.

Check out this article to see how Humulin R and Humalog compare. Let your doctor know if you’d like more information above which drug is best for your condition.

Like most drugs, Humulin R may cause mild or serious side effects. The lists below describe some of the more common side effects that Humulin R may cause. These lists don’t include all possible side effects.

Keep in mind that side effects of a drug can depend on:

  • your age
  • other health conditions you have
  • other medications you take

Your doctor or pharmacist can tell you more about the potential side effects of Humulin R. They can also suggest ways to help reduce side effects.

Mild side effects

Here’s a short list of some of the mild side effects that Humulin R can cause. To learn about other mild side effects, talk with your doctor or pharmacist, or read Humulin R’s prescribing information.

Mild side effects of Humulin R that have been reported include:

Mild side effects of many drugs may go away within a few days or a couple of weeks. But if they become bothersome, talk with your doctor or pharmacist.

* For more information about this side effect, see the “Side effect focus” section below.

Serious side effects

Serious side effects from Humulin R can occur, but they aren’t common. If you have serious side effects from Humulin R, call your doctor right away. However, if you think you’re having a medical emergency, you should call 911 or your local emergency number.

Serious side effects of Humulin R that have been reported include:

* For more information about this side effect, see the “Side effect focus” section below.

Side effect focus

Learn more about some of the side effects Humulin R may cause.

Weight gain

You may gain weight while you’re taking Humulin R. This was one of the most common side effects in studies of the drug.

You may also gain weight if you have swelling, which is another common side effect of Humulin R. Swelling from Humulin R usually affects your feet, legs, arms, or hands.

What might help

It’s important to tell your doctor if you have weight gain while you’re taking Humulin R.

They may need to adjust your dosage of the drug if your weight changes during treatment. Your doctor can also suggest ways to manage your weight with fitness and nutrition while you’re taking Humulin R.

Injection site reactions

You may have injection site reactions while you’re taking Humulin R. These were common in studies of the drug.

You may have any of the following reactions around the area where you inject Humulin R:

  • bruising
  • buildup of protein under your skin
  • itching
  • pain
  • rash
  • thickened skin or pits in your skin

What might help

It’s important to inject each dose of Humulin R into in a new area of skin. You can inject Humulin R into your belly, buttocks, upper arms, or upper thighs. Changing your injection site lowers your risk for these reactions.

If you have any of the reactions listed above while you’re taking Humulin R, don’t inject the drug into the area until it has healed.

If you continue to have bothersome injection site reactions while using Humulin R, talk with your doctor. They can recommend ways to help lessen this side effect.

Low blood sugar level

You may have low blood sugar levels while you’re taking Humulin R. This is the most common side effect of all insulin medications, including Humulin R.

Low blood sugar happens when your blood sugar level drops below a certain healthy level. For most people with diabetes, a normal blood sugar level is above 70 milligrams per deciliter (mg/dL).

With low blood sugar, you may have the following symptoms:

  • dizziness
  • headache
  • pale-looking skin
  • sweating or shaking
  • trouble concentrating

In severe cases, your blood sugar could be so low that you have seizures. You may also lose consciousness, meaning you’re unable to respond to touch or sound.

What might help

Your doctor will tell you how often you should check your blood sugar level while you’re taking Humulin R. This can help prevent low blood sugar levels.

If you have low blood sugar, the American Diabetes Association recommends the 15-15 rule. To follow this, you’ll eat at least 15 grams (g) of fast-acting carbohydrates within 15 minutes of having low blood sugar.

Examples of things to consume for 15 g of fast-acting carbohydrates include:

  • glucose liquid, gel, tablets, or powder
  • hard candy; read the candy’s label to learn how much contains 15 g of glucose
  • 4 ounces of regular (not diet) soda
  • 4 ounces of fruit juice

Tell your doctor if you have a low blood sugar level while you’re taking Humulin R. They can help you understand what caused it. And they can suggest ways to help you avoid another episode.

If you have severe low blood sugar, your blood sugar level may be so low that you need someone’s help to treat it. Be sure a co-worker, friend, family member, or caregiver knows how to recognize and treat this condition.

Severe low blood sugar is a medical emergency, and it should be treated right away. You or someone else should call 911 or your local emergency phone number if you have symptoms of this condition.

Allergic reaction

Some people may have an allergic reaction to Humulin R.

Symptoms of a mild allergic reaction can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)

A more severe allergic reaction is rare but possible. Symptoms of a severe allergic reaction can include swelling under your skin, typically in your eyelids, lips, hands, or feet. They can also include swelling of your tongue, mouth, or throat, which can cause you breathing trouble.

Call your doctor right away if you have an allergic reaction to Humulin R. But if you think you’re having a medical emergency, call 911 or your local emergency number.

Costs of prescription drugs can vary depending on many factors. These factors include what your insurance plan covers and which pharmacy you use. To find current prices for Humulin R U-100 and Humulin R U-500 in your area, visit GoodRx.com.*

Humulin R is also available in an over-the-counter (OTC) form that doesn’t require a prescription. The cost of the OTC form may be different from the cost of the prescription form. Talk with your doctor if you’d like to know about using OTC Humulin R.

If you have questions about how to pay for your prescription, talk with your doctor or pharmacist. You can also visit the Humulin R manufacturer’s website to see if they have support options.

* To learn more about these available strengths of Humulin R, see the “What is Humulin R’s dosage?” section above.

Your doctor will explain how you should take Humulin R. They’ll also explain how much to take and how often. Be sure to follow your doctor’s instructions.

Taking Humulin R

Humulin R comes as a solution. You’ll take it as an injection under your skin. The drug can also be given by your doctor as an intravenous (IV) infusion. (This is an injection given into a vein over a period of time.)

Humulin R solution comes in:

Your doctor will show you how to give injections of Humulin R to yourself.

It’s important that you inject each dose of Humulin R into in a new area. You can inject the drug into any of the following administration sites:

  • belly
  • buttocks
  • upper arms
  • upper thighs

Rotating your injection sites lowers your risk for having injection site reactions. For details about this side effect, see the “What are Humulin R’s side effects?” section above.

Taking Humulin R with food

You should take Humulin R 30 minutes before eating a meal.

Questions for your doctor

You may have questions about Humulin R and your treatment plan. It’s important to discuss all your concerns with your doctor.

Here are a few tips that might help guide your discussion:

  • Before your appointment, write down questions such as:
    • How will Humulin R affect my body, mood, or lifestyle?
  • Bring someone with you to your appointment if doing so will help you feel more comfortable.
  • If you don’t understand something related to your condition or treatment, ask your doctor to explain it to you.

Remember, your doctor and other healthcare professionals are available to help you. And they want you to get the best care possible. So, don’t be afraid to ask questions or offer feedback on your treatment.

If you have diabetes, your doctor may prescribe Humulin R.

It’s a prescription drug that’s used in adults and children with either type 1 or type 2 diabetes. It helps manage blood sugar levels.

Diabetes is a condition that causes high blood sugar levels. Blood sugar is the main source of energy for your body’s cells. To help blood sugar get into your body’s cells, your pancreas releases a hormone called insulin.

But with diabetes, your body either can’t use the insulin it makes, or your body doesn’t make enough insulin. Over time, this can cause too much sugar to stay in your blood.

Having a high level of blood sugar over a long period of time can cause serious problems, including kidney disease and heart disease.

Humulin R is a type of regular insulin. It works by replacing or adding to the insulin your body makes naturally.

When considering Humulin R, it’s important to talk with your doctor about your overall health. Also tell them about any medications you take and any medical conditions you have.

These factors and others are described in more detail below.

Interactions

Taking medications, vaccines, foods, and other things with a certain drug can affect how the drug works. These effects are called interactions.

Before taking Humulin R, be sure to tell your doctor about all the medications you take. This includes prescription and over-the-counter types. Also describe any vitamins, herbs, or supplements you use. Your doctor or pharmacist can tell you about any interactions these items may cause with Humulin R.

Interactions with drugs or supplements

Humulin R can interact with several types of drugs. These drugs include:

This list does not contain all types of drugs that may interact with Humulin R. Your doctor or pharmacist can tell you more about these interactions and any others that may occur with use of Humulin R.

Warnings

Humulin R may not be right for you if you have certain medical conditions or other factors that affect your health. Talk with your doctor about your health history before you take Humulin R. Factors to consider include those in the list below.

  • Low blood sugar level. You shouldn’t use Humulin R during an episode of low blood sugar. This is because Humulin R can cause low blood sugar. For details, see the “What are Humulin R’s side effects?” section above.
  • Low potassium level. Before using Humulin R, tell your doctor if you have a low level of potassium. Humulin R can cause low potassium, which could worsen your condition. Also tell your doctor about all other medications you take. They can advise if any medications you take may also increase your risk for this side effect.
  • Allergic reaction. If you’ve had an allergic reaction to Humulin R or any of its ingredients, you shouldn’t take Humulin R. Ask your doctor what other medications are better options for you.
  • Use of thiazolidinediones (TZDs). Before taking Humulin R, tell your doctor if you take diabetes drugs called TZDs. Examples of TZDs include rosiglitazone (Avandia) and pioglitazone (Actos). When taken with TZDs, Humulin R can increase your risk for swelling. And this swelling could cause new or worsening heart failure. Your doctor can advise if it’s safe for you to use Humulin R if you take these medications.

Humulin R and alcohol

Alcohol can affect how well Humulin R works to manage your blood sugar levels. This is because alcohol can change your blood sugar levels. For this reason, it’s best to avoid drinking alcohol while you’re taking Humulin R.

Keep in mind that some liquid medications, such as liquid Nyquil, contain small amounts of alcohol. If possible, you may want to avoid taking medications that contain alcohol while you’re taking Humulin R.

Before starting Humulin R, tell your doctor about all medications you’re taking. They can advise if those drugs contain alcohol. If you drink alcohol, talk with your doctor about how much is safe for you to drink while you’re taking Humulin R.

Pregnancy and breastfeeding

There aren’t any known issues with the safety of taking Humulin R while pregnant or breastfeeding. The drug is generally considered safe for use during these times.

If you’re pregnant or breastfeeding, talk with your doctor about the benefits and risks of taking Humulin R.

Don’t take more Humulin R than your doctor prescribes. Using more than this can lead to serious side effects.

Symptoms of overdose

Symptoms caused by an overdose can include:

What to do in case you take too much Humulin R

Call your doctor if you think you’ve taken too much Humulin R. You can also call 800-222-1222 to reach the American Association of Poison Control Centers, or use its online resource. However, if you have severe symptoms, immediately call 911 (or your local emergency number) or go to the nearest emergency room.

If you have diabetes, your doctor may prescribe Humulin R for you.

If you have questions about taking this drug, talk with your doctor or pharmacist. Your doctor can tell you about other treatment options for diabetes.

Below are a few articles that you might find helpful.

Some questions to ask your doctor about Humulin R may include:

  • How should I store Humulin R while I’m traveling?
  • How often should I check my blood sugar level while I’m taking Humulin R?
  • What should I do if I notice thickened skin or pits in my skin after injecting Humulin R?

To learn more about the uses of Humulin R, you can subscribe to Healthline’s type 2 diabetes newsletter.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.