If you have diabetes, your doctor may suggest Humulin R as a treatment option.

It’s a medication that’s available both over the counter and with a prescription.* It’s used to manage blood sugar levels that occur with type 1 or type 2 diabetes in adults and children. If you and your doctor agree that Humulin R is working well for you, you’ll likely use it long term.

Humulin R is a regular- or short-acting form of insulin. The active ingredient in Humulin R is insulin human. The active ingredient is what makes the drug work. Insulin human is a type of biologic medication (a drug made from parts of living organisms).

Humulin R comes as a liquid solution that’s given by subcutaneous injection (an injection under your skin). It’s available in these forms:

  • multiple-dose vials
  • prefilled KwikPens

Humulin R may also be given as an intravenous (IV) infusion (an injection into your vein given over time). This is done by your doctor or another healthcare professional, usually in a hospital or clinic. Humulin R isn’t used in this way to manage blood sugar levels long term.

For more information about Humulin R, including details about its uses, see this in-depth article on the drug.

Like other drugs, Humulin R can cause mild to serious side effects (also known as adverse effects). Keep reading to learn more.

* You can buy Humulin R without a prescription. But you may want to ask your doctor for one if you have insurance that covers some or all of your drug costs. Either way, you should talk with your doctor before starting Humulin R.

Some people may experience mild to serious side effects during their Humulin R treatment. Examples of commonly reported side effects include:

* To learn more about this side effect, see the “Side effects explained” section below.

These side effects won’t happen to everyone who uses Humulin R, though. And these aren’t the only side effects that Humulin R can cause. Read on to learn more about many of the drug’s mild to serious side effects.

Like most medications, treatment with Humulin R can cause mild side effects.

Examples that have been reported with this drug include:

* To learn more about this side effect, see the “Side effects explained” section below.

In most cases, these side effects should be temporary. And some may be easily managed. But if you have symptoms that are ongoing or bother you, talk with your doctor or pharmacist. And do not stop Humulin R treatment unless your doctor recommends it.

Humulin R may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Humulin R, visit MedWatch.

Serious side effects can occur with Humulin R treatment. These include:

* To learn more about this side effect, see the “Side effects explained” section below.

Of the side effects listed above, hypoglycemia (low blood sugar) is the most common.

If you develop serious side effects during treatment with Humulin R, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Get answers to some frequently asked questions about Humulin R’s side effects.

Can Humulin R insulin cause any long-term adverse effects?

No, Humulin R insulin isn’t known to cause any long-term adverse effects (commonly known as side effects).

Long-term side effects can mean those that begin:

  • during your treatment and continue for a long time (sometimes after treatment ends)
  • after you’ve used the drug for a long time
  • after treatment is finished

Long-term side effects weren’t reported in Humulin R’s studies, though.

Talk with your doctor or pharmacist if you have any questions about long-term effects of Humulin R treatment.

How do the side effects of Humulin R U-500 compare with those of U-100?

Humulin R is available in two strengths:

  • U-100: This form contains 100 units of insulin per 1 milliliter (mL) of solution (100 U/mL).
  • U-500: This form contains 500 units of insulin per 1 mL of solution (500 U/mL).

Side effects of the two strengths are expected to be the same, according to studies of these drugs.

Can Humulin R increase my risk of urinary tract infections?

No, Humulin R isn’t known to increase your risk of urinary tract infection (UTI). This side effect wasn’t reported in the drug’s studies.

Other medications used to treat diabetes may increase your risk of UTI, though. Examples include sodium-glucose transport protein 2 (SGLT2) inhibitors, such as:

SGLT2 drugs increase the risk of UTI. But Humulin R isn’t known to increase the amount of sugar in your urine or increase your risk of UTI.

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

Low blood sugar

Treatment with Humulin R may cause hypoglycemia (low blood sugar). This is a possible side effect of every medication used to treat diabetes.

Low blood sugar is the most common side effect of drugs containing insulin, including Humulin R. Low blood sugar caused by Humulin R may be mild or serious but tends to be mild when it occurs.

Symptoms of mild low blood sugar can include:

While rare, low blood sugar caused by Humulin R can be severe. This risk increases if you:

  • have liver or kidney problems
  • fast or skip a meal
  • change your level of physical activity (for example, start a new exercise routine)
  • use Humulin R together with other medications for diabetes

Symptoms of severe low blood sugar can include:

In extreme cases, severe low blood sugar can lead to death.

What might help

During your treatment with Humulin R, you’ll check your blood sugar level with a blood glucose monitor. Your doctor will advise you on how often you should do this throughout your treatment.

Before you start Humulin R, talk with your doctor about what to do if your blood sugar level drops too low. When it’s mild, low blood sugar can be treated at home with quick-acting carbohydrates, including:

  • 1 tablespoon of honey
  • three or four pieces of hard candy
  • 1/2 cup of juice or regular soda (not diet)
  • glucose (sugar) tablets

If you have severe low blood sugar, your doctor may prescribe glucagon for you. This is a medication that quickly raises blood sugar levels that are dangerously low.

Talk with your doctor about a treatment plan in case you have low blood sugar while being treated with Humulin R. But if you’re having symptoms of severe low blood sugar or any symptoms that feel life threatening, call 911 or go to the closest emergency room.

Injection site reaction, including thickened skin or skin pits

Humulin R is given by subcutaneous injection (an injection under your skin). This can cause an injection site reaction, which is a side effect that happens where you inject the drug. It’s not known how often this side effect occurred in studies.

Injection site reaction caused by Humulin R can include:

  • itchy skin
  • bleeding
  • pain
  • swelling
  • skin reddening or discoloration
  • skin pits or lumps
  • thickened skin

What might help

To reduce your risk of injection site reaction, change the site where you inject Humulin R. Do not use the same spot for two or more doses in a row.

Humulin R may be injected under your skin into your:

  • upper arms (triceps)
  • belly
  • buttocks
  • thighs

Do not inject into the same spot each time. If you use the same body part, inject the dose into a different area of skin. For example, if you injected your last dose on the right side of your belly, it’s OK to inject your next dose on the left side.

You should also avoid injecting this drug into skin that is:

  • thickened, pitted, or lumpy
  • tender
  • bruised
  • scarred or damaged
  • scaly or hard

If you have bothersome injection site reactions during treatment with Humulin R, talk with your doctor or pharmacist. They can observe how you inject the drug and possibly provide advice on techniques that could reduce your symptoms. They may also suggest you stop treatment with Humulin R and try a different option for managing your blood sugar.

Weight gain

It’s possible that you’ll have weight gain as a side effect from Humulin R. It’s not known how often this occurred or how much weight people gained on average in the drug’s studies. It is among the more common side effects the drug may cause, though.

But keep in mind that weight gain is a side effect caused by any drug that contains insulin. It’s not unique to Humulin R.

What might help

Talk with your doctor if you’re concerned about weight gain and Humulin R. They can suggest ways for you to reach or maintain a weight that’s healthy for you.

Allergic reaction

Like most drugs, Humulin R can cause an allergic reaction in some people. It’s not known exactly how often this side effect occurred in the drug’s studies, though.

Symptoms can be mild or serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a product to manage your symptoms, for example:

  • an over-the-counter oral antihistamine, such as Benadryl (diphenhydramine)
  • a topical product, such as hydrocortisone cream

If your doctor confirms you’ve had a mild allergic reaction to Humulin R, they’ll decide if you should continue using it.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to Humulin R, they may have you switch to a different treatment.

Keeping track of side effects

During your Humulin R treatment, consider keeping notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start taking new drugs or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how it affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Taking notes and sharing them with your doctor will help them learn more about how Humulin R affects you. They can then use this information to adjust your treatment plan if needed.

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 starting Humulin R. Below are a few factors to consider.

Heart problems, including heart failure. It’s important to tell your doctor if you have heart problems, especially heart failure, before starting Humulin R. There are certain other diabetes medications that can increase your risk of heart failure when taken together with Humulin R. These medications are known as thiazolidinediones. Examples include Avandia (rosiglitazone) and Actos (pioglitazone). Your doctor will recommend the safest plan for treating your diabetes. If they do prescribe Humulin R for you, they may have you stop taking the thiazolidinedione drug.

Kidney or liver problems. Humulin R is typically considered safe for people with liver or kidney problems. But your doctor may want to monitor your liver or kidney function closely in these cases. This is due to the fact that small changes in how these organs function can change how your body responds to Humulin R. Your doctor may need to change your dose of the drug frequently if you have liver or kidney problems.

Allergic reaction. If you’ve had an allergic reaction to Humulin R or any of its ingredients, your doctor will likely recommend that you do not take it. Ask them about other medications that may be better treatment options.

Alcohol and Humulin R

If you drink alcohol, you should talk with your doctor about how much, if any, is safe during your treatment with Humulin R.

Alcohol can affect your blood sugar level, which can cause Humulin R not to work as well. It can also increase your risk of certain side effects of Humulin R, such as:

Your doctor can go into more detail with you about the risks of drinking alcohol while being treated with Humulin R.

Pregnancy and breastfeeding with Humulin R

Humulin R is believed to be safe to use while pregnant. High blood sugar levels, which Humulin R is used to manage, increase the risk of pregnancy complications. These include loss of pregnancy and harm to the mother.

There aren’t any known safety issues with breastfeeding while being treated with Humulin R.

If you have questions or concerns about pregnancy or breastfeeding during your Humulin R treatment, talk with your doctor or pharmacist.

As with most medications, Humulin R can cause side effects. Some of these, such as hypoglycemia (low blood sugar), are more common than others. And in some cases, they can be severe. Most of Humulin R’s potential side effects are the same as those of other insulin drugs.

Before starting Humulin R, talk with your doctor. Ask them questions that help you feel comfortable about the risks and benefits of this treatment option. Some examples to help get you started are:

  • If I have side effects from Humulin R, is there a lower dose I can try?
  • Are there other ways to help me manage side effects from Humulin R?
  • How does Humulin R compare with other insulins for treating diabetes?

If you have type 2 diabetes, you can get tips for managing this condition and more by signing up for Healthline’s online newsletter. And consider joining Bezzy T2D, a supportive community of others living with the same condition.


Can Humulin R cause nerve problems as a side effect?



While unlikely, it’s possible you may experience nerve problems when you first start Humulin R treatment or if your dose is increased.

Humulin R doesn’t directly cause nerve problems. But nerve problems, including peripheral neuropathy, can occur when blood sugar levels quickly go from being too high to being managed by medications such as Humulin R. This shift in blood sugar levels can also cause eye-related side effects.

But these nerve problems or eye-related side effects usually go away on their own in a few days. And properly managing blood sugar levels over the long term reduces your risk of complications caused by diabetes. And these include long-term nerve damage and vision problems.

The Healthline Pharmacist TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.
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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.