Most Common Humalog Side Effects

Published August 6th, 2020 by Chris Riley
Fact Checked by
Bridget Reed
Medically Reviewed:
Camille Freking
Updated Date: Jul 7th, 2021

More than 10 percent of the population of the United States is currently living with diabetes. According to the American Diabetes Association, 34.2 million Americans had diabetes in 2018. Including the 88 million Americans over the age of 18 that have prediabetes, close to one-third of the entire population of the country has some form of diabetes. Diabetes is a condition in which the body cannot transport blood sugar in the form of glucose to cells in order to be converted into energy. This is due to the impaired ability of diabetic patients to produce insulin, the hormone that is responsible for transporting glucose to cells. In type 1 diabetes, the pancreas cannot produce insulin at all, and in type 2 diabetes that accounts for about 90 percent of all diabetes cases, the pancreas makes too little insulin. 

Why is the number of people that have this condition so large? Lifestyle factors and societal habits play a factor in the development of diabetes, but genetic factors also play a major role in whether a person is likely to develop the disease. Diabetes does not have a cure, so being diagnosed with this condition means adopting an altered lifestyle that includes both diet and lifestyle changes, as well as introducing certain medications that will likely be life-long. Keeping up a treatment regimen that includes these factors can allow diabetic patients to lead mostly normal lives and reduce the risk of other serious health consequences that can happen if the condition is left untreated. Diabetes that is not managed well can lead to a heart attack, stroke, nerve damage, retinal damage, kidney damage, and other health complications. Therefore, taking the required medication is an essential part of managing diabetes to keep additional health risks low.  

Since diabetes is a result of impaired insulin production in the body, one of the major medications used for its treatment is synthetic insulin. There are several types of insulin that are prescribed for the conditions that are classified by their duration of effect, time to peak concentration, and how quickly they act once administered. How the insulin is administered is also another factor that affects the type of insulin that is prescribed. Based on these criteria, insulin can be long-acting, intermediate-acting, or rapid-acting. Long-acting and intermediate-acting insulin are usually taken overnight, while rapid-acting insulin is used to control blood glucose spikes after eating a meal or snack. The first rapid-acting insulin to be developed that is widely prescribed for type 1 and type 2 diabetes is Humalog

What is Humalog

So now let’s discuss, what is Humalog? Humalog is marketed by Eli Lilly and is also known as insulin lispro. It was FDA-approved in 1996 and contains a version of human insulin in which the biological structure is slightly modified, so it is an ‘insulin analog..’ The natural structure of human insulin has two polypeptide chains linked together. Normally, the last two amino acids of one of the chains end with a lysine and proline. In Humalog insulin, these two amino acids are switched, giving it more favorable characteristics, such as increased absorption into the bloodstream, that make it act more rapidly compared to regular insulin. Humalog starts working 10 to 15 minutes after being administered into the body and reaches a peak concentration after one hour. It continues to work for about two to three hours. This makes Humalog ideal for processing blood sugar that quickly increases after eating food. 

How to take Humalog

The mode of administration of Humalog is through a subcutaneous injection under the skin. The manufacturer instructions recommend taking Humalog 15 minutes before you start eating to allow it to start working as soon as you start eating food. If this is not possible, you can also take Humalog as soon as you finish eating. Humalog is available as 3mL or 10 mL vials, or in a cartridge or prefilled insulin pen formulations. Humalog insulin is safe for adults and children above the age of three years with type 1 or type 2 diabetes.

Side effects of Humalog 

It is important to know what side effects Humalog can cause. Knowing the side effects of Humalog vs Novolog is vital for diabetic patients since they are both very prevalent medications for diabetes. Knowing what to expect can help you take the drug as recommended, and discuss ways to lower the chance of experiencing side effects with your doctor can help you adjust to the medication. 

Serious Side effects

The most commonly reported side effect that can occur with Humalog is hypoglycemia, or low blood sugar. This can happen if too much insulin is taken. Severe hypoglycemia can be dangerous and you should be aware of any warning symptoms of it that include headache, hunger, sweating, irritability, dizziness, fast heart rate, and feeling anxious or shaky. Carrying around glucose tablets or candy is a good idea if hypoglycemia is something that might affect you while taking insulin. Regular blood tests that measure HbA1C (A1C) will help monitor your blood sugar level over the past 2 to 3 months. These tests are done regularly for diabetic patients on insulin and can help adjust the amount and types of insulin that are included in your treatment regimen. Contact your doctor immediately if you experience hypoglycemia after taking Humalog. 

An insulin allergy or sensitivity to insulin is another possible effect of taking insulin. Humalog can be injected in the upper arms, buttocks, thighs or stomach. Hypersensitivity at the injection site may occur and can appear as swelling or redness around the injection site. Switching the injection site on a rotating basis every time you inject insulin can help reduce the occurrence of an adverse reaction at the injection site. Most minor reactions resolve in a few days to a few weeks, but more serious local reactions can occur. A whole-body allergic reaction can also occur with Humalog. Signs of a serious whole-body reaction include itchy skin rash over the entire body, trouble breathing, fast heartbeats, feeling like you might faint, or swelling in your tongue or throat. If you experience any signs of an allergic reaction to insulin, get emergency medical help immediately. 

Other common side effects that are reported by the manufacturer of Humalog are:

  • Low potassium blood levels
  • Weight gain,
  • Swelling in hands and feet,
  • Itching

Let your doctor know if you have ever had low potassium levels in your blood (hypokalemia), liver disease, or kidney disease as these could make you more susceptible to serious side effects.  

Additional common side effects that do not usually require immediate medical attention and may subside once your body gets adjusted to the medication include:

  • Body aches or pain
  • Congestion
  • Runny nose
  • Sneezing 
  • Sore throat
  • Stuffy nose 
  • Tender, swollen glands in neck
  • Unusual tiredness or weakness
  • Voice changes

Other potentially serious side effects that have been reported and must be reported to your doctor immediately are: 

  • Anxious or nervous feeling
  • Behavior change similar to being drunk
  • Blurred vision
  • Chills
  • Cold sweats
  • Confusion or difficulty thinking
  • Depression
  • Dizziness or lightheadedness
  • Drowsiness
  • Excessive hunger
  • Fast heartbeat
  • Fever
  • Headache
  • Irritability or abnormal behavior
  • Lower back or side pain
  • Nightmares
  • Painful or difficult urination
  • Restless sleep
  • Seizures
  • Shakiness
  • Slurred speech
  • Tingling in the hands, feet, lips, or tongue

Less common:

  • Dry, red or hot irritated skin 


  • Depression of the skin at the injection site
  • Dryness of the mouth
  • Fast or weak pulse
  • Itching, redness, or swelling at the injection site
  • Muscle cramps or pain
  • Nausea
  • Skin rash or itching over the whole body
  • Sweating
  • Thickening of the skin at the injection site
  • Trouble breathing
  • Unusual tiredness or weakness
  • Vomiting

This is not an exhaustive list of side effects that can occur and more information can be found here

Possible Drug Interactions of Humalog

Taking other insulin drugs with Humalog could put you at higher risk for hypoglycemia. Additionally, other anti-diabetic drugs such glipizide, glyburide, repaglinide, and nateglinide can cause hypoglycemia when combined with Humalog. Corticosteroids, such as prednisone or dexamethasone, can decrease the effect of Humalog by increasing blood glucose levels. Anti-psychotics, like clozapine, and diuretics, such as hydrochlorothiazide, could cause insulin resistance. Additionally, taking beta-blockers while on insulin can mask the signs of hypoglycemia, which can be dangerous. If you are taking any of these medications, be sure to inform your doctor to prevent a serious drug interaction from occurring. Other drug interactions may also occur. Check with your doctor or pharmacist if you are currently taking any other medications. 

Never share your vial of insulin or the needles used to inject insulin with another person. Sharing needles can lead to the transmission of viruses and can be dangerous. Discard the Humalog if it appears cloudy or viscous, even if it has not expired yet. 

How to save on Humalog

Using Humalog exactly as it is prescribed for you, along with following your treatment plan that includes dietary changes and exercise, can make diabetes a manageable condition. Being aware of how your body reacts to any new medication and following up with your doctor are important steps in this process. A pharmacy discount card can help you save on the cost of purchasing Humalog. One great option is the free discount card available from USA Rx. With this card, or by using a drug coupon also available through USA Rx, you can buy Humalog at a discounted price. The card is accepted at almost all pharmacies across the nation, so sign up today to start saving. 

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