Insulin therapy is a life-saving and life-improving treatment for people with both type 1 and type 2 diabetes. But it has its own share of challenges like missing a dose of insulin.

Forgetting an insulin injection actually happens to every diabetic and much more frequently than you’d think. Diabetes management requires constant attention, precise calculation, and a tight injection schedule. We’re all human and can easily lose track, get distracted by our busy lives, or simply oversleep!

A missed insulin dose can cause a real headache as to what you should do. The steps to take are different whether what you’ve missed is your basal insulin injection or your mealtime insulin bolus.

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Related article: What To Do If You Run Out of Insulin?

1. What Happens if you Miss a Dose of Long-acting Insulin? 

Long-acting insulin is usually prescribed for the treatment of people with type 1 diabetes and in some cases for people with type 2 diabetes. Most of the time, it's administered once a day in the evening or the morning.

Missing a dose of long-acting insulin may have serious effects on your blood sugar levels.

What is long-acting insulin?

Long-acting insulin, also called basal insulin or background insulin, is a type of insulin that acts throughout the day to keep your glucose levels steady.

As opposed to rapid insulin that works on your meals' sugar intakes, long-acting insulin gives you a slow and constant release of insulin to lower the glucose produced by your body in-between meals and overnight.

The most common basal long-acting insulins are Lantus, Basaglar, and Levemir. They take about 2 hours to start being effective and their effects last for 24 hours.

In some cases, you may have been prescribed intermediate-acting insulin like Humulin N or Novolin N which start working one hour after being injected and have a peak effect in 4-12 hours. Ultra-long-acting insulins like Tresiba or Toujeo can even last for up to 35 hours.

Related articleA Beginner's Guide to Basal and Bolus Insulins. 

Missed basal insulin dose symptoms and consequences

Forgetting a shot of long-acting insulin can cause hyperglycemia and ketoacidosis in the worst cases.

When your body lacks insulin to use glucose, it starts burning fat for energy instead. This process produces ketones (blood acids) which are poisonous to the body. When the ketone level is too high, you risk Diabetic Ketoacidosis (DKA). It’s a very serious diabetes complication that requires immediate medical attention.

DKA mostly happens in people with type 1 diabetes, but it can also affect people with type 2 diabetes.

Apart from unusually high blood sugar levels and ketones in your urine, here are the most common symptoms when your body lacks insulin: 

  • Thirst
  • Excessive urination
  • Confusion
  • Drowsiness
  • Sleepiness
  • Tiredness
  • Fruity smell in your breath
  • Nausea
  • Loss of appetite
  • Dry skin
  • Fast heart rate 

Whether you have missed a dose of insulin or not, if you experience any of these symptoms, or if your glucose or ketone levels are high even in the absence of symptoms, immediately call your doctor or seek medical care from the nearest clinic.

Related article: How to Mix Two Insulins in the Same Syringe?

What to do if you forgot to take your basal insulin?

First, don’t panic. Missing an insulin injection happens to every diabetic occasionally! Stress can only make things worst and increase your sugar levels. Keep calm and remember that as long as you act on it, you will be fine. Here’s what you should do if you forgot your last injection of fast-acting insulin. 

Related article: A Step-by-step Guide to Using Insulin Pens for Injections!

Ask for your doctor’s advice

What to do in case you've forgotten to take your basal insulin is a scenario you should have discussed with your healthcare provider beforehand. If that situation worries you, you should anticipate and ask for your doctor’s advice long before it happens.

Diabetes is an autoimmune disease that affects every person differently. Insulin therapy and diabetes management vary considerably depending on the patient. Your doctor or endocrinologist is the best person to tell you precisely how to react in case you missed an insulin injection.

Related articleDoes Insulin Really Need to be Refrigerated?

Should you take an insulin dose?

It depends. Whether you’re using Lantus, Basaglar, Levimir, or other long-acting insulins, injecting a double dose of basal insulin can be dangerous and lead to a severe hypoglycemia.

Only inject long-acting insulin if you're absolutely sure you’ve forgotten your morning or evening injection.

If you’re sure you’ve missed a dose of long-acting insulin and you realize it soon enough (within 2 hours of your normal schedule), it’s fine to inject your usual dose. Simply be aware that your basal insulin will be active until 2 hours later in the day, so its effects will overlap with the effects of your next dose. It could increase the risks of low blood sugar, so keep a close eye on your blood sugar levels during that overlap time.

If more than 2 hours have passed since you should have injected your basal insulin, things are a bit more complicated. In that case, you should call your diabetes doctor. Indeed, calculating the remaining dose that you should take then isn’t that simple as you risk overlapping too much with your next day’s injection, which could cause severe hypoglycemia.

In any case, if you’ve missed your long-acting insulin shot or have delayed it, you must take some extra precautions within the next 24 hours. You must carefully monitor your blood glucose levels and test for ketones.

When you can’t remember if you took your insulin

If you aren’t sure whether you have taken your basal insulin this morning or yesterday evening, do not take a new dose.

As said above, injecting twice your usual dose of insulin is dangerous and can lead to severely low blood sugar levels causing life-threatening hypoglycemic coma and requiring urgent medical care.

If you can’t remember whether you’ve had your last basal insulin injection or not, call your doctor and ask for advice.

Meanwhile, monitor your blood sugar levels and test for ketones.

Monitor your blood sugar levels

In any of the above cases, you must keep a close eye on your blood sugar levels. Missing a dose of long-acting insulin or taking it later than usual will most probably have an impact on your blood glucose within the next 24 hours.

Here’s what can happen:

  • You may experience unusually high levels of blood glucose caused by a lack of insulin if you have not taken your dose of insulin or if you’ve taken a reduced dose.
  • You may have DKA (diabetic ketoacidosis) in the worst cases.
  • Your blood sugar levels may drop and cause hypoglycemia if the last hours of effects of your basal insulin overlap with the first hours of your next day's injection.
  • You may have severe hypoglycemia (dangerously low blood sugar) if you've had a second dose when you thought you've forgotten the first one.

During the next 24 hours at least, you will need to monitor your blood sugars more frequently than usual. Overnight, you should set up an alarm to wake you up every 3 hours so you can check your blood glucose. 

Immediately report any concerning numbers to your doctor.

Test for ketones

Ketones are acidic chemicals your body produces when it lacks insulin to use glucose and burns fat to produce energy instead. Lack of insulin can lead to high levels of ketones, which is dangerous and must be addressed immediately.

Your doctor or endocrinologist should have provided you with an action plan in case you’re experiencing unusually high blood sugar levels. 

Most diabetic patients are advised to test for ketones when their blood glucose is over 200mg/dL (11 mmol/L), or when they feel any of the ketoacidosis symptoms mentioned above. You can do that with urine ketone testing kits you get from the pharmacy. If your ketones results are:

  • Below 0.6 mmol/L: you’re fine. It’s a normal reading.
  • Between 0.6 and 1.5 mmol/L: test again after 2 hours.
  • Between 1.6 and 2.9 mmol/L: you must call your doctor immediately. You’re at an increased risk of DKA.
  • Above 3mmol/L: get urgent medical care. You’re at a very high risk of DKA.

When your ketones are above 0.6 mmol/L, your doctor will guide you on the steps to take and how much rapid insulin you will need to inject.

Related article: How Long Can a Diabetic Go Without Insulin?

2. What Happens if you Miss a Dose of Fast-acting Insulin?

Missing a bolus of fast-acting insulin during a meal is a totally different situation that brings its own challenges and answers. 

What is fast-acting insulin?

Fast-acting insulin, also called rapid-acting insulin, mealtime insulin, or bolus insulin is another type of insulin. It is absorbed quickly and starts acting within minutes to lower the glucose level from the sugars and carbohydrates you’ve had during a meal.

Rapid insulin mimics the surge of insulin produced by the pancreas in response to food intake.

There are two types of bolus insulins: rapid-acting insulins and short-acting insulins. The difference between the two is mostly about the time it takes for them to start working. 

Rapid-acting insulins start being efficient within approximately 15 minutes after the injection and last for two to four hours. Common brands are Humalog, Admelog, Novolog, Fiasp, and Apidra.   

Short-acting insulins, also called regular insulins start working within 30 minutes and their effects generally last for three to six hours. Common brands are Humulin R, Novolin R, ReliOn, and Velosulin BR.

Rapid insulin is mostly prescribed to type 1 diabetics, although some people with people with type 2 diabetes might also need it. Most of the time, it’s used with long-acting insulin.

Missed bolus insulin symptoms and consequences

Missing an injection of fast-acting insulin during a meal is quite a frequent situation among diabetics and it can happen to anyone.

The most common symptoms you may experience after forgetting to bolus for your meal are symptoms of hyperglycemia (high blood sugar):

  • Excessive urination
  • Increased thirst
  • Blurred vision
  • Fatigue
  • Headache

If left untreated, hyperglycemia can lead to high levels of ketones and cause diabetic ketoacidosis (see above). The symptoms and their gravity increase, and you may suffer from nausea, vomiting, dry mouth, shortness of breath, confusion, abdominal pain, and in the worst cases coma.

Whether caused by a missed insulin injection, a miscalculation of dosage, or anything else, after-meal blood sugar levels must be taken seriously, and any high numbers must be treated as soon as possible. 

Related articleHow to Calculate Your Insulin Dose?

What to do if you forgot your meal-time bolus insulin? 

Forgetting a meal-time fast-acting insulin injection is more common than you would think. Many situations may occur and distract you during lunch or dinner at a restaurant for example or make you forget your insulin at home.  

If you forgot to take your fast insulin and realize it within 2 hours after your meal, you can generally correct and inject your dose. Your blood sugar level should lower and get back to normal soon.

If you realize you’ve missed your bolus more than 2 hours after the meal, it might be more complicated. What you should do in that case depends on your current glucose levels, whether you have another meal coming soon, or if you’re about to go to bed for example. If you’re unsure what to do, call your doctor and ask for advice.

In any case, make sure to keep a close watch on your blood glucose levels during the next few hours. Monitor your blood sugars more often than usual, test for ketones, and immediately take action if your levels don’t go down or if you suffer from diabetic ketoacidosis symptoms (see above).

Missing a dose of insulin is a stressful situation for people living with insulin-dependent diabetes. But don’t panic. Taking the right steps and asking for your doctor’s advice often put you right back on track! 

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August 01, 2022


4AllFamily Customer Care Team said:

Hi David,
Thanks for your remark. The answer would vary greatly depending on each individual. As a rule of thumbs, if you’ve missed a dose of long-acting insulin and won’t have it until the next day, the best would be to limit carbohydrate intakes. But again, it depends on the individual and that’s something that should be discussed with your diabetes management team.
Best regards,

David Gay said:

It doesn’t say what to do about type of food to eat and how much if you have missed your on long acting insulin dose at better and have forgotten until its too late

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The information presented in this article and its comment section is for informational purposes only and is not intended as a replacement for professional medical advice. Always consult with a qualified healthcare provider for any medical concerns or questions you may have.