The quest for optimal blood sugar control and patients’ comfort has pushed researchers to develop different types of insulin, ranging from fast-acting to ultra-long-acting.

Most people living with insulin-dependent diabetes are prescribed two different insulins: a bolus one to cover carbohydrate intakes and a basal one that acts in-between meals and overnight.

More than 20 types of insulin are sold in the U.S., each with a different formula, purpose, and length of action. They either come as a solution (clear insulin) or a suspension (cloudy insulin). But while some insulins are normally cloudy, cloudiness may also be a sign clear insulin has gone bad.

Therefore, knowing which insulins are cloudy and which ones are clear is essential to ensure your insulin is safe for use. 

Related article: Does insulin need to be refrigerated, and how to store it properly?

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If you're a visual learner or just prefer watching over reading, we've got you covered! Take a look at our video below, same topic, different format!

Which insulin is cloudy? 

Most insulins are clear, colorless liquids, but some intermediate-acting ones are cloudy. They owe their cloudiness to added substances used as buffers (usually zinc or isophane) that make them work over a longer time.

When this type of cloudy insulin sits for a few minutes, it's normal that the white substance settles at the bottom of the vial. However, lumps or particles should not float around after you've mixed it. This could be a sign your intermediate-acting insulin has gone bad.

Related article: How to tell insulin has gone bad?

Why are some insulins cloudy?

Cloudy insulins include NPH insulins sold under the brand names Humulin-N and Novolin-N.

Neutral Protamine Hagedorn (NPH) insulin, also known as isophane insulin, is an insoluble intermediate-acting insulin preparation and one of the most widely prescribed basal insulin. Unlike bolus insulin, which covers meals and carbohydrate intakes, basal insulin provides a sustained release of insulin to cover needs between meals and overnight.

NPH insulin contains synthesized human insulin with zinc and protamine, which gives it its cloudy appearance. After the subcutaneous injection, crystals are stacked up and gradually dissolve themselves. This allows a slow insulin release over several hours (generally 12 to 24 hours).

Related article: A Beginner's Guide to Basal and Bolus Insulin. 

Intermediate and long-acting cloudy insulins

Here’s a list of common intermediate and long-acting insulins sold in the U.S and the U.K that are cloudy:

  • NPH insulin (Humulin-N and Novolin-N) are cloudy insulins
  • Insulatard insulin comes as a cloudy, white suspension
  • Humulin-I looks white and cloudy after mixing
  • Insuman basal also has a cloudy, milky appearance once mixed
  • Monotard is a cloudy, white, aqueous insulin suspension
  • Ultratard is a long-acting cloudy insulin
  • Lente and ultra-lente insulins are cloudy too

New insulins appear on the market each year, and this list may not be exhaustive. Always read the instruction paper to check if your specific insulin is supposed to be clear or cloudy.

Related article: How to Calculate Your Insulin Dose Correctly?

Premixed insulins are cloudy

Premixed insulin is a combination of short-acting insulin with an intermediate or long-acting one. It allows patients to have one injection only instead of two without having to mix insulin themselves.

Mixed insulins always look cloudy. Before injecting, you must gently roll the vial between your palms to mix the two different types of insulin evenly. There should not be any white lumps or particles inside.

Related article: How to mix two insulins in one syringe?

Which insulin is clear? 

All other insulins and types of insulin are clear liquids. In fact, if a normally clear insulin looks cloudy, it’s a sign it has gone bad.

List of clear insulins

Rapid-acting and short-acting insulins, also known as bolus insulins, mealtime insulins, or regular insulins, are clear. They include:

  • Regular insulin (marketed as Novolin-R and Humulin-R)
  • Lispro insulin (marketed as Humalog and Admelog)
  • Aspart insulin (marketed as Novolog, Novorapid, and Fiasp)
  • Glusiline insulin (marketed as Apidra)
  • Velosulin (used for insulin pumps)

Most long-acting insulins are also clear. They include:

  • Glargine insulin (marketed as Lantus, Basaglar, and Toujeo)
  • Detemir insulin (marketed as Levemir)
  • Degludec insulin (marketed as Tresiba)

Related article: How long do insulin vials last, and how many do you need per month?


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Never use clear insulin that looks cloudy!

Cloudiness in normally clear-looking insulin is a sign it has gone bad. So if you notice any change of color, cloudiness, clumps, strings, or frost inside clear insulin, immediately throw it away and get a new vial or pen from the fridge.

Factors that can cause insulin to go bad include exposure to heat, improper storage conditions, leaving insulin out of the fridge for too long, exposure to light, and others.

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Related article: What is Mounjaro and How Does it Work for Diabetes and Weight Loss?

Never use insulin if you suspect it may have spoiled or deteriorated. It won't poison you nor make you sick. Still, it can be totally or partially inefficient and lead to prolonged high blood sugar and, ultimately, diabetic ketoacidosis, a life-threatening diabetes complication. 

What insulin are you using? Is it clear or cloudy? Feel free to share your thoughts and experiences with us in the comment section below!

December 15, 2022

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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.