Do Cold and Allergy Medications Affect Blood Sugar?

Medically reviewed by Anna Goldman, MD.

Before I came down with a nasty cold last February, it had been years since I’d been sick — not even COVID-19 felled me. So, my medicine chest and I were unprepared with over-the-counter meds when I woke up with a sore throat from post-nasal drip, a bad cough, and a stuffy nose. I dragged myself over to the neighborhood drug store to buy cough medication, cough drops, and a decongestant. But I was in no condition to deal with an aisle overflowing with every triangulation of options, and had no idea what impact any given medication would have on my blood sugar. I finally wilted under the pressure and made some random selections so I could get back home and crawl into bed.

If this has happened to you, too, the hope is that this article will clarify how to select the right medication. Ideally, you’ll do this when you’re feeling well, ahead of coming down with a cold, flu, or seasonal allergies. That way you can stock up on over-the-counter meds so should you get sick, you’re prepared to take care of yourself without also impacting your blood sugar.

Congestion

Maybe you’re stuffed up because you have a cold. Or maybe you have allergies. If you have diabetes, you might want to be wary of using any product that features or includes pseudoephedrine. 

According to the Mayo Clinic, pseudoephedrine works to open your nasal passages by constricting the blood vessels in the nose, which tend to swell with excess blood to fight infection. Pseudoephedrine is an active ingredient in nasal decongestant products including:

Sudafed
Zyrtec-D
Allegra-D

But this ingredient may cause blood glucose levels to rise, along with blood pressure and heart rate. In fact, the labels on these products specifically include diabetes in their list of conditions in which you should, “Ask a doctor before use if you have…”. 

We’re not aware of any evidence that pseudoephedrine causes serious blood sugar problems, but it might be smart to follow those directions and consult your doctor first. 

Phenylephrine is another common decongestant, usually found in multisymptom medications such as:

Advil Multi-Symptom Cold & Flu
Sudafed PE
Vicks DayQuil Cold & Flu. 

Phenylephrine, too, can increase your blood sugar levels, according to the Mayo Clinic. There’s also another good reason to question taking phenylephrine. In 2023, the FDA said it may not work!

If you have allergies, you may be tempted to take an antihistamine like chlorpheniramine or diphenhydramine, which is the active ingredient in Benadryl. While antihistamines don’t directly impact blood sugar, they can make you drowsy, which can make it more difficult to track your blood glucose levels.

A nondrowsy antihistamine might be a better option, such as:

cetirizine (Zyrtec)
desloratadine (Clarinex)
fexofenadine (Allegra)
levocetirizine (Xyzal)
loratadine (Claritin, Alavert)

Still another option for allergy sufferers is a class of drugs called intranasal steroids or corticosteroids. This includes nasal sprays like Flonase, with the active ingredient of fluticasone propionate. Though some steroid treatments can directly cause hyperglycemia, at least one study has shown that intranasal steroids have no impact on blood sugar levels in people with diabetes. 

Just be aware that some drugs combine multiple active ingredients, such as Zyrtec-D, which has both cetirizine and pseudoephedrine. Read the label and check first with your doctor if you’re concerned.

There are also nonmedical ways to ease congestion, according to the Cleveland Clinic, including:

Taking a hot shower 
Drinking hot liquids like water, tea, and, yes, chicken soup
Staying hydrated with water
Nasal irrigation using a neti pot 
Eating spicy food
Use a humidifier
Use a saline nasal spray
Open up nasal passages by applying an adhesive strip

Coughing

There are two general types of cough medicine. Cough suppressants make you cough less often. Expectorants help you remove more mucus when you cough.

The most common OTC cough suppressant uses dextromethorphan, including the following medicines and many others:

Robitussin Maximum Strength (and many other Robitussons)
Vicks Formula 44
DayQuil Cough

The most common expectorant is guaifenesin, found in Mucinex and many other brands. Dextromethorphan and guaifenesin are often used in combination; these combination drugs often have the initials DM in their names, such as Robitussin DM.

We could find no indication in the research that either of these two ingredients is harmful for people with diabetes. In fact, there is one study showing that dextromethorphan increases insulin levels and improves glucose tolerance among type 2 diabetes patients. 

Though the active ingredients may be perfectly safe, there’s a big but here, however: sugary “excipients” (inactive ingredients). Cough syrups and cough drops often include sugar for a variety of reasons.

Unfortunately, if you try to check the labels they list only the ingredient names, not amounts, making it challenging to evaluate how many carbs are in a single dose. Some sources report that a shot of NyQuil, for example, has 19 grams of carbohydrates! In many cases, you can opt instead for diabetic versions that contain artificial sweeteners. 

Fever, Aches, and Pain Relief

The final component of a nasty cold or flu can be fever, aches, or pains. Fever reducers are generally considered safe to take over the counter, but there a few troubling reports in the medical literature.

There is some evidence that nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin, ibuprofen, and naproxen are associated with bad events in people with diabetes. NSAIDs can increase insulin release from beta cells, which can lower blood sugar, but may cause hypoglycemia in people using glucose-lowering medication such as sulfonylureas. Additionally, a 2023 study found that short-term use of NSAIDs is linked to heart failure among people with type 2 diabetes. Of course, you should check with your doctor to find out if you can use it short term.

The better choice may be acetaminophen (like Tylenol) to manage fever. There’s no evidence that it affects blood sugar levels. But a 2019 study found that older patients with type 2 diabetes taking acetaminophen had three times the risk of having a stroke.

Acetaminophen has another surprising effect. American Diabetes Association states that some continuous glucose monitor sensors can be affected by acetaminophen and give false readings. The Dexcom G7, for instance, may falsely provide elevated readings if you take more than one gram of acetaminophen every six hours. On the other hand, FreeStyle Libre has found minimal impact and the manufacturer has issued no warning. Read your user manual to learn if this could be a potential issue.

Sick Day Management

Being ill with diabetes can be a frustrating and even dangerous experience because sicknesses like the flu can cause rapidly escalating blood sugar levels and increase the risk of diabetic ketoacidosis (DKA). 

If you haven’t considered how to plan for sick days in the context of having diabetes, we have some good suggestions here. Additionally, below are several takeaways to help you wrap your head around how to treat your body when you’re downed with a cold or seasonal allergies even as you’re living with diabetes:

Be prepared. Talk with your doctor at your next physical or send a note asking about what you can and cannot take in terms of over-the-counter medications, and then stock up on them before you may need them. Also have all the other supplies you may need, like a thermometer, boxes of facial tissues, adhesive breathing strips, a neti pot, a saline spray, chicken or vegetable soup, decaffeinated tea, and a humidifier. 
Read labels. Remember that many OTC medicines aren’t necessarily stand-alone formulas. A cold or allergy remedy may include a variety of active and inactive ingredients, and some may not be healthy for people with diabetes. Be sure whatever is listed is safe for you. Only select what you need. If you have a stuffy nose from an allergy you probably don’t also need a cough suppressant. If the labels are confusing, speak to a pharmacist to get clarification on what your best choice is.
Be vigilant about measuring your blood sugar. Just the bodily stress of being sick can cause your blood sugar to rise. 
Ask your doctor if you should adjust your insulin or oral medications, especially if the OTC meds could impact their effectiveness.
Make sure you have plenty of your usual diabetes supplies always on hand.

Editorial Sources & Fact-Checking