The pharmacy aisle, and medicines that fool your sensor

Nobody asks you anything when you pick a cold remedy off the shelf. This page covers the over-the-counter products that most often catch people with type 1 diabetes off guard, and the medicines that leave your blood sugar alone but make your sensor show the wrong number.

The pharmacy aisle, where nobody asks you anything

Syrups carry carbs. Cough and cold liquids are often sugar-based, and the dose is repeated every four hours, all day. Sugar-free versions exist — ask for one.

"Non-drowsy" usually means a decongestant. That is typically pseudoephedrine, which pushes glucose up, and heart rate with it. It hides inside combination products, so the box may not say "decongestant" on the front.

NSAIDs on a sick day. Ibuprofen and naproxen are on the sick-day hold list when you're dehydrated. Acetaminophen is usually the safer choice for fever — with one sensor caveat, below.

The simplest habit of all: carry the box to the counter and ask the pharmacist. It takes a minute and it is free.

Medicines that lie to your sensor

This is the third way a medicine can get in the way: your glucose is fine, but the number on the screen isn't. The examples below come from Dexcom's interference guidance.

Acetaminophen, above the maximum

On Dexcom G6 and G7, normal dosing is fine. Going past the maximum — more than about 1 g every six hours in an adult — can make the sensor read falsely high.

This is not a reason to avoid acetaminophen. At normal doses on a current sensor it is a non-issue. Older sensor generations were affected by acetaminophen at ordinary doses; newer ones are not.

Hydroxyurea

Hydroxyurea makes G6 and G7 read falsely high at any dose. Dexcom says not to use sensor readings for treatment decisions while taking it.

Every brand has its own list

Dexcom, Libre and the other sensors differ. Look up the interference list for your own sensor rather than assuming this one transfers.

The rule that covers all of it

If you feel low but the sensor says you're in range — or the reading simply doesn't match how you feel — trust the finger prick over the sensor until you know why.