Why medicines need a second thought with type 1

Most people with type 1 diabetes find out about medicine interactions the hard way: a number they can't explain, a few days after starting something new. This page sets out the one rule that comes before everything else, and the three ways a medicine can interfere with managing your blood sugar.

Nobody warns you

Almost every medicine you will ever take was studied mostly in people whose pancreas works. For them, a small shift in blood glucose goes unnoticed, because their body corrects it automatically. For you, it shows up on the screen.

A handful of common medicines move blood glucose, hard. The danger isn't that they are unsafe for you. It is that the prescription often arrives with no mention of it, and a week later you are fighting numbers you assume are your fault. They aren't. Knowing in advance which medicines do this turns a confusing week into an expected, planned one.

So the right way to read the rest of this section is not as a list of drugs to refuse. It is a list of drugs to expect something from — and to ask about before you start.

Before anything else: the insulin does not stop

This is the single most important idea in this whole topic. Everything else is detail by comparison.

Not when you're too sick to eat. Not when you're throwing up. Not when the number looks fine. Your body needs background insulin whether food goes in or not. Without it, ketones start building within hours and keep building.

Illness, other medicines, activity and hormones can all change how much insulin you need. Adjusting the dose is normal and expected. Stopping it entirely is not.

Three ways a medicine can get in the way

Any medicine that affects your diabetes does it in one of three ways.

1. It pushes glucose up

Steroids are the big one, but they are not the only one. While you're on a medicine like this, you are likely to need more insulin than usual, for as long as you're taking it. See medicines that raise blood sugar.

2. It pushes glucose down — or hides the fall

Of the two halves, hiding the fall is the more serious one. A low you can still feel is a low you can still treat. Some medicines lower glucose directly; others leave the number alone but quiet the warning signs your body uses to tell you a low is coming.

3. It leaves glucose alone but fools your sensor

Your body is fine. The number on the screen isn't. The risk here is that you dose insulin for a reading that was never real.

Knowing which of the three categories a new medicine falls into tells you what to watch for, and what to ask your team or pharmacist before the first dose.