Normally, if your glucose drops too low, your liver steps in and releases stored glucose to bring it back up. That’s your built-in safety net. Alcohol switches that safety net off — the liver is busy processing the alcohol and stops watching your glucose.

The more you drink, the longer this window lasts. One unit (a small glass of wine or single spirit) suppresses that safety net for roughly one hour. Eight units — a big night — can switch it off for eight hours or more, often right through the night.

The main danger is a delayed low — hours after you stop drinking, often during sleep. This is why the standard advice is to check glucose before bed, set a CGM low alarm, and make sure someone near you knows what to do.

Drinks with carbohydrates (beer, cider, cocktails) can cause glucose to rise first, then fall later. The temptation to correct the rise with insulin is where things go wrong — that insulin is still active when the delayed low hits.

How the insulin adjustment guidance works: UK diabetes education programmes including DAPHNE and BERTIE establish that significant background insulin reduction is appropriate when drinking. The explorer takes this foundation and grades the reduction according to units consumed — a clinical reasoning step, not a published protocol. No randomised trials exist for graded alcohol-specific insulin adjustment, and the practical barriers to running them are significant. The percentages shown are an educated clinical assessment; all outputs should be discussed with your diabetes care team.

For AID users, the 90-minute pre-activation window is consistent with published AID guidance (2025) — activating before drinking lets the algorithm settle at a higher target before alcohol is present. The detailed explainer covers the full decision logic behind every output.