Shifts, energy drinks, pregnancy and the cup you're offered

When you work nights or rotating shifts. The cut-off still applies, but it's six hours before whenever you sleep, not before eleven. Caffeine early in a night shift and none in the second half is the arrangement that fits the evidence. Shift work damages sleep on its own, and if you're struggling, that's a conversation with a GP or an occupational health service, not a matter of coffee alone.

When it's energy drinks. The NHS figure is about eighty milligrams in a small can, and larger cans hold more. They're usually cold, sweet and drunk fast, so they're easy to have several of without noticing. Count them, apply the cut-off, and taper them like anything else. The European Food Safety Authority found no safety figure could be set for children and teenagers, so they aren't for them.

When you're pregnant or breastfeeding. The NHS says no more than two hundred milligrams a day, and the EFSA review says the same. That's a medical limit, not a suggestion, and it takes precedence over any destination you'd have chosen from chapter 18.

When you have a heart condition, high blood pressure, anxiety, or a medicine that interacts. Follow what you've been told. If nobody has told you anything and you're unsure, ask a pharmacist. If caffeine gives you palpitations, a GP should know.

When you're tired despite the taper. If a month at a low level with an early cut-off leaves you as tired as ever, the coffee wasn't the cause, and you should see a GP. Loud snoring with pauses in breathing, tiredness that doesn't lift with sleep, or tiredness with low mood or weight change all need looking at. The coffee may have been hiding it.

When you're driving tired. Have the coffee. A single cup before a long drive when you're tired is the right use of caffeine. Better still, don't drive tired, and if you're sleepy at the wheel, stop. Coffee reduces sleepiness for a while. It doesn't make a tired driver safe.

When you're offered a cup. People offer coffee as a kindness, all day, and after the cut-off you'll need a sentence. "I'd love a decaf, or a tea if not" is one, and needs no explanation. If there's no decaf, a glass of water is a complete answer.

When the office runs on it. Some workplaces have a coffee culture that's hard to stand outside. You don't have to stand outside it. Have the morning ones with everyone else. Have a decaf at three. Nobody can tell what's in the mug.

When you're on holiday or it's a special occasion. An espresso after dinner in a restaurant on holiday is a pleasure, and if you're happy to pay for it with a lighter night, that's a fair trade made knowingly. What makes it the habit is having it every night without noticing the bill.

When it's a deadline week. A stretch of late nights on a big piece of work is the one time the habit looks like sense, and for a few days it can be, if you decide it. Have the afternoon cup, know what it costs, and stop when the deadline passes. What turns it into the habit is the week after, when the deadline has gone and the three o'clock cup hasn't.

When your partner keeps making you one. Some households run on the offered cup, and the person who makes it means well. Tell them once. "I'm not having caffeine after two, so make mine a decaf, and I'll keep some in." Most people are glad to know, and it's a good deal easier than refusing a mug already in front of you.

When you slip. You'll have a bad afternoon and reach for the real thing, or a late cup at a friend's. You'll sleep worse and feel it in the morning. That's information, not failure. Go back to the cut-off the next day. There's no need to start the taper again, because one cup doesn't undo three weeks of adaptation.