Weekly GLP-1 doses across time zones: the log, curve and reminder

A weekly injection is tied to a day of the week, and a long flight moves the day. Take the route from Los Angeles to Tokyo. Japan Standard Time is nine hours ahead of UTC with no daylight saving, and Los Angeles is seven hours behind UTC until US daylight saving ends on the first Sunday in November, then eight. So Tokyo runs 16 hours ahead in October and 17 after. This post covers what Peptrend does with a dose log across that gap. It does not cover what you should do: which day to dose on while away is a question for the prescriber and the prescribing information.

How does the dose history look in a new time zone?

Every entry moves to local time. Peptrend stores each dose as a single moment, not as a day and a clock time, and draws dates and times with the phone’s current time zone. A dose taken on Sunday at 9:00 pm in Los Angeles in October shows on Monday at 1:00 pm once the phone is on Tokyo time. Nothing in the log has changed; the same moment is being read on a different clock.

The same goes for the Dose Log rows, the Next card and the labels along every chart. Fly home and they move back.

Does the level estimate change when you travel?

No. The In Your System curve is built from the time elapsed between each dose and now, and elapsed time is the same in every zone. A dose taken 40 hours ago is 40 hours old in Los Angeles and in Tokyo, so the curve’s shape and the current figure are identical. Only the dates under the curve shift.

That curve is a decayed milligram estimate from a published half-life, not a blood level. How much is still in your system explains the model.

When does the app say the next dose is due?

At the same moment it would have at home. The next date is your last taken dose plus the medication’s interval, counted in calendar days on the phone’s current calendar. For a weekly dose that lands on the same moment a week later, to within an hour when a daylight-saving change falls inside the week. In Tokyo, a Sunday-night Los Angeles dose comes due again on Monday afternoon local time.

That is arithmetic on the log. If you and the prescriber decide to take the next dose on Sunday night Tokyo time instead, log it when you take it and every date after it follows the new dose. Logging a late or missed dose covers how the countdown reacts.

What happens to the reminder?

It needs a look after you land. Peptrend schedules one local notification, and it stores the due time as a date and a clock time — year, month, day, hour, minute — with no time zone attached. iOS matches those numbers against the phone’s clock, so a reminder set at home for Sunday at 9:00 pm can fire at 9:00 pm on Sunday in Tokyo, which is 16 hours earlier than the moment the Next card shows.

The app sets the reminder again whenever it starts up and whenever the dose history or the interval changes. Each time, it works out the clock time from the zone the phone is in. So after landing, open the app and read the Next card. The reminder follows that card, and the card reads in local time.

Two details apply to fewer people. A schedule imported from another tracker can carry a preferred time of day; with one active, the reminder fires at that clock time on the due date, read in the current zone. And the notification is local, scheduled on the phone, with no server involved.

How do you log a dose taken abroad?

The usual way. The Add sheet’s When field shows local time, so set it to the time on the clock in front of you. The app stores the moment. A dose taken on Tuesday at 9:00 pm in Tokyo in October reads as Tuesday at 5:00 am once you are back in Los Angeles.

Daily tablets work the same way, and their countdown is in hours rather than days, which makes a zone change easier to see: the ring’s hour count is the same anywhere, while the “due at” time beside it moves.

What else shifts with the time zone?

Day boundaries for weigh-ins. The trend methods group weigh-ins by calendar day, using the phone’s current calendar each time the chart is drawn. A weigh-in near midnight can fall on the neighbouring day when you view the log from another zone, and two readings that were on separate days at home can share one abroad, where same-day readings are averaged. The effect is small and reverses on the way home, but it explains a dot that seems to have moved.

Week boundaries do not move with the zone. Weekly groupings, such as the Weekly Average method, follow the phone’s region settings, which a flight does not change.

And the weigh-ins themselves are noisier on a trip. Travel changes salt, water and meal timing, all of which move the scale for reasons that have nothing to do with tissue. Why the scale jumps overnight covers the usual causes.

What will the app not tell you?

It will not say which day to dose on abroad, whether to shift your schedule gradually or at once, or how long two doses can sit apart. The prescribing information has dosing rules, and the prescriber can apply them to a particular trip. Peptrend logs what you take and keeps the arithmetic honest across the clock change. What to log with every dose covers the other fields, and support is where to report a date that reads wrong after a flight.