Injection day is one of the most-asked practical questions about these drugs, and the internet answers it confidently: take it Friday so the worst days fall on the weekend, or Monday so you are not nauseated at a social event. A systematic review went looking for the evidence behind any of that [1]. It sits beside the other question people ask constantly and answer confidently, covered in slow responders at week eight.
It did not find any. From 1,471 records, narrowed to 1,000 after deduplication and screened in two stages against predefined criteria, three studies met inclusion: the SUSTAIN 4 trial of once-weekly semaglutide, a retrospective case series on alternate-day oral dosing, and an expert panel discussion of flexible schedules. Not one of them compared different days of the week for an injectable.
What can be said without evidence from this review is narrower and comes from the dosing schedule rather than from any study. These drugs are labeled for once-weekly administration, which means the practical goal is a day you will reliably remember, since a missed or late dose is a real effect where a Tuesday-versus-Saturday difference is a hypothetical one. If nausea reliably arrives the day after your injection, moving the injection is a reasonable experiment to run with a prescriber, and the titration pattern behind that timing is described in the dose people stay on.
One methodological note belongs on a review whose finding is an absence, because an absence is only as trustworthy as the search that produced it. Alongside PubMed and Google Scholar, the authors used an AI-assisted search tool, which is an unusual choice for a systematic review and one a reader should know about. The direction of the conclusion is not really in doubt — a trial randomizing injection day would be memorable — but the screening counts should be read as approximate.
The broader point is that a lot of what circulates as practical advice about these drugs has nothing behind it, which is worth keeping in mind when a seller's onboarding material speaks with certainty about schedules, timing or what to eat. What sellers actually publish and what they leave out is the subject of sellers publishing two prices, and how many people are still taking anything a year later is in two thirds stop within a year.