Not with anything sold today. Nobody has tested it. The one fortnightly result comes from a different molecule, designed for the interval rather than stretched into it [1]. The day of the week has not been studied either, as the injection day nobody tested sets out. What follows is the evidence that exists.
The one fortnightly trial
A phase 2b trial tested bofanglutide against weekly semaglutide 1 mg. Participants were Chinese adults with type 2 diabetes. The drug was given every two weeks, or weekly.
At 24 weeks HbA1c fell 2.28 percentage points on bofanglutide 18 mg every two weeks. Weekly semaglutide fell 1.60. The treatment difference was −0.68 points, 95% CI −1.04 to −0.33. The 12 and 24 mg fortnightly doses also beat the comparator. Hypoglycemia stayed rare, with no severe episodes.
The comparator choice is a familiar pattern. Semaglutide 1 mg is the diabetes dose, not the 2.4 mg weight dose. A favorable head-to-head against the lower arm keeps turning up here. The authors list their own limits: open-label, short, Chinese participants only. Gan & Lee Pharmaceuticals funded it and makes the drug.
What people actually do with the dose
The real-world data is about dose size, not spacing. A claims study covered 20,998 adults without type 2 diabetes [2]. By the sixth tirzepatide fill, 74.2% were still under 10 mg. Escalation ran slower than in the trials. Among those persistent six months, mean weight reduction was 11.9%.
That is evidence people take less drug. It is not evidence they take it less often. A smaller weekly dose holds a steady blood level. A doubled interval lets it fall, and nothing published describes the second week. What the ladder costs is counted in the dose most people reach.
Why anybody asks the question
Two reasons, and both are legitimate. The first is money: fortnightly halves the pens. The second is tolerability, and the pooled evidence gives that a size.
Fifty-five placebo-controlled trials covered 106,395 participants [3]. Gallstones carried a risk ratio of 1.46, 95% CI 1.09 to 1.97. Reflux carried 2.19, 95% CI 1.48 to 3.25. Those are about 2 and 4 extra cases per 1,000 people.
Pancreatitis, bowel obstruction, ileus, perforation, bleeding and gastroparesis all came back null. The events that push people to stretch a dose are common and unpleasant, not dangerous. That distinction is drawn in what the side effects are.
What a buyer should do
Ask the prescriber, not the price list. Changing the interval changes the exposure. A seller has no basis to advise on it. A pen stretched over two weeks also sits outside its labeled in-use period, which is a storage question first.
If the reason is cost, the lever with evidence behind it is the dose. People reach a useful result below the rungs a price list headlines. So the figure worth comparing is what a seller charges at 5 mg, not at 15. Those comparisons sit in what a GLP-1 costs per month and how long people stay on one.