Is there a best day to take GLP-1 drugs? Researchers looked for an answer

As once-weekly GLP-1 therapies become increasingly common, researchers examined whether the day patients choose to take them could influence glucose control, weight loss, side effects, or adherence.

Is There a Better Day of the Week to Administer Semaglutide or Tirzepatide? A Systematic Literature Review. Image Credit: Celso Pupo / Shutterstock

In a recent study published in the journal Medicina, a group of researchers examined whether the day of the week on which semaglutide or tirzepatide is administered affects glycemic control, weight loss, adherence, adverse events, or patient-reported outcomes in adults with type 2 diabetes mellitus (T2DM) or obesity.

Background

T2DM and obesity affect hundreds of millions all over the globe, making treatment a major health priority. Could the chosen day of the week for the weekly dose affect benefits or side effects? Injectable semaglutide, a glucagon-like peptide-1 receptor agonist (GLP-1 RA), and tirzepatide, a dual glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 receptor agonist, are administered once weekly by subcutaneous injection. The medications have relatively long half-lives, supporting sustained drug exposure between doses. However, side effects such as nausea may negatively affect treatment adherence. Patients may choose dosing days based on their routines. Yet direct evidence on whether one day is better is currently lacking, underscoring the need for further research comparing administration days and clinical outcomes.

About the study

The systematic literature review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines and used a Population, Intervention, Comparison, and Outcomes (PICO) framework. The population consisted of individuals aged 18 years or older with T2DM or obesity/overweight status. Eligible interventions involved semaglutide or tirzepatide, including subcutaneous or oral formulations, with studies examining specific days, preferences, or flexible schedules. Outcomes included glycated hemoglobin (HbA1c), fasting plasma glucose, time in range (TIR), body weight, weight loss, adherence, persistence, adverse events, and patient-reported outcomes.

Database searches were conducted through June 15, 2026, in SciSpace Deep Search, SciSpace Basic Search, SciSpace Full Text Search, Google Scholar, and PubMed. The search identified 1,471 records overall, and studies were screened in two stages using predefined PICO-based criteria, with AI-assisted scoring during abstract screening. Records scoring at least 4.0 during abstract screening advanced to full-text assessment, where a threshold of 4.5 was applied. Data were then extracted on study design, participant characteristics, timing of intervention administration, outcome measures, compliance measures, and adverse effects. Overall methodological quality was assessed using the Cochrane Risk of Bias tool (RoB 2.0), the Newcastle-Ottawa Scale (NOS), and the Appraisal of Guidelines for Research and Evaluation II (AGREE II). The review protocol was not prospectively registered, and the authors noted that the AI-assisted screening was not fully reproducible by independent reviewers because of proprietary algorithm parameters.

Study results

The search identified 1,471 records, while 380 duplicates were removed and 91 records were trimmed to reach the screening target, after which 1,000 records underwent abstract screening. Of these, 997 were excluded: 850 did not examine administration timing or day-of-week effects, 100 assessed general efficacy without temporal analysis, and 47 focused on other GLP-1 RAs. Three studies passed full-text assessment and entered qualitative synthesis. They included one randomized controlled trial (RCT), one retrospective case series, and one expert panel discussion. None was designed to compare different days for semaglutide or tirzepatide.

The SUSTAIN 4 investigation was an open-label, parallel-group, multicenter, international, phase 3a trial that lasted 30 weeks and was conducted in 1,089 patients with T2DM inadequately controlled on metformin, with or without sulfonylureas. Patients in the trial were receiving weekly subcutaneous injections of semaglutide at doses of 0.5 or 1 mg, or once-daily injections of insulin glargine. Semaglutide produced greater reductions in HbA1c and body weight than insulin glargine. For the 1.0-mg dose, the estimated treatment difference was −1.21 percentage points for HbA1c and −5.94 kg for body weight. However, patients selected their injection day based on preference, and outcomes were not analyzed by injection day. The trial established efficacy but did not answer whether a weekday was superior.

The second study was a retrospective case series of 10 adults with T2DM who used oral semaglutide 14 mg on an alternate-day regimen to minimize gastrointestinal symptoms. Data from ambulatory glucose profiles showed no statistically significant differences in TIR, time-above-range (TAR), or time-below-range (TBR) between days when the drug was taken and days when it was not. The findings suggest that semaglutide’s glucose-lowering effects may persist beyond the immediate post-dose period. Nonetheless, the small sample size, unapproved alternate-day dosing regimen, absence of a control group, and use of an alternate-day schedule limit generalizability and causal interpretation.

The third study was an expert panel discussion on flexible oral semaglutide timing in Italian practice. Based on expert opinion and limited observational evidence, the panel considered flexible timing potentially useful for adherence without compromising glycemic control or weight loss. It emphasized individualizing schedules based on patient preferences, lifestyle, and tolerability, but no quantitative measures of adherence or satisfaction were reported. The review characterized these conclusions as hypothesis-generating expert consensus rather than evidence-based clinical recommendations.

Conclusions

The evidence did not identify an optimal day for administering semaglutide or tirzepatide in adults with T2DM or obesity, but this absence of evidence should not be interpreted as evidence that all dosing days are clinically equivalent. The three included studies did not directly compare weekdays, and no eligible study examined the timing of tirzepatide administration. Limited indirect evidence and expert opinion suggest that flexible schedules tailored to individual preferences and lifestyles may support adherence and tolerability without compromising glycemic control or weight loss. Clinicians should use shared decision-making when selecting an administration day and emphasize consistency in weekly dosing.