Brenipatide, VK2735 and enicepatide: three GIP/GLP-1 dual agonists with new data in September 2026

This is general educational information, not medical advice and not a suggestion to obtain or use any substance. Brenipatide, VK2735 and enicepatide are investigational drugs that are approved nowhere and cannot be legally prescribed or bought. Nothing in this article is dosing, combination or sourcing guidance. Doses named below are the labels of study arms, not amounts anyone should use. The numbers come from separate studies with different designs, so they are not head-to-head comparisons.

Within a single week in September 2026, three companies published new human data on drugs that act on the same pair of gut-hormone receptors. Eli Lilly showed a poster on brenipatide at a psychiatry congress. Viking Therapeutics released results from a maintenance study of VK2735. Roche announced phase 2 results for enicepatide in type 2 diabetes. All three are dual agonists of the GIP and GLP-1 receptors, the principle behind the approved drug tirzepatide. They share a mechanism, but the three studies asked very different questions, and that is the thread of this article. For a general introduction to the class, see our overview of GIP/GLP-1 dual agonists.

Why GIP is the common thread

GLP-1 and GIP are two hormones the gut releases after a meal. Both help the pancreas release insulin when blood sugar rises. GLP-1 also slows stomach emptying and acts on appetite centres in the brain, and drugs such as semaglutide are built on it alone. GIP was long considered the less useful partner. Tirzepatide changed that view by activating both receptors in one molecule.

Lilly's poster adds a detail that matters for this story. It states that GIP and GLP-1 receptors occur well beyond the pancreas: in the gut, heart, lungs, kidneys, liver, fat tissue and brain. That wide distribution is the stated reason why receptor agonists of this kind might be studied for conditions far from metabolism. Whether that reasoning holds up in patients is still an open question.

The three molecules also differ from each other. Roche describes enicepatide as signalling-biased, meaning it is designed to favour one intracellular signal over receptor internalisation. Our earlier article on enicepatide explains that design. A full chemical structure for either molecule could not be found in Lilly's or Viking's publications. The author of the newsletter The Incretin Space has put forward two hypotheses based on patent and structure research. The first is that brenipatide resembles retatrutide with its glucagon-receptor component removed. The second is that VK2735 may share the amino-acid chain of tirzepatide but carry a fatty-acid side chain ending in a phosphonate group. Neither hypothesis could be confirmed in company publications, so both remain speculation.

Brenipatide: a dual agonist that is not being developed for weight

Clinical data on brenipatide, coded LY3537031, were presented as poster P-175 at Psych Congress 2026 in New Orleans, held from 15 to 19 September. The venue is unusual for a GIP/GLP-1 drug. The poster's stated objective was to find a dosing regimen for substance use, psychiatric and immunologic disorders, not for obesity or diabetes.

The study. NCT06606106 is a phase 1 multiple ascending dose study, blinded for investigators and participants, with an 8-week follow-up. Part A enrolled people with a BMI between 27 and 45. Part B enrolled people with a BMI between 22 and 26.9. Part C enrolled people of Japanese or Chinese ethnicity in the same lower BMI range. According to the poster's tables, 184 people received brenipatide and 28 received placebo. Five dose levels were tested with weekly injections until day 78, and the highest level was given only in Part A. The poster presents interim data from completed cohorts.

Body weight. Lilly used body weight change as a surrogate marker to confirm that the drug was pharmacologically active across doses. According to the poster, the change in weight grew with the dose. The results appear only as a chart without printed numbers, so this article gives no figures. The chart also shows weight rising again in all groups after dosing ended. Secondary sources have read values off the curves, but we leave those out because Lilly has not published them.

Pharmacokinetics. The poster reports a mean half-life of 9.08 to 12.5 days and peak-to-trough ratios between 1.35 and 1.59. A ratio close to 1 means blood levels barely fluctuate between two weekly injections. Exposure rose in proportion to dose and looked similar across ethnic groups. The poster gives no value for Tmax, the time to peak concentration after an injection.

Tolerability. No serious adverse events or deaths were reported. Four participants on brenipatide, or 2.2%, stopped treatment because of an adverse event. Gastrointestinal adverse events occurred in 25% of participants in both the brenipatide and the placebo groups. Nausea, vomiting and diarrhoea were mild except for two moderate episodes of nausea, and none of them led to discontinuation. One finding stands out. Dysaesthesia, an abnormal skin sensation such as burning or tingling, was reported by 15.2% of people on brenipatide and by nobody on placebo. All cases were mild except one moderate case, all resolved, and one led to discontinuation. The study was small and mostly male, so these rates are provisional.

The trial programme. A search of ClinicalTrials.gov on 26 September 2026 finds twelve phase 2 or phase 3 studies of brenipatide. Four phase 3 studies cover alcohol use disorder and major depression. Four of the eight phase 2 studies cover bipolar disorder, schizophrenia, opioid use disorder and relapse after quitting smoking. The other four cover irritable bowel syndrome with constipation or with diarrhoea, asthma and chronic obstructive pulmonary disease (COPD). This list is a registry finding and says only what is being tested. No efficacy results for any of these conditions could be found.

VK2735: what the maintenance study tested

VK2735 from Viking Therapeutics is already in phase 3 for obesity. VANQUISH-1 (NCT07104500) enrolled people with obesity, and VANQUISH-2 (NCT07104383) enrolled people with obesity and type 2 diabetes. According to Viking's presentation, both are fully enrolled, and results are expected in the second half of 2027. The data released on 22 September 2026 come from a different study, VK2735-102, which asked a narrower question. How much of the weight lost can be kept when injections become less frequent?

Design. According to Viking, about 180 adults with a BMI of at least 30 and no other major illness took part. In the induction phase, all active groups received 21 weekly injections, with the dose raised step by step. In the maintenance phase from week 21 to week 33, most participants moved to a new schedule. The options were continued weekly dosing, a lower dose every other week, a dose once a month, or placebo. A 5-week follow-up period came after that. ClinicalTrials.gov lists VK2735-102 as a double-blind, placebo-controlled phase 1 study (NCT07838740). The results released so far cover its first part, which tested injections only.

Induction. At week 21, mean body weight in the four dose groups had fallen by between 16.3% and 18.7%, against 0.1% on placebo. The largest group, the 17.5 mg arm with 118 participants, lost 17.8%. Viking's presentation counts 143 people on VK2735 who were weighed at week 21. Of these, 90% had lost at least a tenth of their body weight, compared with none on placebo. During induction, 13% of participants stopped early, and 1% stopped because of an adverse event. Nausea was reported by 42%, vomiting by 27%, diarrhoea by 20% and constipation by 11% of people on VK2735. Viking calls the titration scheme accelerated.

Continued weekly dosing. A group of 13 people stayed in the 17.5 mg arm with weekly injections until week 33. Their mean weight loss reached 21.7%, while the placebo group of 15 people ended 0.3% above baseline. Viking reports that the curve had not flattened. With only 13 people, that figure is uncertain.

Maintenance. Viking expresses the result as the share of week-21 weight loss still present at week 33. Among the every-other-week arms, the figure was 96.7% in the 10 mg arm, 89.9% in the 7.5 mg arm and 82.5% in the 5 mg arm. Among the monthly arms, it was 90.2% in the 17.5 mg arm and 85.8% in the 20 mg arm. The 22.5 mg, 15 mg and 10 mg arms followed with 84.9%, 84.1% and 82.3%. People switched from weekly injections to placebo kept 61.1%, which means they regained almost two fifths of the weight they had lost within 12 weeks. Each maintenance arm had only 10 to 16 participants, so small differences between arms carry little weight.

Gastrointestinal complaints fell sharply during maintenance. In the every-other-week arms, 5% reported nausea and 3% vomiting, against 0% and 7% on placebo. In the monthly arms, 4.5% reported nausea and 8% vomiting. Viking states that these rates were not meaningfully different from placebo. Part of this decline is expected, because people who tolerated induction poorly had already dropped out before week 21.

Enicepatide: the type 2 diabetes readout

Enicepatide, formerly CT-388, came to Roche with the acquisition of Carmot Therapeutics. In January 2026, Roche reported results from the obesity trial NCT06525935 in people without diabetes. At 48 weeks, the highest tested dose led to a placebo-adjusted weight loss of 22.5% by the efficacy estimand, or 18.3% by the treatment-regimen estimand. Two phase 3 trials in obesity, ENITH-1 (NCT07351045) and ENITH-2 (NCT07351058), are now recruiting.

The new trial. On 22 September 2026, Roche published an ad hoc announcement on CT-388-104 (NCT06628362). The randomised, double-blind, placebo-controlled phase 2 trial ran for 48 weeks in 447 adults with type 2 diabetes and overweight or obesity. According to Roche, it met both primary endpoints, with dose-dependent reductions in blood sugar and body weight.

The numbers. Roche published efficacy figures only for the highest tested dose, the 24 mg arm. HbA1c fell by 2.65 percentage points from a mean baseline of 8.1%. In participants who started above 8.5%, it fell by 4.13 points. At week 48, 90% of that arm had an HbA1c of 6.5% or less, and 62% were below 5.7%, the range considered normal. Mean weight loss was 15.5%, and according to Roche it had not yet levelled off. Across all enicepatide arms, 2.0% of people stopped treatment because of adverse events, against nobody on placebo. Gastrointestinal effects were the most common adverse events and mostly mild to moderate.

What the release leaves open. It does not say whether the 15.5% and the 2.65 points are placebo-adjusted, nor which estimand was used. Placebo results and figures for the lower doses are missing. Weight loss in people with type 2 diabetes is usually smaller than in people without diabetes, a pattern documented for tirzepatide as well. For that reason, the 15.5% cannot be set directly against the 22.5% from the obesity trial. Roche plans to start a phase 3 programme in blood-sugar control and cardiovascular outcome trials in the first half of 2027.

Half-life, Tmax and tolerability — what the pharmacokinetics suggest

Two pharmacokinetic values shape how a weekly injection behaves. The half-life is the time it takes for half of the drug to leave the body. Tmax is the time from injection to the highest blood level. A long half-life with a late Tmax gives flatter blood levels, while a short Tmax produces a sharper peak after each injection. Whether flatter levels mean fewer gastrointestinal complaints is a hypothesis that several companies cite. It has not been tested in a direct comparison.

• Tirzepatide. According to the US prescribing information, the half-life is about 5 days, and peak levels are reached 8 to 72 hours after injection.
• Brenipatide. The poster reports a mean half-life of 9.08 to 12.5 days. No Tmax figure could be found.
• VK2735. Viking's 2023 phase 1 announcement gives a half-life of about 170 to 250 hours after single doses, roughly 7 to 10 days. Tmax was about 75 to 90 hours.
• Enicepatide. The published phase 1 study by Chakravarthy and colleagues reports a half-life of 123 to 139 hours after single doses. After repeated doses, it was 130 to 151 hours. That is roughly 5 to 6 days, about the same as tirzepatide. Tmax was about 24 hours at the higher doses and 72 hours at the lowest single dose.

The chart below shows the upper end of each published range. Where a source gives days, the value is converted to hours, so 12.5 days become 300 hours. The full ranges are in the list above and in the table further down.

The tolerability figures from the three studies do not line up. The 25% rate of gastrointestinal events for brenipatide was measured in a small, mostly male group, and placebo reached the same rate. During VK2735 induction, nausea and vomiting were reported considerably more often, in a study whose titration Viking calls accelerated. For enicepatide, no published rates could be found yet, only a discontinuation figure. A longer half-life might explain part of the differences, but dose, titration speed, population and study length could explain just as much.

What is and is not comparable

The table sums up what each company has published. Every entry refers to an investigational drug.

The weight results that are available as printed numbers span different populations and durations. Enicepatide's 15.5% came after 48 weeks in people with type 2 diabetes. VK2735's 17.8% and 21.7% came after 21 and 33 weeks in people with obesity but without diabetes. For brenipatide, the poster offers only a chart, not a figure, and dosing lasted until day 78, about 11 weeks.

Three things are comparable. All three molecules act on the same two receptors. All three are designed for weekly injection or longer intervals. And all three are, for now, investigational substances with no approval.

Three things are not comparable. The first is the patients: people with diabetes in one study, people with obesity in another, and people of normal weight in part of the third. The second is time: 11 weeks of dosing for brenipatide, up to 33 weeks for VK2735 and 48 weeks for enicepatide. The third is the question each study asked. Lilly looked for a dose range for non-metabolic conditions, Viking tested maintenance schedules, and Roche tested blood-sugar control. A ranking of the three molecules cannot be drawn from these data. That would require a direct comparison in the same trial, and none could be found.

In sport, the question does not arise, since none of the three is approved. Substances without any government approval for human therapeutic use fall under section S0 of the WADA Prohibited List, which applies at all times. Our overview of peptides banned in sport explains that category.

Common questions

What is brenipatide?

Brenipatide, also coded LY3537031, is an investigational dual GIP/GLP-1 receptor agonist from Eli Lilly. It is approved nowhere. Data from a phase 1 study were presented as a poster at Psych Congress 2026. Lilly describes it as being studied for substance use, psychiatric and immunologic disorders rather than for weight.

Which conditions is brenipatide registered for in clinical trials?

As of 26 September 2026, ClinicalTrials.gov lists twelve phase 2 or phase 3 studies of brenipatide. Alcohol use disorder and major depression are studied in phase 3. Bipolar disorder, schizophrenia, opioid use disorder, relapse after quitting smoking, both main forms of irritable bowel syndrome, asthma and COPD are studied in phase 2. A registry entry shows what is being tested, not that the drug works for any of these conditions.

What did the VK2735 maintenance study test?

Viking gave about 180 adults with obesity weekly VK2735 injections for 21 weeks. Most of them then moved to one of several 12-week maintenance schedules: continued weekly dosing, dosing every other week, monthly dosing, or placebo. The question was how much of the week-21 weight loss would still be there at week 33.

How much weight loss was kept when VK2735 was given less often?

According to Viking, the every-other-week arms kept between 82.5% and 96.7% of their week-21 weight loss at week 33. The monthly arms kept between 82.3% and 90.2%, against 61.1% in people switched to placebo. The arms had only 10 to 16 participants each.

What did Roche report for enicepatide in type 2 diabetes?

In the 48-week phase 2 trial CT-388-104, Roche reported results for its highest tested dose. HbA1c fell by 2.65 percentage points from a baseline of 8.1%, and mean weight loss was 15.5%. The release did not say whether these figures are placebo-adjusted and gave no numbers for the lower doses.

How do the half-lives of brenipatide, VK2735 and enicepatide compare with tirzepatide?

The US label gives tirzepatide a half-life of about 5 days. Published values are 9.08 to 12.5 days for brenipatide, roughly 7 to 10 days for VK2735 after single doses, and about 5 to 6 days for enicepatide. The figures come from different study designs, so they indicate a direction rather than an exact ranking.

Are brenipatide, VK2735 or enicepatide approved or allowed in sport?

None of the three is approved anywhere. Substances without any government approval for human therapeutic use fall under section S0 of the WADA Prohibited List, which applies at all times.

Sources

• Eli Lilly and Company, Brenipatide, a GIP/GLP-1 Receptor Agonist: Clinical Data Supporting Dose Selection for Substance Use, Psychiatric and Immunologic Disorders (poster P-175, Psych Congress 2026)
• ClinicalTrials.gov, NCT06606106: A Study of LY3537031 in Overweight, Obese, and Healthy Participants
• ClinicalTrials.gov, Registered studies with brenipatide
• Viking Therapeutics, Positive Topline Results from Maintenance Study of GLP-1/GIP Agonist VK2735 (22 September 2026)
• Viking Therapeutics, VK2735-102 Maintenance Study: Topline Results (presentation, September 2026)
• Viking Therapeutics, Results from Phase 1 Clinical Trial of Dual GLP-1/GIP Receptor Agonist VK2735 (28 March 2023)
• ClinicalTrials.gov, NCT07838740: A Phase 1 Study of VK2735 in Obese Adults Without Comorbidities (VK2735-102)
• ClinicalTrials.gov, NCT07104500: VK2735 for Weight Management Phase 3 (VANQUISH 1)
• ClinicalTrials.gov, NCT07104383: VK2735 for Weight Management Type 2 Diabetes Phase 3 (VANQUISH 2)
• Roche, Positive Phase II results for dual GLP-1/GIP receptor agonist enicepatide in people living with type 2 diabetes and overweight or obesity (22 September 2026)
• Roche, Positive Phase II results for its dual GLP-1/GIP receptor agonist CT-388 (27 January 2026)
• ClinicalTrials.gov, NCT06628362: A Study of Enicepatide (CT-388) in Participants Who Are Overweight or Obese With Type 2 Diabetes
• ClinicalTrials.gov, NCT07351045: ENITH-1
• ClinicalTrials.gov, NCT07351058: ENITH-2
• Chakravarthy et al., Molecular Metabolism 2025, Effects of CT-388, a once-weekly signaling-biased dual GLP-1/GIP receptor agonist, on weight loss and glycemic control in preclinical models and participants with obesity
• Eli Lilly and Company, Tirzepatide injection, US prescribing information
• World Anti-Doping Agency, The Prohibited List
• The Incretin Space (secondary source), Brenipatide, VK2735 and Enicepatide (24 September 2026)