MBX Biosciences Inc. (MBX): Framing expectations and stock implications for MBX-4291 ahead of 12-week data

Research evidence excerpt

MBX Biosciences Inc. (MBX): Framing expectations and stock implications for MBX-4291 ahead of 12-week data

Goldman Sachs MBX Biosciences Inc. (MBX)

profile and visibility to a role in the obesity market (GSe: $120B global peak sales

indication), consistent with the key debate across other smid-cap obesity assets in our

coverage (e.g. GPCR).

Timeline for resolution

Ph1 12-week data for MBX-4291 are expected in 4Q26 and will be critical in assessing

whether the early signals observed at 8 weeks translate into sustained efficacy and

tolerability at initial steady-state exposure. While we anticipate these data will provide

greater clarity on the agent’s clinical profile, many questions are likely to persist

post-data, particularly with respect to tolerability over longer dosing intervals and once

steady-state exposure is achieved, and peak weight loss that can be achieved with this

agent.

Our view

n Encouraging early signals; tolerability at steady-state remains unknown. Initial

Ph1 data suggest efficacy tracking in line with peers, supported by a PK profile

enabling monthly dosing. Tolerability appears manageable at early timepoints;

however, the dataset remains limited, and key remaining questions center on

tolerability along the path to and at steady‑state exposure, formulation

considerations (peptide burden), and peak weight loss vs. competing long‑acting

assets. We expect the upcoming 12-week readout to provide initial clarity on

steady-state tolerability as exposure builds, while formulation and peak weight loss

will require longer follow-up.

n Framing potential outcomes for the 12-week data readout. We frame outcomes

vs. long-acting/monthly peers (MariTide, MET-097i, ASC-30): i) bull case:

demonstrates best-in-class efficacy with superior GI tolerability vs.