Weekly RM-718 shows double-digit BMI reduction in small hypothalamic obesity trial

Rhythm Pharmaceuticals is expanding its rare-obesity strategy beyond its approved Imcivree franchise, with preliminary RM-718 data supporting the company’s effort to offer patients a once-weekly treatment option. The experimental therapy produced an 11.6% mean reduction in body mass index after 16 weeks in seven evaluable patients with acquired hypothalamic obesity. Although the open-label dataset is too small to establish a dependable efficacy or safety profile, it gives Rhythm Pharmaceuticals an early basis for advancing a drug designed to combine meaningful weight reduction with less generalized skin hyperpigmentation. RM-718 now sits alongside daily injectable Imcivree and oral candidate bivamelagon in a three-format portfolio that could broaden the company’s commercial reach if each treatment develops a distinct clinical role.

The commercial logic extends beyond offering another weight-loss medicine. Rhythm Pharmaceuticals is attempting to create multiple treatment formats for patients with rare neuroendocrine diseases, allowing physicians to choose among a daily injection, a possible oral drug and a possible weekly injection. RM-718 could become particularly valuable if it preserves meaningful weight reduction while reducing the generalized skin hyperpigmentation associated with existing melanocortin receptor therapy.

The Phase 2 data are not mature enough to establish that advantage. Eleven patients entered the acquired hypothalamic obesity cohort, eight remained on treatment as of July 16, 2026, and only seven had reached the 16-week efficacy assessment. Two patients discontinued because of adverse events, while another withdrew during the study’s extension period.

The 11.6% BMI reduction gives RM-718 credibility but not yet a competitive profile

The seven evaluable patients experienced an average 11.6% reduction in body mass index from baseline after 16 weeks. Rhythm Pharmaceuticals said the result was broadly consistent with the 10.1% mean reduction observed with the highest tested dose of oral bivamelagon after 14 weeks and the 10.1% reduction recorded with setmelanotide after 16 weeks across earlier Phase 2 and Phase 3 studies.

Those comparisons help show that RM-718 is activating the intended biological pathway, but they do not prove that the weekly injection is equivalent or superior to the company’s other medicines. The results come from separate studies with different populations, sample sizes and designs. The RM-718 cohort also lacks a placebo group, and one unusually strong or weak response can significantly change the average in a seven-patient dataset.

The early safety observations may prove more strategically important than the headline weight result. Rhythm Pharmaceuticals reported two mild cases of hyperpigmentation, both limited to the injection site, with no generalized hyperpigmentation observed. The most common adverse events were injection-site reactions, nausea and vomiting. One participant stopped treatment because of injection-site induration, while another discontinued after experiencing nausea.

RM-718 is designed to activate the melanocortin-4 receptor while largely sparing the melanocortin-1 receptor, which is associated with skin pigmentation. That selectivity could give the treatment an advantage over Imcivree if larger and longer studies confirm that generalized skin darkening occurs less frequently without sacrificing weight reduction.

Imcivree’s prescribing information lists skin hyperpigmentation among its most common adverse reactions and recommends skin examinations before and during treatment. The approved medicine is administered as a once-daily subcutaneous injection, while RM-718 is being developed for once-weekly use.

A weekly schedule could also reduce the practical burden of chronic treatment. Patients with acquired hypothalamic obesity may require long-term therapy because the condition results from damage or dysfunction involving the hypothalamus and the biological systems that regulate hunger, energy expenditure and weight. Fewer injections could support adherence, but convenience alone will not be enough if nausea, vomiting or injection-site reactions remain common.

The preliminary findings provide enough evidence to continue developing RM-718. They do not yet show whether the drug can reproduce the 11.6% BMI reduction across a broader patient population, maintain the benefit beyond four months or deliver a clearly better safety and convenience profile than Imcivree.

Rhythm Pharmaceuticals is creating daily, oral and weekly options around one pathway

Rhythm Pharmaceuticals entered 2026 with Imcivree as its established commercial product and has since expanded the acquired hypothalamic obesity opportunity. The United States Food and Drug Administration approved setmelanotide for patients aged four years and older with the condition in March 2026. The approved maintenance regimen for most patients is a daily three-milligram subcutaneous injection following dose titration.

The launch has started strongly. Rhythm Pharmaceuticals received more than 400 patient start forms from approximately 300 prescribers between the March approval and June 30, 2026. Global Imcivree revenue reached $71.3 million during the second quarter, rising 47% from $48.5 million a year earlier and 19% sequentially. United States revenue increased 38% from the first quarter to $51 million, supported primarily by demand in acquired hypothalamic obesity and continued growth in Bardet-Biedl syndrome.

That commercial progress means RM-718 is being developed alongside a growing product rather than as a rescue program for a struggling franchise. Rhythm Pharmaceuticals can use its existing relationships with obesity specialists, treatment centers, insurers and patient organizations if RM-718 eventually reaches the market.

The company is also preparing a Phase 3 trial of bivamelagon, its daily oral melanocortin-4 receptor agonist, in acquired hypothalamic obesity by the end of 2026. The oral candidate may offer the greatest convenience, while RM-718 could appeal to patients who prefer a weekly treatment or require a peptide-based medicine. Imcivree retains the advantages of approval, established efficacy and an active commercial launch.

This portfolio creates an opportunity to segment the market according to patient needs, tolerability and physician preferences. It also raises the risk of internal competition. A successful oral product could reduce demand for both daily and weekly injections, while a highly effective weekly therapy could slow Imcivree growth.

Rhythm Pharmaceuticals will need to establish distinct roles for each drug. Imcivree could remain the proven standard for eligible patients, bivamelagon could target those prioritizing oral administration, and RM-718 could compete through weekly dosing and reduced hyperpigmentation. That strategy only works if each candidate produces a differentiated clinical profile rather than becoming an interchangeable version of the same mechanism.

RM-718 may also expand beyond acquired hypothalamic obesity. Rhythm Pharmaceuticals expects to complete enrollment during the second half of 2026 in a separate cohort evaluating the drug in Prader-Willi syndrome. Positive results across multiple rare-obesity conditions could turn the weekly treatment into a broader pipeline asset.

Growing Imcivree revenue gives Rhythm Pharmaceuticals resources to fund its pipeline

Rhythm Pharmaceuticals ended June with approximately $330.9 million in cash, cash equivalents and short-term investments. Management expects those resources to fund planned operations for at least 24 months, providing financial room to support the Imcivree launch and advance RM-718, bivamelagon and other clinical programs.

The company remains unprofitable despite accelerating product revenue. Rhythm Pharmaceuticals recorded a second-quarter net loss attributable to common shareholders of $50.4 million, compared with a $48 million loss a year earlier. Research and development expenses reached $43.4 million, while selling, general and administrative expenses climbed to $67.4 million as the company expanded its commercial operations.

Rising selling expenses are consistent with the broader Imcivree launch, although commercial growth will eventually need to outpace the cost of building the market. Rhythm Pharmaceuticals reported $131.4 million in product revenue during the first half of 2026, up from $86.2 million during the corresponding period of 2025. Its first-half net loss attributable to common shareholders widened to $107.1 million.

The company’s shares traded at approximately $105.78 late in the August 4 session, up about 2.9% from the previous closing price of $102.78. The stock reached an intraday high of $109.51 before giving back part of the gain, suggesting investors viewed the clinical and commercial updates positively while maintaining caution around the limited RM-718 dataset. That explanation is an inference from the trading pattern rather than a confirmed account of investor decisions.

Rhythm Pharmaceuticals had a market capitalization of approximately $7.2 billion during the session, indicating that investors already assign considerable value to Imcivree and the company’s broader melanocortin-4 receptor franchise. RM-718’s early result supports that valuation narrative, but a seven-patient dataset is unlikely to determine the candidate’s full commercial value.

The preliminary findings suggest RM-718 has delivered enough clinical evidence to support further development. The 11.6% BMI reduction strengthens the case for advancing the program, while the absence of generalized hyperpigmentation provides an initial indication that the drug may achieve the differentiation Rhythm Pharmaceuticals intended.

Larger studies must now establish whether the weight reduction is durable, whether the safety profile remains favorable and whether weekly dosing creates a meaningful advantage over daily Imcivree and oral bivamelagon. RM-718 could deepen Rhythm Pharmaceuticals’ rare-obesity franchise, but its eventual role will depend on evidence showing that it is more than another active drug targeting the same pathway.

Key takeaways on what RM-718 means for Rhythm Pharmaceuticals’ obesity strategy

• RM-718 produced an 11.6% mean body mass index reduction after 16 weeks in seven evaluable patients with acquired hypothalamic obesity.
• The open-label dataset remains too small to establish definitive efficacy, safety or superiority over Rhythm Pharmaceuticals’ other melanocortin-4 receptor treatments.
• Two mild cases of hyperpigmentation were limited to injection sites, supporting the drug’s intended design but not yet proving a lower long-term pigmentation risk.
• Two patients discontinued because of adverse events involving injection-site induration and nausea, making tolerability an important issue for future studies.
• RM-718 could offer a once-weekly alternative to Imcivree, which is administered as a daily subcutaneous injection.
• Rhythm Pharmaceuticals is developing three treatment formats around the same biological pathway through Imcivree, oral bivamelagon and weekly RM-718.
• Imcivree generated $71.3 million in second-quarter revenue as its acquired hypothalamic obesity launch produced more than 400 patient start forms.
• Rhythm Pharmaceuticals had approximately $330.9 million in cash and investments, which management expects to support operations for at least two years.
• The company’s stock rose about 2.9% during the August 4 session, indicating positive but measured sentiment toward the results and business update.
• Larger and longer studies must show whether RM-718 can maintain weight reduction while delivering clearer convenience or safety advantages.