Questions remain over the efficacy-to-safety ratio of Novo Nordisk’s acquired weight loss drug monlunabant after a Phase IIa trial.

The pharma giant announced results from the study (NCT05891834) which investigated monlunabant, a small molecule oral cannabinoid receptor 1 (CB1) inverse agonist acquired in the $1bn Inversago Pharmaceuticals buyout in August 2023.

Despite positive data, with the trial meeting its primary endpoint, there are questions about dosing to better balance the safety and efficacy ratio of the drug. To better understand this, Novo Nordisk plans to initiate a Phase IIb trial in obesity next year.

Investors were apprehensive about the announcement with the company’s stock price dropping by more than 6% after the data announcement, from $134.88 at close on 19 September to a low of $126.13 on 20 September.

The trial investigated the efficacy and safety of a once-daily 10mg, 20mg and 50mg dose of monlunabant, previously called INV-202, compared to placebo. All treatment arms achieved a statistically significant weight loss, with the 10mg cohort achieving a weight loss of 7.1kg compared to 0.7 kg on placebo. There was however limited additional weight loss seen at higher doses of monlunabant.

The most common adverse events (AEs) were gastrointestinal, with the vast majority being mild to moderate and dose-dependent. There were more mild to moderate neuropsychiatric side effects, primarily anxiety, irritability, and sleep disturbances, in the treatment arm and these were also dose-dependent. There were no serious neuropsychiatric AEs.

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Novo Nordisk executive vice-president and head of development Martin Holst Lange said: “The Phase IIa results indicate the weight-lowering potential of monlunabant and that further work is needed to determine the optimal dosing to balance safety and efficacy. Obesity is a complex disease with a significant unmet need, and as an oral small molecule having a new mechanism of action, monlunabant is one of the novel projects in our pipeline with the potential of treating obesity.”

The drug is also being investigated in a Phase IIa trial in patients with diabetic kidney disease (NCT05514548).

Novo Nordisk is best known for its glucagon-like peptide receptor agonist (GLP-1RA) semaglutide, known under the market names Wegovy for obesity and Ozempic for type 2 diabetes.