Novo Nordisk's experimental weight loss pill has some concerning side effects

The logo of the Danish pharmaceutical company Novo Nordisk on the facade of the new German headquarters. - Image: picture alliance / Contributor (Getty Images)
The logo of the Danish pharmaceutical company Novo Nordisk on the facade of the new German headquarters. - Image: picture alliance / Contributor (Getty Images)

Ozempic maker Novo Nordisk (NVO) announced mixed results today for a phase 2 trial of an experimental weight loss pill that works differently than its already-popular weight loss drug Wegovy.

Novo Nordisk stock fell nearly 6% during Friday morning trading after it posted the results.

The Danish pharma giant tested monlunabant, a drug it acquired in 2023 with its $1 billion purchase of Inversago Pharma, in a phase 2 trial involving 243 participants with obesity and other related health complications.

Monlunabant works by blocking CB1 receptors, which are found in the brain and nervous system and have an effect on appetite. Conversely, Wegovy works by mimicking a gut hormone that regulates blood sugar levels and reduces appetite.

The new drug was tested in once-daily doses of 10mg, 20mg, and 50mg.

Starting from an average weight of 110.1 kg (242.7 lbs), participants taking any dose of monlunabant lost significantly more weight than those on a placebo. After 16 weeks, people taking a daily 10 mg dose of monlunabant lost an average of 7.1 kg (15.6 lbs), or about 6% of their weight, while the placebo group only lost about 0.7 kg (1.5 lbs). Higher doses didn’t result in much more weight loss beyond that.

In the trial, the most common side effects were digestive issues, which were generally mild to moderate and depended on the dose. People taking monlunabant also reported more mild-to-moderate mood-related side effects, including anxiety, irritability, and sleep problems, compared to those on a placebo. However, Novo Nordisk reported no severe neuropsychiatric side effects.

“The phase 2a results indicate the weight-lowering potential of monlunabant and that further work is needed to determine the optimal dosing to balance safety and efficacy,” said Martin Holst Lange, executive vice president and head of development at Novo Nordisk, in a statement. “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.”

Novo Nordisk said it is plans to start a larger phase 2 trial of the drug in 2025.

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