Shares of the Danish drugmaker fell about 1.5% on Monday, 10 July, following the news.
An EMA safety committee is looking at adverse events raised by the Icelandic Medicines Agency, including two cases of suicidal thoughts potentially linked to Ozempic and Saxenda, the regulator said.
One additional patient on Saxenda reported thoughts of self-injury, the agency said.
The EMA's investigation is centered around medicines that contain the active ingredients, semaglutide or liraglutide, for weight loss.
The review comes weeks after the regulator had raised a thyroid cancer safety signal over several of Novo's products that contain semaglutide, the active ingredient used in diabetes drug Ozempic and obesity treatment Wegovy, which has seen soaring demand in the United States. Saxenda contains liraglutide.
Suicidal thoughts are not currently listed as a side effect in the EU product information of these treatments.
Side effects have hobbled several previous attempts by the drug industry to develop lucrative weight-loss drugs.
Sanofi's Acomplia, which never won a US approval, was withdrawn in Europe in 2008 after being linked to suicidal thoughts.
Acomplia was designed to modify parts of the nervous system that regulate appetite. New weight-loss drugs such as Wegovy, however, regulate appetite by mimicking a gut hormone, and does not directly interfere with brain chemistry.
The EMA said on Monday it would consider whether the review should be extended to include other medicines of the same class known as GLP-1 receptor agonists.
Patient safety is a top priority and the company takes all reports about adverse events very seriously, Novo Nordisk said.
Safety data did not show any "causal association" between the suicidal or self-harming thoughts and the drugs, it added.
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