Study terminated due to enrolment challenges.

The purpose of this study is to find out the effect of Lu AG06466 on the body in participants with fibromyalgia by assessing pain levels, brain signal changes, and psychiatric (mental) assessments.

This study will include 2 treatment periods and will utilize a crossover study design with a 7- to 14-day washout period between each 22-day treatment period.

Inclusion Criteria:

• The participant has a body mass index (BMI) of ≥18.5 and ≤38.0 kilograms (kg)/square meter (m^2).
• The participant has a fibromyalgia diagnosis, with self-reported pain visual analogue scale (VAS) score >4, based on a self-reported pain diary assessed for a minimum of 4 out of 7 days prior to the Baseline Visit.
• The participant is, in the opinion of the investigator, eligible based on medical history, a physical examination, a neurological examination, vital signs (including orthostatic vital signs), an electrocardiogram (ECG), and the results of the clinical chemistry, hematology, urinalysis, serology, and other laboratory tests.

Exclusion Criteria:

• The participant has a disease, including clinically significant liver disease of any origin, or takes medication that could, in the investigator's opinion, interfere with the assessments of safety, tolerability, or efficacy, or interfere with the conduct or interpretation of the study.
• The participant has any other disorder for which the treatment takes priority over the treatment of fibromyalgia in this study or is likely to interfere with the study treatment or impair treatment compliance.

Other inclusion and exclusion criteria may apply.