A Study of Lebrikizumab (LY3650150) in Participants With Chronic Rhinosinusitis and Nasal Polyps Treated With Intranasal Corticosteroids (CONTRAST-NP)

Inclusion Criteria: * Physician-diagnosed chronic rhinosinusitis (CRS) with bilateral nasal polyps (NP). * Prior treatment with systemic corticosteroids (SCS) within the last 2 years (or a medical contraindication or intolerance to SCS), prior surgery for NP, or both. * Endoscopic bilateral NPS score of at least 5 out of 8, with a minimum score of 2 in each nasal cavity performed at screening and baseline. * Ongoing symptoms for at least 8 weeks prior to study entry (screening), including: 1. Nasal congestion with moderate or severe symptom severity (score 2 or 3) at screening and a weekly average severity score of at least 1 (range 0 to 3) at randomization, and 2. At least one other symptom, such as partial loss of smell (hyposmia), total loss of smell (anosmia), or anterior or posterior rhinorrhea. * Have concomitant asthma must be stable in the 3 months prior to screening using permitted regular asthma treatment. * Adolescent participants ≥12 to \<18 years of age and weighing ≥40 kg at time of Visit 1. Exclusion Criteria: * Have received a dose of lebrikizumab. * Have received treatment with any rescue medication and/or have the need for surgery for NP during screening and/or run-in period. * Allergen immunotherapy (subcutaneous immunotherapy \[SCIT\]/sublingual immunotherapy \[SLIT\]) initiated within 6 months prior to screening, that is not on a stable dose (3 months prior to screening). * Has received a biologic treatment approved for use in CRSwNP, asthma, or AD, even if administered to treat a different condition, within 4 months or 5 half-lives, whichever is longer, prior to screening. * Have received treatment with any biologic or systemic immunosuppressants for inflammatory disease or autoimmune disease prior to the baseline visit: 1. B cell-depleting biologics, including rituximab, within 6 months. 2. other biologics within 5 half-lives (if known) or 8 weeks, whichever is longer. 3. Systemic immunosuppressants within 4 weeks prior to baseline. * Have had any sinus intranasal surgery (including nasal polypectomy) within 6 months prior to screening * Have had prior sino-nasal surgery or sinus surgery changing lateral wall structure of the nose making it difficult to assess endoscopic NPS * Have a presence of any of the following conditions that may impact the assessment of endpoints at screening or baseline: 1. Nasal septal deviation occluding at least one nostril. 2. Antrochoanal polyps. 3. Acute sinusitis, acute nasal infection, or acute upper respiratory infection. 4. Ongoing rhinitis medicamentosa. 5. Presence of another diagnosis associated with NP (ie, eosinophilic granulomatosis with polyangiitis, granulomatosis with polyangiitis, Young's syndrome, primary ciliary dyskinesia, cystic fibrosis). Note: for adolescents, documentation for ruling out cystic fibrosis and primary ciliary dyskinesia is required. 6. A nasal cavity tumor (malignant or benign). 7. Evidence of fungal rhinosinusitis. * Have anosmia from COVID or any reason other than CRSwNP. * Participants with forced expiratory volume in 1 second (FEV1) 50% or less (of predicted normal) at screening. * Female participant who is pregnant, breastfeeding, or is planning to become pregnant, or to breastfeed during the study.