To evaluate the population pharmacokinetic characteristics of QY201 Tablets in adolescent participants with moderate to severe atopic dermatitis (AD).

Inclusion Criteria:

1. The participant and their parent/legal guardian (if applicable) shall have effective communication with the investigator, fully understand the purpose, nature, methods and potential adverse reactions of this trial, comprehend and comply with all requirements of the study, and sign the Informed Consent Form (ICF) prior to initiation of any study procedures.

2. Age ≥12 years and <18 years (calculated based on the date of ICF signature), any gender, body weight ≥40 kg.

3. Has a documented history of atopic dermatitis (AD) for at least 6 months at screening, and meets the Hanifin-Rajka diagnostic criteria at screening.

4. Meets criteria for moderate to severe AD at screening and baseline:

   Investigator's Global Assessment for Atopic Dermatitis (vIGA-AD) score ≥3 at screening and baseline; Eczema Area and Severity Index (EASI) score ≥16 at screening and baseline; Body Surface Area (BSA) affected by AD ≥10% at screening and baseline; Weekly average of daily Pruritus Numerical Rating Scale (PP-NRS) score ≥4 at baseline.

5. Within 6 months prior to screening, documented evidence of inadequate response to or intolerance of topical therapies including topical corticosteroids (TCS) and/or topical calcineurin inhibitors (TCI); or documented indication for systemic therapy (e.g., systemic corticosteroids, conventional immunosuppressants, biologics, JAK inhibitors, etc.) for disease control.

6. The participant is able and willing to regularly apply fragrance-free and inactive-ingredient-free emollients twice daily for at least 7 consecutive days prior to randomization, and continue such application throughout the study period.

7. Participants of childbearing potential (females post-menarche, males post-spermarche) must agree to and implement effective contraception from the date of ICF signature through 3 months after the last study drug administration. For female participants of childbearing potential, serum human chorionic gonadotropin (HCG) test shall be negative at screening, and the subject must not be breastfeeding.

Exclusion Criteria:

1. Receipt of the following therapies within 12 weeks prior to baseline (or 5 half-lives, whichever is longer):

   Small-molecule targeted drugs: Janus kinase (JAK) inhibitors (e.g., Ruxolitinib, Tofacitinib, Baricitinib, Upadacitinib, Abrocitinib), etc.; Macromolecular biologics: e.g., Dupilumab, Spesolimab, etc.

2. Receipt of the following systemic therapies within 4 weeks prior to baseline (or 5 half-lives, whichever is longer):

   Systemic immunosuppressants/immunomodulatory agents (e.g., systemic corticosteroids, cyclosporine, mycophenolate mofetil, interferon gamma, azathioprine, methotrexate, etc.); Phototherapy (e.g., ultraviolet B [UVB], psoralen plus ultraviolet A [PUVA], etc.), including indoor tanning; Systemic Chinese herbal medicines or proprietary Chinese medicines; Other systemic medications for the treatment of atopic dermatitis (AD).

3. Receipt of the following topical therapies within 2 weeks prior to baseline:

   Topical corticosteroids (TCS); Topical calcineurin inhibitors (TCI); Topical phosphodiesterase 4 (PDE-4) inhibitors; Topical Chinese herbal preparations or herbal medicated baths; Other topical medications for the treatment of AD.

4. Receipt of allergen-specific immunotherapy within 6 months prior to baseline.

5. Use of strong inhibitors or strong inducers of cytochrome P450 3A (CYP3A) hepatic metabolic enzymes within 2 weeks prior to baseline.

6. Use of long-acting anticoagulants (e.g., warfarin, clopidogrel, etc.) within 4 weeks prior to baseline, or requirement for continuous anticoagulant therapy (excluding aspirin at a dose ≤100 mg per day).

7. Planned administration of live or attenuated live vaccines within 4 weeks prior to baseline; or anticipated need for live or attenuated live vaccines during the study period (including at least 4 weeks after the last dose of investigational product).

8. Participation in any clinical trial involving an investigational product within 4 weeks prior to baseline (or 5 half-lives, whichever is longer), or participation in any clinical trial involving a medical device within 3 months prior to baseline.