This study is to evaluate the safety, the systemic exposure, and the hypothalamic-pituitary-adrenal (HPA) axis suppression potential for topically applied IDP-118 lotion in pediatric participants with moderate to severe plaque psoriasis.

Inclusion Criteria:

• Is 4 to 16 years 11 months of age at time of informed consent/assent obtained.
• Verbal and written informed consent/assent obtained from the participant and/or parent or legal guardian.
• Has a clinical diagnosis of psoriasis at Screening and Baseline with an Investigator's Global Assessment (IGA) score of 3 or 4. The face, scalp, axillae, and intertriginous areas are to be excluded in this assessment, if psoriasis is present.
• Has an area of plaque psoriasis appropriate for topical treatment that involves a BSA of at least 10% at Screening and Baseline. The face, scalp, axillae, and intertriginous areas are to be excluded in this calculation.
• Is willing and able to avoid prolonged exposure of the treatment area to ultraviolet radiation (natural and artificial) for the duration of the study.
• Is in good general adrenal health, as determined by a 30-minute postcosyntropin stimulation serum cortisol level that is >18 μg/dL at the Screening visit.
• Females of childbearing potential and females who are pre-menses (9 years and older) must be willing to practice effective contraception for the duration of the study.

Exclusion Criteria:

• Has a history of adrenal disease.
• Presents with any concurrent skin condition that could interfere with the evaluation of the treatment areas, as determined by the Investigator.
• Is pregnant, nursing an infant, or planning a pregnancy during the study period.
• Has received treatment with any investigational drug or device within 60 days or 5 drug half-lives (whichever is longer) prior to baseline or is concurrently participating in another clinical study with an investigational drug or device.
• Received treatment with a topical antipsoriatic drug product other than corticosteroids within 14 days prior to the Baseline visit and/or treatment containing corticosteroids within 28 days prior to the screening HPA axis stimulation test.
• Has a history of hypersensitivity or allergic reaction to any of the study drug constituents.
• Is considered by the Investigator, for any other reason, to be an unsuitable candidate for the study.