Adrenal suppression effects of corticosteroids are among the most important safety concerns for this group of products. This study is to determine and compare the adrenal suppression potential and the pharmacokinetic (PK) properties of 188-0551 Spray versus an FDA-approved drug (also known as a "Reference Listed Drug" [RLD]) under maximal use conditions when applied twice daily (approximately every 12 hours) in adult subjects with stable, moderate to severe, plaque psoriasis.

Inclusion Criteria:

• Subject is a male or non-pregnant female and is at least 18 years of age at the time of informed consent.
• Subject has provided written informed consent.
• Subject has moderate or severe psoriasis involving a minimum of 20% Body Surface Area (BSA).
• Subject has an Investigator's Global Assessment (IGA) score of at least three (3 = moderate) at the Baseline Visit.

Exclusion Criteria:

• Subject is pregnant, lactating, or is planning to become pregnant during the study.
• Subject has spontaneously improving or rapidly deteriorating plaque psoriasis.
• Subject has a physical condition which, in the investigator's opinion, might impair evaluation of plaque psoriasis, adrenal axis function or which exposes the subject to an unacceptable risk by study participation.
• Subject has had prolonged exposure to natural or artificial sources of ultraviolet radiation.
• Subject is currently enrolled in an investigational drug or device study.
• Subject has clinically significant abnormal labs at Visit 1/Screening that precludes topical steroid use, in the opinion of the investigator.