A Proof of Concept Study Comparing Three Doses of an Oral Solution of LEO 22811 With a Placebo Oral Solution for the Treatment of Psoriasis Vulgaris

Inclusion Criteria: * Following verbal and written information about the trial the subject must provide signed and dated informed consent before any study related activity is carried out, including activities relating to the washout period. * Clinical diagnosis of psoriasis vulgaris, for at least 6 months prior to randomisation, and currently covering at least 10% of the body surface area (BSA) * Candidates for systemic anti-psoriatic treatment * Psoriasis Area and Severity Index (PASI) ≥10 * Disease severity of moderate, severe or very severe according to the Investigators' Global Assessment of disease severity (IGA) * Aged 18 years or above * Any race or ethnicity * Males, surgically sterile females (bilateral tubal ligation, bilateral oophorectomy or hysterectomy) or post menopausal females (at least 1 year since last menses) * Attending hospital outpatient clinic or the private practice of a dermatologist Exclusion Criteria: * Systemic treatment with biological therapies whether marketed or not with a possible effect on psoriasis vulgaris within the following time periods prior to randomisation: * Etanercept - 4 weeks * Adalimumab, alefacept, infliximab - 2 months * Ustekinumab - 4 months * Systemic treatment with all other therapies (other than biologics) with a possible effect on psoriasis vulgaris (e.g.corticosteroids, retinoids, immunosuppressants, methotrexate, cyclosporin or fumaric acid) within 4 weeks prior to randomisation * PUVA therapy within 4 weeks prior to randomisation * UVB therapy within 2 weeks prior to randomisation * Any topical treatment (except for emollients/ medicated shampoo) within 2 weeks prior to randomisation * Initiation of, or changes to concomitant medication that could affect psoriasis vulgaris (e.g. beta-blockers, anti-malaria drugs, lithium) 2 weeks prior to randomisation and during the study * Current diagnosis with erythrodermic, exfoliative or pustular psoriasis * Other current skin conditions that may confound the evaluation of psoriasis vulgaris as judged by the Investigator * Generally in good health and does not have any clinically significant cardiac, endocrinologic, pulmonary, neurologic, psychiatric, hepatic, renal, haematologic, or gastrointestinal disease, immunologic insufficiency, or other major diseases or current condition which, in the opinion of the Investigator, would put the subject at risk by participating in the study * Current active tuberculosis or latent tuberculosis * Planned exposure to the sun during the study that may affect psoriasis vulgaris * Known malignancy or history of malignancy (other than cervical carcinoma in situ, basal cell or squamous cell carcinoma) within the 5 year period prior to randomisation * Live vaccination within the 4 weeks prior to randomisation * Males who do not agree to use adequate contraception during the study (including follow-up) to ensure their partner does not become pregnant * Known or suspected hypersensitivity to component(s) of the investigational product * Current participation in any other interventional trial * Treatment with any non-marketed drug substance (i.e. an agent which has not yet been made available for clinical use following registration) within 4 weeks or 5 half-lives (whichever is longer) prior to randomisation * Previously randomised in this study * Known or, in the opinion of the Investigator, is unlikely to comply with the Clinical Study Protocol (e.g., alcohol abuse, drug dependency or psychotic state).