The purpose of this study was to evaluate the safety and effectiveness of an investigational drug called doxercalciferol in participants with moderate to severe chronic plaque psoriasis, in comparison with a placebo ("sugar pill"). All study related care was provided including doctor visits, physical exams, laboratory tests and study medication. Total length of participation was 28 weeks.

This was a multicenter, randomized, double-blind, placebo-controlled, dose-ranging, parallel group study to evaluate the efficacy and safety of doxercalciferol given orally, once daily for 24 weeks to participants with moderate to severe chronic plaque psoriasis. Participants were randomized and stratified by site and Psoriasis Area Severity Index (PASI) score to one of three active treatment groups or to the placebo group.

Inclusion Criteria:

• Participant had moderate to severe chronic plaque psoriasis defined by a body surface area (BSA) involvement greater than or equal to (>=) 10 percent (%) and plaques with at least a slight elevation above the surrounding normal skin at the Day 1 visit
• Participant had a static Physician's Global Assessment (PGA) of moderate or severe at the Day 1 visit
• Participant had a minimum PASI score of 10 at the Day 1 visit
• Participant was a candidate to receive systemic psoriasis therapy in the opinion of the Investigator
• Participant of childbearing potential, was willing to use an effective contraceptive method throughout the study, which included barrier methods, hormones, or intrauterine devices

Exclusion Criteria:

• Used vitamin D analogues, multivitamin supplements containing greater than (>) 400 international unit (IU) vitamin D, topical retinoids, topical pimecrolimus, and topical tacrolimus within 14 days prior to the Day 1 visit
• Used drugs known to influence serum calcium (such as lithium, digoxin, thiazide diuretics, teriparatide, bisphosphonates, and calcitonin) and multivitamin supplements containing calcium and/or calcium-containing antacids exceeding a total of 1 gram/day within 14 days prior to the Day 1 visit
• Used keratolytics or coal tar (except shampoo containing coal tar or salicylic acid) within 14 days prior to the Day 1 visit
• Used low potency topical corticosteroids (Classes VI and VII), except on the groin, scalp, palms, soles and face, within 14 days prior to the Day 1 visit
• Used medium potency topical corticosteroids (Classes III - V) or high potency topical corticosteroids (Classes I and II) within 14 days prior to the Day 1 visit
• Used systemic retinoids, systemic corticosteroids, methotrexate, cyclosporine, azathioprine, thioguanine or other systemic immunosuppressant agents within 28 days prior to the Day 1 visit
• Used phototherapy, including Ultraviolet B within 14 days or Psoralen plus Ultraviolet A within 28 days prior to the Day 1 visit
• Used a biological agent (including, but not limited to, etanercept, adalimumab, efalizumab, infliximab, or alefacept) within 5 half-lives of the drug prior to the Day 1 visit
• Used systemic antibiotics within 14 days prior to the Day 1 visit. Antibiotic treatment of infections during the Treatment Period was not excluded
• Used investigational drugs within 28 days prior to the Day 1 visit
• Current erythrodermic, guttate, generalized pustular, unstable psoriasis or other chronic active skin conditions that may interfere with the study
• Screening visit laboratory result exceeded the following limits: alanine transaminase (ALT) or aspartate transaminase (AST) >1.5 times the upper limit of normal (ULN); bilirubin >ULN; serum creatinine, calcium, or phosphorus >ULN; spot urine calcium/creatinine ratio >0.4
• History of nephrolithiasis
• Chronic kidney disease as evidenced by a calculated glomerular filtration rate (GFR) less than (<) 60 milliliter/minute/1.73 square meter (mL/min/1.73 m^2) at the screening visit
• Symptomatic coronary or cerebral vascular disease, human immunodeficiency virus, active viral hepatitis, or any other clinically significant, unstable medical condition that would interfere with the completion of the study
• Clinically significant electrocardiogram (EKG) abnormality at screening
• Any evidence of active malignancy except for basal cell carcinoma of the skin. A history of malignancy was not an exclusion
• Active ethanol or drug abuse, excluding tobacco use
• Active severe psychiatric illness that could interfere with the conduct of the study
• Pregnant or breast-feeding women
• Known allergy or hypersensitivity to vitamin D or other ingredients in the study drug formulation