The finding, published in The Lancet, comes from a study of 618 people with moderate to severe psoriasis.
The researchers included Stephen Tyring, MD, of the dermatology department at the University of Texas Health Science Center, and Ranga Krishnan, MD, a professor of psychiatry and behavioral sciences at Duke University Medical Center.
"At this point, no one should run to their doctor and ask for this drug for depression," Krishnan continues. "However, the science is very exciting to us."
Enbrel blocks an inflammatory chemical called tumor necrosis factor alpha (TNF-alpha). TNF-alpha has been linked to fatigue and sleepiness, and it may also be connected to depression, according to background information in the study.
Psoriasis and Depression
Psoriasis is a common, chronic condition marked by patches of itchy, scaly, and sometimes inflamed skin, often on the elbows, hands, feet, scalp, or back.
Some psoriasis cases are mild. Others are severe, leaving patients feeling self-conscious, isolated, and depressed.
"Depression, substance abuse, and suicidality are common and problematic in patients with psoriasis," write Tyring and colleagues.
The Enbrel study lasted three months. During that time, all patients got two weekly injections.
Half of the patients got shots of Enbrel. The others got shots containing no medicine (placebo). No one knew which patients received Enbrel.
Patients rated their depression and fatigue at the study's start and during the fourth, eighth, and 12th weeks. They were also screened by a researcher for depression.
Depression, Fatigue Before Treatment
At the study's start, about a third of participants in both groups appeared to be mildly to severely depressed.
The patients also reported more fatigue than the general public, the researchers note.
Depression, Fatigue After Treatment
Depression and fatigue eased for both treatment groups, with bigger gains reported for patients taking Enbrel.
By the study's end, depressed patients had significant improvements in areas including sexual symptoms, interest, appearance, and work or other activities.
More patients taking Enbrel also reached the study's goal for improvement in joint and skin problems caused by psoriasis. That goal was reached by 47% of the Enbrel group, compared with 5% of the placebo group.
The most common side effects were reactions at the injection sites. Infections were more common in the Enbrel group but not by much, the researchers note.
"Surprisingly, the majority of patients in this study did not have significant depression at baseline, by contrast with what is known about the general psoriasis population," write Tyring and colleagues.
They suggest that the study's design might partly explain that. Patients were excluded if they had a history of psychiatric disorders that might interfere with study participation.
The study was partly designed by Immunex, which invented Enbrel. Immunex and Wyeth Research funded the study. Amgen, which now owns Immunex, provided "editorial assistance" in writing the paper, the researchers write.