The antidepressant Celexa (citalopram) increases the activity of natural killer (NK) cells—a critical line of defense against cancer and infectious diseases like HIV—say the authors of a new study published in the May 1 issue of Biological Psychiatry and reported by ScienceDaily.

NK cells are able to recognize and destroy immune cells that are infected with HIV or that have begun to grow abnormally, as is the case with cancer. It has been shown that the level and activity of NK cells are often lower in both people with HIV and people who are depressed.

Dwight Evans, MD, from the Joseph J. Stokes Research Institute of the Children’s Hospital of Philadelphia, and his colleagues enrolled 51 HIV-positive patients into a study to determine the effect of different drugs on NK cell activity. Evans’s team found that Celexa and a second drug called CP 96,345 enhanced the activity of NK cells.

Further studies will likely be necessary to determine whether the enhanced NK activity induced by Celexa and CP 96,345 has a clinically meaningful effect on HIV, says Evans, who concludes that such drugs may “possibly [delay] HIV disease progression and [extend] survival with HIV infection.”