Study is First to Show Cocaine Compromises Immune Response and May Increase Risk of Infection

March 05, 2003

Public Affairs

Belmont, MA - Cocaine users tend to be susceptible to infections, including HIV. However, now researchers at McLean Hospital have shown that cocaine reduces the response of an essential immune system messenger compound, thus altering the body's defenses against disease.

Reporting in the March issue of the Journal of Clinical Endocrinology and Metabolism (abstract), Principal Investigator John Halpern, MD, of McLean Hospital's Alcohol and Drug Abuse Research Center says the results are clear: "If you use cocaine even once, while you're using it, your body is not going to fight off an infection the way it is designed to."

The study tracked the response to the immune system compound called Interleukin-6 (IL-6) as well as several hormones. IL-6 belongs to a group of immune system regulators called cytokines. They have been described as the "hormones of the immune system." They are released in response to stress on the body, damage to the body or infectious agents. In particular, Interleukin-6 is involved in many initial immune reactions, such as antibody production, differentiation of B cells and activation of T-cells. The data shows that within four hours after cocaine injection, the drug dramatically reduced the response of IL-6 compared to those injected with saline placebo.

Researchers exposed subjects to a foreign object in the form of an intravenous catheter (IV) placed in one arm to measure the response of IL-6. All IVs cause an inflammatory immune response and generally must be relocated every few days; therefore, IL-6 levels are expected to rise at the IV site. Following cocaine injection in the opposite arm, blood samples were taken at the IV site from 16 healthy women and 14 healthy men between ages 21 and 35 with a history of cocaine use. For IL-6 measurements, in the men, samples were obtained at baseline and five-time intervals, with the last four hours after the cocaine infusion; in the women, samples were obtained at baseline and at four hours after the infusion only.

In the men, IL-6 was 68 percent lower after cocaine than after placebo; in women the IL-6 response was 66 percent lower following cocaine compared to placebo. Researchers believe that cocaine blunts IL-6 release via stimulation of the hypothalamic-pituitary-adrenal (HPA) axis, the areas responsible for hormone production and immune system response and regulation.

Halpern believes these results could explain why so many cocaine users get sick.

"It's not just that the needles are dirty or that many users also engage in risky sexual behavior, it may be the cocaine itself is priming the tissue not to respond adequately. What's scary is that the drug makes it more likely that an infection will take hold, even something like HIV."

Researchers hoped to find a difference in response between men and women and within two different phases of the menstrual cycle in women. However for IL-6, and other hormones, these differences were not apparent and may have been due to small sample size.

Researchers acknowledge the study's limitations and where further study may reveal new information. Suggestions include using natural antigens or viruses rather than a venous catheter to assess IL-6 response; administering the drug intra-nasally to compare immune response to the results seen in this study; and measuring the response of other immune system cytokines.

Still researchers believe the findings should send a message to even casual users. "This is another example of how cocaine can silently and immediately do harm," says Halpern.

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