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Cocaine use may suppress the immune system

New research funded by the Medical Research Council (MRC) may help to explain why regular cocaine users are far more likely to contract an infectious disease than those with no history of drug addiction.

A study, published this week in the journal Biological Psychiatry, shows that cocaine-dependent men have heightened physical and biological ‘warning’ reactions to visual cues that convey a risk of infection, such as rotten food and dirty toilets.

The research, led by Dr Karen Ersche from the Behavioural and Clinical Neuroscience Institute, University of Cambridge, suggests that these oversensitive bodily reactions may be borne from a history of recurrent infection. Yet, their lack of awareness about their bodies alarm signals could cause cocaine users not to protect themselves adequately, putting themselves even more at risk of contracting an infectious disease.

Infectious diseases are the most common and costly health complications of drug addiction and chronic drug users are at particularly high risk of contracting infections such as HIV, hepatitis B and C, even if they are not injecting drugs. Rates of other infections such as tuberculosis and sexually transmitted diseases are also high amongst people who regularly consume addictive drugs such as cocaine.

Until now it has been widely believed that cocaine users’ high infection rate is due to their tendency to engage in ‘risky behaviours’, such as unprotected sex, or sharing pipes and straws, which exposes them to disease-causing pathogens. It has also been suggested that cocaine itself may interfere with the body’s immune response to infectious agents, like viruses and bacteria, leaving drug users more vulnerable to infection.

The MRC-funded researchers studied 61 men, 31 of whom were cocaine-dependent, and showed them a series of neutral and ‘disgusting’ pictures (examples shown below), which were not related to drug-taking but depicted general scenes involving dirt, decay, wounds and body excrement. They recorded their physical and behavioural response to the pictures by measuring levels of immune activity (cytokines) in their saliva and using a technique similar to a lie detector polygraph to test their unconscious reaction to the pictures. They also asked participants about their personal hygiene habits, for example how often they washed their hands.


The cocaine-addicted group had higher levels of immune chemicals and more pronounced unconscious reactions in response to the disgusting images than the control group. This type of ‘hypersensitivity’ reaction is typical of people who are prone to repeat infections and is due to a type of Pavlovian-like conditioning, where the immune system ‘learns’ to associate unhygienic surroundings with impending illness and, as a result, prepares to fight infection.

Dr Karen Ersche from the University of Cambridge, who led the study, said:

“Our study clearly shows that cocaine users have abnormal responses to situations that might, in the real world, present an infection risk. Although their bodies were highly sensitive to the disgusting pictures, the cocaine users themselves seemed to be unaware of their heightened risk, which may explain why they are not taking special care in protecting themselves and are reluctant to make use of preventative measures on offer for them"

“Our findings bring to light two key points, namely that regular cocaine users need to be made aware of their increased risk for infectious diseases, and researchers need to find out how the immune system in regular cocaine users has changed in order to develop effective treatments to reduce the risk of infections in these people. There may also be wider implications for policies that aim to reduce the harmful consequences of drug use.”


Professor Hugh Perry, Chair of the MRC’s Neurosciences and Mental Health Board, which funded the research, said:

“The MRC is leading a UK-wide strategy for research into addiction and substance misuse, which have a devastating impact on peoples’ lives and society as a whole. By learning more about the consequences of drug use – beyond those we most commonly associate with a life of addiction – we will be able to devise new ways to reduce the harm caused by illicit substances and to help transform lives by breaking the vicious cycle of addiction.”

The researchers are now planning a new study to learn more about the effects of cocaine on the immune system, specifically in the blood, which they didn’t look at in this study. They also aim to explore new avenues of making harm reduction interventions more effective in chronic cocaine users.


Adapted from MRC Press release


Posted on 09/10/2013

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