Experts say oxytocin, a key hormone made naturally by the brain, could hold the key to treating drug addicts and help them avoid relapse.

Oxytocin is most usually associated with childbirth and breast feeding, but has multiple psychological effects, influencing social behaviour and emotion.

Sometimes called the 'love hormone', it has an anti-anxiety effect, and many studies have examined the role of oxytocin in addiction.

Researchers at St George's, University of London, after reviewing all the published evidence on oxytocin, have now found that the oxytocin system is profoundly affected by opioid use and abstinence.

The review, which includes seminal studies conducted by Dr. Alexis Bailey's group, suggests the oxytocin system can be an important target for developing new medicines for the treatment of opioid addiction and prevention of relapse among addicts.

Taking drugs activates pathways in the brain that induce pleasurable effects, which make the user want to repeat the experience, but as drug use continues, brain tolerance to the effects of the drug increases and a greater dose is needed to achieve the same effects.

Dr Alexis Bailey, senior author of the review, said: "Given the benefits that social support programmes like Alcoholics Anonymous and Narcotics Anonymous have in keeping addicts abstinent, our findings in the review suggest the use of oxytocin, the pro-social hormone, could be an effective therapy for the prevention of relapse to drug use in drug-dependent individuals.

"Since the evidence is so clear, the need for clinical studies looking into this is obvious."

The study "Oxytocin and opioid addiction revisited: Old drug, new applications" was published in British Journal of Pharmacology.