Stress is a risk factor in the development of addiction. The ‘self-medication’ model proposed by Gelkopf et al. (2002) suggests that some people deliberately deal with everyday stressors by using different types of pathological behaviour (alcohol, drugs and/or gambling) in order to make themselves feel better. Research by Dawes et al. (2000) has shown that stress is one of the strongest predictors of relapse in drug users. Research has also showed that severe stress can make people more vulnerable to developing an addiction. For example, Kessler et al. (1995) found that 34% men and 27% of women with a history of post-traumatic stress disorder (PTSD) reported drug abuse or dependence at some point in their lives (compared with 15% of men and 8% of women who did not have PTSD).