Background: Despite solutions presented by the European Union and national regulations introduced by many countries, the problem of
mephedrone (4-MMC) is growing. Objectives: The aim of this study was to investigate the effect of regular
mephedrone intake with other psychoactive substances on the clinical picture of patients, including self-harms and suicide attempts. Methods: The study involved a group of 601 patients addicted to
mephedrone who were admitted to a psychiatric hospital between 2010 and 2018 due to regular
mephedrone intake. Results: There was a statistically significant relationship between
sleep disorders and
mephedrone combined with alcohol (p < .05) or cannabinols (p < .05). However, the highest number of statistically significant correlations was reported when
mephedrone was combined with
opioids. There was a growing year-on-year percentage of people who attempted suicide because of regular
mephedrone intake (p < .001). The more psychoactive substances were combined with
mephedrone, the greater the risk of attempted suicide (p < .01). 20% of the examined group were hospitalized several times. Among those hospitalized several times, significantly more people took more than one additional psychoactive substance (p < .01). Conclusions: The more psychoactive substances combined with
mephedrone, the more clinical symptoms are associated with it.