Patients with substance use and related addictive disorders have higher prevalence of co-morbid mental health disorders compared to general population; and vice versa, the prevalence of substance use disorders is higher among patients with other mental disorders than in general population. Un(der)treated one or both diseases lead to worse treatment outcomes and is associated with several negative physical and psycho-social consequences. However, it is known that some psychoactive substances (eg. stimulants, cannabis) can induce psychiatric side effects such as psychosis, anxiety, mood disturbances and suicidality or worsen the symptoms of previously existed mental disorder. Further, we can monitor the occurrence of new psychoactive substances (NPS) in past few years, so called designer drugs, legal highs, herbal highs, research chemicals,…Beside mimicking the effects of illicit substances and being relatively cheap, they became highly available, mostly through internet smart shops and darknets. There are almost no existing studies about possible short and long term side effects of NPS, but we can find reports of toxicity on physical and mental health – unfortunately, some of them with fatal outcome. The author will present the most frequently used NPS (with focus on synthetic cannabinoides and synthetic cathinones), especially psychiatric side effects, which can be very miscellaneous. A case-report of synthetic cathinone - induced psychosis will be presented to.