Introduction. Marijuana use among teenagers is a topic of great concern for parents, educators, and health professionals. As more countries legalize marijuana for recreational and medical use, it is essential to understand the potential long-term effects of its consumption on the mental health of young people. A recent study published in a prestigious scientific journal has found that marijuana use in teenagers doubles the risk of developing serious mental illnesses, such as schizophrenia and major depressive disorder. In this article, we will explore the findings of this study and discuss the implications for public health. # Study methodology. The study in question was conducted by a team of researchers who analyzed data from over 20,000 participants, all of whom were teenagers who had used marijuana at least once in their lifetime. The researchers used a combination of surveys, interviews, and data analysis to assess the risk of developing serious mental illnesses based on marijuana use. The results of the study were clear: teenagers who regularly used marijuana were twice as likely to develop a serious mental illness compared to those who did not use marijuana. # Implications for public health. The findings of this study have significant implications for public health. First, they suggest that marijuana use in teenagers may have long-term consequences for mental health, highlighting the need to educate young people about the risks associated with marijuana use. Second, the results of the study suggest that health professionals should be vigilant for signs of serious mental illnesses in teenagers who use marijuana, in order to provide timely and effective treatment. # Conclusion. In conclusion, the study finds that marijuana use in teenagers doubles the risk of developing serious mental illnesses. These findings have significant implications for public health and highlight the need to educate young people about the risks associated with marijuana use. It is essential that parents, educators, and health professionals work together to prevent marijuana use in teenagers and provide support to those who are already using this substance.