Marijuana use is associated with an increased risk of physical violence in relationships among young people, according to study recently published in Drug and Alcohol Dependence.

In the USA the law regarding marijuana is changing. Over 20 states have decriminalized the use of marijuana and 35 states have made it legal for medical use. Young adults are thought to be most affected by these policy changes because they face an important stage in their development into adulthood but also have the highest reported rates of marijuana use.

According to the Substance Abuse and Mental Health Services Administration as many as 20% of 18-25 year olds report using marijuana in the past 30 days. The general concern is that as the law regarding marijuana relaxes there will be an increase in associated behavioural problems.

Physical dating violence (PDV) is a behavioural problem that is thought to be influenced by marijuana use. To date there is little evidence for this claim. However, there is a well established link between alcohol consumption and PDV among young people. This evidence displays how important it is to investigate the potential association between using mind-altering substances and the risk of physical violence in relationships.

Renee Johnson (John Hopkins Bloomberg School of Public Health) and team, investigated the current understanding of the link between marijuana use and both PDV victimization and perpetration by combining data from several studies in a meta-analysis.

The results showed that there is an association between marijuana use and PDV victimization among adolescents. The association was strongest in females. The results also revealed an association between marijuana use and PDV perpetration. Again, this association was particularly observed in adolescent females.

Overall the study brought together a large amount of existing data to determine the link between marijuana and PDV, providing a solid basis for further research to be carried out. The link between marijuana use and PDV is strongest amongst adolescent girls. However, several studies that were included in the meta-analysis did not provide support for an association between marijuana use and PDV. These studies had an older participant age range for example 18-27. Which suggests that the behavioural effects of marijuana have a greater impact on teenagers rather than young adults.

As the laws about marijuana use change it is important to develop our understanding of the associations between marijuana use and specific public health problems. Particularly in adolescents due to their sensitive developmental stage and high level of marijuana use.