If you think smoking marijuana is a hundred percent safer than smoking cigarettes, think again. Scientists from the Dana-Farber Cancer Institute and the Centers for Disease Control and Prevention (CDC) found that people who only smoked marijuana still had several smoke-related toxic chemicals in their system—but at lower levels than those who only or also smoked tobacco. This included three chemicals known to cause liver damage that are also linked to cancer and other health issues. However a fourth chemical that is known to contribute to cardiovascular disease in tobacco smokers was only found in the system’s of those who smoked tobacco. Senior study author Dr. Dana Gabuzda explains, “This increase has renewed concerns about the potential health effects of marijuana smoke, which is known to contain some of the same toxic combustion products found in tobacco smoke.”