Rationale:  Ample evidence supports the contention that alcohol and tobacco act as “gateways” to cannabis use. This study evaluated the bidirectional gateway effects of these substances to ask whether or not cannabis can act as a gateway to other drugs. 

Method: Survey data from 4,031 young adults in the United States was used to establish the sequence of use for cigarettes, e-cigarettes, cigars, alcohol, and cannabis by comparing age of first use. Hazard Ratios (HRs), predicted increased risk of initiating use of a substance based on initiation of other substance use.

Results: Researchers found strong bidirectional gateway effects, with significant increased hazards in both directions. Replicating previous research, using cigarettes, e-cigarettes or alcohol increased the likelihood of initiative cannabis use 3.78, 2.17 and 3.41 times, respectively.

However, cannabis initiation also significantly increased the risk of initiating other substances: cigarettes: 3.51 times e-cigarettes: 3.73 times, and alcohol: 3.07 times. Gateway effects were stronger when the use began at younger ages (15–18 years) compared to after age 18.

Meaning: This study confirms and extends gateway effects of addictive drugs. Cannabis use strongly predicted the subsequent initiation of nicotine products and alcohol, especially for those under 18. Because early use of addictive drugs also predicts disordered use, it’s important to be aware of long-term risks before starting.