While the United States marks a historic fall in cigarette smoking, public health researchers are warning that a quieter and more complex health risk is growing alongside it. New evidence suggests that cannabis legalisation has not simply replaced tobacco use, but has increased the number of people using both cannabis and tobacco together, creating what experts describe as a “double dependency”.

The findings come from an analysis of health behaviour data published in the peer-reviewed journal Tobacco Control. The study draws on the US Behavioral Risk Factor Surveillance System, an annual survey run by the Centers for Disease Control and Prevention (CDC) and state health departments. Researchers analysed responses from 854,878 adults aged 18 and above, collected between 2016 and 2023 across 38 states.

Their conclusion challenges a popular assumption. While sole tobacco use fell by 13% after cannabis legalisation, the likelihood of concurrent use of both tobacco and cannabis rose by 44%. In simple terms, fewer people are only smoking cigarettes, but many more are now using cigarettes or vapes alongside cannabis.

“Concurrent use means consuming both substances within the same period, not necessarily at the same time,” the researchers explained. “This pattern is important because emerging evidence suggests that using both together increases the risk of dependence and may worsen health outcomes compared to using either alone.”

US states have been legalising cannabis for recreational use since 2012, and by July 2025, 24 states and Washington DC had allowed adult use for those aged 21 and above. Legalisation coincided with a general fall in tobacco use, long driven by strict regulations and public awareness campaigns. However, cannabis use rose across almost all age groups, including a notable increase among older adults aged 65 and above.

From 2016 to 2023, sole tobacco use remained broadly stable at around 14%, while sole cannabis use hovered near 7%. Concurrent use, however, increased from just over 4% to nearly 5.5%. Rates varied widely between states, ranging from 3% in Utah to 9.5% in Alaska.

The rise was particularly marked among higher-risk groups. Younger adults, men, single individuals, those without health insurance, and people reporting poor mental health or heavy alcohol use were more likely to use both substances. Interestingly, cannabis use also increased among groups that traditionally reported lower use, such as older adults and people with higher education levels.

Public health experts say this trend matters because dependence works differently when substances are combined. “Nicotine and cannabis can reinforce each other’s addictive effects,” one public health specialist noted. “This makes quitting harder and may increase long-term harm to the lungs, heart, and mental health.”

The researchers were careful to stress that the study is observational, meaning it cannot prove cause and effect. The data relies on self-reported behaviour and does not capture how often or in what way tobacco and cannabis are used together. Only 38 states were included, so results may not reflect the entire country.

Even so, the warning is clear. “Our findings add to growing evidence that adults are shifting product use in response to cannabis legalisation,” the authors wrote. They cautioned that greater access through retail stores and rising perceptions that cannabis is “safe” may unintentionally encourage co-use, even as tobacco control policies continue to work.

For countries like India, which already carry one of the world’s highest tobacco burdens, the message is relevant. As debates around vaping, harm reduction, and cannabis policy evolve globally, experts say the US experience shows that reducing one addiction does not automatically reduce overall harm.

As cigarette smoking declines, many are asking whether cannabis is a safer alternative. Evidence suggests it is not—especially when cannabis is used alongside tobacco. Researchers warn that combining the two increases the risk of dependence and may worsen damage to the lungs, heart and mental health. While cannabis legalisation has helped reduce sole cigarette use, it has also been linked to a rise in people using both substances together. Younger adults and those facing mental health challenges appear most vulnerable to this dual dependence, raising a broader policy concern: when access to addictive products expands faster than public understanding of their risks, well-intended reforms can unintentionally fuel new patterns of addiction.