Smoking cannabis with tobacco increases risk of dependence

Research, published this week in Frontiers in Psychiatry, finds that individuals who smoke cannabis with tobacco have less motivation to quit than those who smoke it without tobacco.

[Youth smoking cannabis]
Smoking cannabis with tobacco might have different implications from smoking them independently.

Cannabis and tobacco are among the most popular drugs on earth.

Tobacco is use by an estimated 1 billion people (around 22.6 percent of all adults) and cannabis by 147 million.

Tobacco’s negative health consequences are well known and include cardiovascular disease and cancer.

The long-term health implications of cannabis abuse are less well-documented but are thought to include effects on cognitive performance, psychological dependence, and some cancers.

Using both drugs is common, and many use both compounds in unison – for instance, in joints. This might be to save money by mixing in relatively cheaper tobacco, or because adding tobacco to cannabis can increase the efficiency of cannabis inhalation.

Because of this mixing, separating out the causes and effects of each drug can be challenging. This relationship is clinically important; studies have found that individuals who use cannabis with tobacco have an increased chance of developing negative cannabis-related outcomes, even when results are adjusted for those that use cannabis and tobacco independently.

Studying cannabis and tobacco use

For the first time, researchers from the Clinical Psychopharmacology Unit of University College London, United Kingdom, set out to pick this interaction apart.

The research was a concerted effort between a number of institutions, including University College London, King’s College London, the South London and the Maudsley National Health Service (NHS) Trust, and the University of Queensland in Australia.

Questionnaire data from 33,687 cannabis users was taken from the 2014 Global Drug Survey, an anonymous online survey that asked questions about drug use. Participants came from 18 countries across the Americas, Australasia, and Europe. The average age was 27.9 and females accounted for 25.9 percent of participants.

The study produced a wealth of detail; one of the most pertinent findings was in regards to addiction:

“Cannabis is less addictive than tobacco, but we show here that mixing tobacco with cannabis lowers the motivation to quit using these drugs.”

Chandni Hindocha, lead author, University College London

Regional variation in cannabis smoking methods

The team found that the method by which individuals used cannabis differed widely between countries. For instance, tobacco routes for cannabis, including blunts and joints, were much more popular in Europe than elsewhere.

Around 77.2-90.9 percent of European cannabis smokers chose tobacco routes, the researchers report, depending on the country. Only slightly more than half of Australians (51.6 percent) used tobacco routes, compared with just 20.7 percent in New Zealand.

Tobacco routes were least popular in the Americas: Canada, 16 percent; United States, 4.4 percent; Mexico, 6.9 percent; and Brazil, 7.4 percent.

Conversely, vaporizers – a non-tobacco route – were quite common in Canada (13.2 percent of users) and the U.S. (11.2 percent), but infrequent elsewhere – 0.2-5.8 percent.

Cannabis route and addiction

Importantly, the researchers found that the route by which cannabis was taken influenced users’ motivation to quit, and the likelihood that they would search for help in quitting.

Individuals who used non-tobacco routes more regularly were 61.5 percent more likely to want professional help to use less cannabis. They also had an 80.6 percent higher chance of wanting help to use less tobacco when compared with individuals who favored tobacco routes.

In a similar vein, those using non-tobacco routes more frequently had a 10.7 percent higher chance of wanting to use less tobacco and a 103.9 percent higher chance of actively seeking help to reduce tobacco intake.

“Our results highlight the importance of routes of administration when considering the health effects of cannabis and show that the co-administration of tobacco and cannabis is associated with decreased motivation to cease tobacco use, and to seek help for ceasing the use of tobacco and cannabis.”

Michael T. Lynskey, professor of addictions, King’s College London

Other tobacco and cannabis-related findings

The study generated a wealth of interesting results, including the following:

  • Joints are smoked by 93.4 percent of cannabis users who prefer tobacco routes
  • The pipe is the most popular non-tobacco cannabis route, used by 11.7 percent of those who prefer the non-tobacco route
  • Only 2.4 percent of cannabis users worldwide chose non-inhaled routes, such as bucket bongs, hot knives, or in food and drink
  • Men are more likely to use tobacco routes than women (68.2 percent, compared with 63.8 percent)
  • On average, users of the tobacco route are younger than those using non-tobacco routes – 26.2 years, compared with 30.8 years
  • More than 16 percent of respondents had never smoked tobacco without cannabis.

The findings come at a pivotal time in the political cycle of cannabis and tobacco usage.

“Given a changing legislative environment surrounding access to cannabis in many jurisdictions, increased research focus should be given to reducing the use of routes of administration that involve the co-administration of tobacco.”

Michael T. Lynskey

The current findings support previous studies that suggest tobacco increases the overall dependence on cannabis. Further research along similar lines will help shape recommendations and design more effective quitting programs for both drugs.

Learn about cannabis and its relationship with another popular drug – alcohol.