Cannabis does not become any more rewarding when combined with tobacco, according to new research published in the journal Psychopharmacology.

“Cannabis and tobacco are two of the world’s most commonly used drugs, and around the world they are also used together in the same product (“joint”, “spliff”) but when we consider the use of cannabis, we tend to forget that it’s often mixed with tobacco (77.2% of cannabis users in the last year, in the UK, used tobacco in their joints),” the study’s lead author, Chandni Hindocha of University College London, told PsyPost.

“Given that both drugs have reinforcing effects, we wanted to know if cannabis and tobacco, individually and combined, affected your ‘wanting’ and ‘liking’ of both drug and non-drug reward types – in particular, food, given that cannabis has a classical symptom – the munchies. It’s an important topic as we often consider the importance of the rewarding effects of cannabis but do not consider that most smoke it with tobacco.”

The double-blind placebo-controlled study of 24 smokers found no evidence that tobacco influenced the rewarding effects of cannabis.

“Participants came in the lab four times and each time they smoked a different combination of cannabis and tobacco together in a joint (active cannabis + active tobacco, active cannabis + placebo tobacco, placebo cannabis + active tobacco, and placebo cannabis + placebo tobacco),” Hindocha said.

“They completed tasks asking them how much cannabis and tobacco they wanted to smoke, how much they liked cannabis/tobacco drug-related images, and measures of craving.”

The researchers found that people under the influence of cannabis viewed cannabis-related imagery as less pleasant but viewed food-related imagery as more pleasant, compared to placebo.

The participants were also asked how many cigarette or cannabis puffs they would be hypothetically willing to buy in the next 3 hours, at increasing prices. But people under the influence of cannabis became significantly less likely to buy cigarettes or cannabis at higher prices.

“Forty-one percent of the data regarding demand for cannabis was missing because once a participant had smoked the active cannabis in the study they no longer wanted any more cannabis,” Hindocha explained.

“Another way to do this study is a to do a self-administration study of individual and combined cannabis and tobacco in humans, which would have provided a direct demonstration of the abuse potential of the drugs combined relative to their components.”

A second study published in Psychological Medicine, which used data from the same experiment, reported that combining tobacco and cannabis did not improve the experience of being stoned.

Hindocha said the findings had a clear take away message: “there’s no point adding tobacco to cannabis.”

The study, “Individual and combined effects of cannabis and tobacco on drug reward processing in non-dependent users“, was co-authored by Will Lawn, Tom P. Freeman, and H. Valerie Curran.