Tobacco and cannabis have a strange relationship, one that has lasted for centuries but has been continually turbulent. Why do so many people use the two together? As usual with cannabinoid science, the truth is stranger than anything that could be dreamed up.
Tobacco and cannabis are very often consumed together
Tobacco has been mixed with cannabis for centuries, throughout the world (© Wikimedia Commons)
Tobacco has been mixed with cannabis for centuries, throughout the world (© Wikimedia Commons)
The two substances have been consumed together for centuries by people throughout the world, in Europe, Africa and Asia. In fact, it is thought that up to 70% of people that use cannabis also use tobacco. Even in North America, where cannabis is traditionally smoked pure, many users also use tobacco.
Furthermore, there are many users in North America who smoke cigarettes immediately after smoking cannabis, who are likely to experience similar synergistic effects to those that actually mix the two together (indeed, many do so for the perceived experience of getting “more high” as a result).
Differences in effect are widely reported
Many users report subjective differences between the effects of cannabis alone and cannabis when mixed with tobacco.
The most common reported effect of smoking tobacco alongside tobacco is an intensification of the “high”, although some report that tobacco use actually has the opposite effect and reduces the high. Another commonly reported effect is to “calm” the user down from the sometimes anxiety-inducing effects of cannabis.
The biological mechanisms underlying this strange relationship are wildly complex, and are linked to various other processes now known to be related but long believed to be essentially separate. Indeed, the more we learn about these interlinked systems of reward, craving, addiction, and satiety, the more we begin to understand that every aspect of our brains and bodies is inseparably intertwined.
Cannabis, tobacco and the hippocampus
The hippocampus is an area of the brain that somewhat resembles a seahorse, and is the HQ of the interlinked processes of stimulus, reward and addiction (© Wikimedia Commons)
The hippocampus is an area of the brain that somewhat resembles a seahorse, and is the HQ of the interlinked processes of stimulus, reward and addiction (© Wikimedia Commons)
A widely-reported recent study correlated cannabis use with reduced volume and density of the hippocampus, an area of the brain that is associated with memory, inhibition and addiction. This was also demonstrated in this study from 2011, although the effect here was found to depend on various factors including ratio of THC to CBD. At least one other study has found no long-term change, and one study highlighted the possibility that genetic differences may alter the hippocampal response to cannabis use.
This reduction in size was found both in cannabis-only users and in cannabis/tobacco users, and was not found in nicotine-only users. In cannabis-only users, the small hippocampus was found to correlate with poor memory (this is unsurprising, as good hippocampal health and size usually correlates positively with good memory). So, within the group, the smaller the hippocampus, the poorer the memory.
However, the researchers also found something very surprising indeed: in the cannabis/tobacco-using group the reverse was true, and smaller hippocampal volume correlated with improved memory! Subjects that smoked higher numbers of cigarettes exhibited greater decreases in hippocampal volume, and relatively higher memory scores (although memory was still generally poorer than in all other groups).
While this study was limited in scope and design, and establishes correlation but not causation (as a cross-sectional study looking at a brief window of time, it is inferior to a longitudinal study, for instance, which would follow subjects for extended time periods to better track changes and establish causation), it still demonstrates an unusual effect, and one that has yet not been fully explained.
How all the main regulatory and signalling systems are linked
It now appears that tobacco, cannabis, and other psychoactive substances such as opioids are all linked together in a complex network of stimulus and reward, with the hippocampus essentially functioning as the HQ for operations.
Throughout the body, and particularly in the brain, we have cannabinoid receptors (as our readers will no doubt be aware!), as well as opioid and nicotinic receptors. Within the brain, densities of these receptors are extremely high in the hippocampus, and are also very high in the amygdala (both areas are heavily associated with stimulus, reward, addiction and so on).
The agonists (activators) of these three types of receptors (of which the best known are THC for the cannabinoid receptors, nicotine for the nicotinic receptors, and morphine for the opioid receptors) are hugely important in terms of the psychoactive and ph