Mixing Weed and Tobacco: What Spliffs Do to Your High, Heart and Brain

Mixing weed with tobacco, aka rolling a spliff, can change your high (some people say it hits harder, others say it dulls it), but research links the combo to stronger dependence on both, extra strain on your heart and more lung problems than smoking either one on its own. Cannabis has changed a lot in recent years: in the last decade alone, it's been legalized in several countries and regions, largely thanks to its recognized medical uses. At the same time, more people are consuming it through vaping, edibles or concentrates.

Tobacco and cannabis still have a strange relationship that goes on to this day. So why do so many people consume the two together? Here's what happens when you combine tobacco and weed.

Weed with tobacco: does it change the High?

Plenty of users have reported differences (all of them subjective) between the effects of cannabis on its own and weed mixed with tobacco.

One of the most commonly reported effects of smoking cannabis with tobacco is a more intense head rush, though lots of others say tobacco actually does the opposite and takes the edge off the high.

Another frequently described effect is that it can help "calm" the anxiety cannabis sometimes brings on.

So why does all this happen? The biological mechanisms behind this odd relationship are complex. For starters, they're tied to other processes that we now know are connected, but that were long thought to be independent.

Weed vs. tobacco: the consequences

To understand why people combine the two, several US research centers published the first comprehensive review of the consequences of mixing tobacco and cannabis in 2017. While they concluded that more research is still needed, they did identify several harmful effects:

• Lower perceived risk of using both tobacco and (smoked) cannabis.
• Greater dependence on both substances.
• Stronger subjective effects from cannabis, like its psychoactive or sedating effects.

Other research has found that people who use both cannabis and nicotine are at risk of a decline in normal day-to-day functioning, including worse mental health, lower life satisfaction, more legal problems and less academic success in college.

How tobacco and weed affect your heart

Beyond the many effects this combo can have, one of the areas hit hardest by using cannabis and tobacco together is the cardiovascular system.

That's mainly because nicotine triggers a chain of responses like a racing heart (tachycardia) and higher cardiac output and blood pressure. Cannabis, for its part, alters heart rate too, either speeding it up or, at high doses, slowing it down (bradycardia).

Then there are the effects on blood pressure: it tends to rise when you're sitting or lying down and drop when you stand up. On top of that, cardiac output goes up, exercise tolerance goes down, and health can get worse in people who already have heart or blood vessel conditions.

Cannabis, tobacco and the hippocampus

One recently published study showed that chronic, long-term cannabis use significantly reduced the volume and density of the hippocampus, a brain area linked to memory, inhibition and addiction.

A 2011 study found something similar, but it also found that the effect could depend on several factors, especially the ratio of THC to CBD. Specifically, a higher THC and lower CBD ratio was much more strongly linked to reduced volume in the right hippocampus. The researchers read this as a sign of potential neurotoxic effects from THC and neuroprotective effects from CBD.

More studies on tobacco and weed

Another study found no long-term changes at all, and one study highlighted that genetic differences may change how the hippocampus responds when someone uses cannabis, whether vaped or smoked. In that research, the shrinkage showed up both in cannabis-only users and in people who combined weed and tobacco. It didn't show up in nicotine-only users.

Among people who only used cannabis, a smaller hippocampus was linked to worse memory. Since a healthy, larger hippocampus usually goes hand in hand with better memory in kids, teens and young adults, that's not much of a surprise. In this group, the smaller the hippocampus, the worse the memory.

But the research also turned up something that caught a lot of people off guard: in the cannabis-plus-tobacco group, the opposite happened, and, even more surprisingly, a smaller hippocampus was linked to better memory.

Meanwhile, people who smoked more cigarettes showed a bigger drop in hippocampal volume, yet scored relatively higher on memory tests (though their memory was still generally worse).

The bottom line on tobacco and weed

Despite the mountain of research in recent years, we're still a long way from understanding exactly what goes on in the brain when people take psychoactive substances, alone or together.

And beyond the studies still underway, using tobacco and cannabis together is linked to airway irritation, coughing, more phlegm, bronchospasm, bronchitis, shortness of breath, sore throat, flare-ups of asthma and cystic fibrosis, and the development of chronic bronchitis.

Many researchers have also concluded that smoking tobacco and cannabis together leads to more health problems than smoking tobacco alone. So the tobacco-and-weed combo might not be the best idea: it has real health consequences, both short and long term, possibly even more than when you use them separately.