Reefer research: cannabis 'munchies' explained by new study
Besides making a bongo drum sound
inexplicably magical and enhancing a
person’s ability to talk nonsense for
extended periods of time, generations of
cannabis smokers will recognise the
“munchies” as one of the drug’s most
reliable side-effects.
Now scientists have shown that the
insatiable urge to eat after smoking is
caused by cannabinoids hijacking brain
cells that normally suppress appetite. The
study suggests that cannabis causes the
brain to produce a different set of
chemicals that transform the feeling of
fullness into a hunger that is never quite
satisfied.
Scientists believe the findings, which
illuminate a previously unknown aspect of
the brain’s feeding circuitry, could help
design new drugs that would boost or
suppress appetite at will.
Tamas Horvath, who led the work at Yale
University, said: “By observing how the
appetite centre of the brain responds to
marijuana, we were able to see what drives
the hunger brought about by cannabis and
how that same mechanism that normally
turns off feeding becomes a driver of
eating. It’s like pressing a car’s brakes and
accelerating instead.”
Scientists have previously shown that
activating a cannabinoid receptor in the
brain, called CB1R, tends to trigger an
increased desire to eat. Until now,
however, it was not known which bits of
the brain’s appetite circuitry were
involved. The latest study tested this in
mice, by injecting cannabinoids into the
brain and monitoring which neurons were
activated in response.
The research, published in Nature,
unexpectedly showed that activity was
boosted in a group of nerve cells called
POMC (pro-opiomelanocortin) neurons,
which normally produce feelings of satiety.“We were surprised to find that the
neurons we thought were responsible for
shutting down eating, were suddenly
being activated and promoting hunger,
even when you are full,” said Horvath. “It
fools the brain’s central feeding system.”
Further investigation showed that the
cannabis “subverted” these neurons,
causing them to release hunger
stimulating chemicals rather than appetite
suppressing chemicals, explaining how the
drug can produce a sudden urgent desire
for a packet of Doritos or a bowl of Coco
Pops.
The scientists speculate that cannabinoids
“flips the switch” on the neurons by
binding to tiny energy-generating
organelles inside the cells, called
mitochondria, in addition to receptors on
the neurons’ surface.
Intriguingly, people who smoke cannabis
regularly do not tend to gain weight – if
anything they are less likely to be obese. It
is not clear whether this is because the
“munchies” effect wears off in people who
smoke regularly, or whether habitual
smokers eat less when not under the
influence of the drug.
The scientists are now exploring whether
the brain circuitry that produces the
“munchies” is also central to the feeling of
being “high”.
Previously, Japanese researchers have
shown that cannabis appears to interact
with taste receptors to enhance the sweet
taste in foods, thus boosting certain
cravings. Other work has shown that mice
given THC (tetrahydrocannabinol), one of
the active ingredients in cannabis, had an
enhanced sense of smell and an overactive
“reward” system, which provides hints to
why some people find eating especially
gratifying when under the influence.
