Even people who don't smoke dope get the munchies.
Cannabis-like molecules circulating in the brain, that occur naturally in the body of even the most upright citizen, spark hunger pangs and may contribute to obesity, says New Scientist magazine.
Known as cannabis receptors or cannabinoids, they could be the missing link in
solving the puzzle of why some people eat more than others.
Dr George Kunos and a team of researchers at Virginia Commonwealth University in Richmond, Virginia, found the absence of cannabis receptors in the brain made mice much less hungry.
It has been known for some time that a hormone called leptin tones down hunger, but the reasons leptin works remain a puzzle.
Dr Kunos found that injecting leptin into rats and mice automatically led to a sharp drop in cannabinoid levels.
Normally, mice that have been starved eat voraciously when finally given something to eat.
Dr Kunos found that the absence of cannabis receptors changed their habits.
Genetically modified mice lacking the receptors ate far less food than usual after being starved for 18 hours.
Unmodified mice, given drugs to block the cannabis receptors, also ate much less.
In a finding that could link cannabinoids to human obesity, Dr Kunos and his team also found high levels of cannabis-like substances in the brains of excessively fat mice. The mice were born with a genetic defect that prevented them from making leptin.
Leptin's role as an appetite "off-switch" has been known since the 1990s.
Cannabinoids could be the missing part of the puzzle.
So, could too much natural cannabinoid - as opposed to the inhaled kind - in the brain make people fat?
"It's reasonable to speculate that it contributes to some forms of obesity," Dr Kunos said.
The research backs up work by scientists at the Hebrew University in Israel, who found that injecting newborn mice with drugs that neutralised the effects of cannabis dramatically suppressed their appetite - so much so that they stopped suckling and died.
In France, scientists are giving obese people an experimental drug designed to block cannabinoid receptors.
In a trial lasting 16 weeks, a compound was given to patients to see if it curbed their hunger.
Early results indicated the patients given the compound lost more weight than the control group.
