marjiuana facts:

The Munchies
One peculiar phenomenon associated with marijuana use is the increased hunger that users feel, often called the "munchies." Research shows that marijuana increases food enjoyment and the number of times a person eats each day, according to the National Institutes of Health.
Until recently, the munchies were a relative mystery. However, a recent study by Italian scientists may explain what happens to increase appetite in marijuana users. Molecules called endocannabinoids bind with receptors in the brain and activate hunger.

This research indicates that endocannabinoids in the hypothalamus of the brain activate cannabinoid receptors that are responsible for maintaining food intake. The results of the study were published in an April 2001 issue of the scientific journal Nature.
from howstuffworks.com

The current study (marijuana promotes brain cell growth) focused on a particular formulation of synthetic cannabinoid known as HU210 -- a compound which (Dr. Xiao) Zhang described as the most powerful cannabinoid in the world.

HU-210 is a synthetic cannabinoid that was discovered around 1988 in the group of Dr Raphael Mechoulam at the Hebrew University. HU-210 is 100 to 800 percent more potent than natural THC Tetrahydrocannabinol, also known as THC, from Cannabis and has an extended duration of action. HU-210 is the (+)-1,1-dimethylheptyl analog of 7-hydroxy-delta-6-tetrahydrocannabinol. The abbreviation HU stands for Hebrew University.

Tetrahydrocannabivarin, also known as tetrahydrocannabivarol, THCV, or THV, is a psychoactive cannabinoid found in minor amounts in the hemp plant Cannabis sativa. It is an analog of tetrahydrocannabinol (THC) with the sidechain shortened by two CH2 groups. THCV can be used as a marker compound to differentiate between the consumption of hemp products and synthetic THC (Dronabinol, Marinol).