Yeah a lot of smokers are picky enough about their weed to give the strains names, such as Acapulco Gold, or One Eyed Jamaican. Growers pride themselves on good weed. It's not like coke meth or heroin where people are extremely addicted and it benefits shady dealers to sell cut product. If weed is cut it'd probably just be cut with a lower quality weed.
Actually there is some shit that some people put in weed to make it look better(for untrained eye) and to add weight. Also i have heard people cutting weed with glass powder and all sorts of other nasty stuff. Not even going to go with what sort of shit people put in hash..
"Where wisdom reigns, there is no conflict between thinking and feeling."
— C.G. Jung
I'm not surprised and for some its pretty low to begin with.
In the UK its been linked with psychosis but I tend to think is that a chicken and egg scenario, after all there are people who are alcoholics or vulnerable to alcohol addictions and never know it until they take a drink of alcohol.
It doesn't seem like the study considered other factors, like whether other substances were abused, demographics, etc... Marijuana use is generally banned or heavily restricted; it's not difficult for me to imagine teenagers who illegally use it regularly lacking qualms about abusing other substances.
Anecdotally, my high school classmates who were "potheads" also frequently used ecstasy, alcohol, or other drugs. The type drug use attracted didn't really care about intellectual pursuits. Also, most of their parents didn't seem very involved, so long as their kids graduated and didn't go to jail. I can see these things potentially affecting IQ, too.
I think that it would be very difficult to conduct a marijuana study- especially one involving adolescents- that made a fair attempt to control the variables among its participants, due to marijuana's legality and stigma. Most marijuana studies I've seen don't even bother to identify potential variables.
i think breathing lowers your iq. quick everyone! stop breathing, oh wait so does that. we're fucked but as well light a dooby and get blazed. I actually smelled weed walking across the parking lot to class i thought hmmm maybe i'd ask to have a hit but i was on my way to a test, so i figure i can't be stoned for that and i smoke so rarely it's not like i'd be remotely functional enough to fill out a scan tron, which are evil when not fucked up.