POT: Cannabis isn't as harmless as suggested

My wife and I often debate on the harmlessness of marijuana. Today, I found this information fixed to my studio monitor.

From USA WEEKEND Sept. 16-18, 2005

Cannabis is the most widely used illicit drug in the United States. Two recent studies show that cannabis damages the vessels in your brain by constricting blood flow - putting you at risk for stroke.

It makes no difference whether you smoke it, eat it or take a pill. The active ingredient tetrahydrocannabinol (THC) is the culprit. The stronger it's concetration - ranging from 1% in some herbal preparations to 65% in some hashish oils - the greater the danger.

Long-term and heavy users are at risk.

Cannabis has long been associated with harmful changes in the brain; now sophoisticated medical tools can pinpoint them. One study demonstrates that impairment of the brain's blood flow persists for at least a month after the last high. This eventually can lead to a stroke and its resulting paralysis, and problems with vision, memory and speech.

well....

I'm at a loss for an argument. anybody?