Study: High-potency marijuana linked with neural damage

"We found that frequent use of high-potency cannabis significantly affects the structure of white matter fibres in the brain, whether you have psychosis or not," 
The main psychoactive ingredient in weed, tetrahydrocannabinol (THC), is much more concentrated in modern skunk strains as compared to traditional pot and hash -- up 14 percent as compared to 4 percent.