Roll 'em up — in the name of science. A new Michigan State University study recently found that a chemical present in marijuana may be able to slow mental decline in HIV patients. Nearly 50 percent of HIV patients experience a decrease in cognitive ability over time due to the fact that the virus attacks the human immune system, sometimes causing "chronic inflammation" in the brain, the researchers wrote. The lead author of the study, Norbert Kaminski, and his co-author, Mike Rizzo, discovered that chemical compounds in THC — formally known as tetrahydrocannabinol — reduced the number of inflamed white blood cells present in HIV patients.