IQ drop can correlate with how that person was feeling that day. The tests used to test IQ not only rate a particular type of intelligence but also require the person being tested to be able to fully concentrate. Meds or not I perform better when I'm well rested and engaged. My "IQ" would drop on days I'm feeling medicated, PMSing, tired from lack of sleep or dissociative.
There's a danger to reading the results or someone's interpretation of the study without looking at the complete study. Firstly, you can't see the control measures nor can you see the researchers evaluation of factors they could not control - such as how well rested a participant was.
Also, the factors involved in the brain density experiment. What was the control group? How did they manage outside influences or things they could not control. Did they check if there was evidence of an undiagnosed condition? Etc etc
The brain also has ways to compensate for damage. If you look at brain imagining in eating disorders or PTSD for instance, there is considerable difference between those scans and scans of healthy brains. But when recovery happens, the brains of those with the illness return to normal. This is something we've only learnt in the last decade. Before then we believed that eating disorders caused permanent change. Or were that way before onset of disorder. We've also learnt in the last decade that DNA is not completely fixed.
Basically, it takes years to understand something so I wouldn't base your decisions on a couple of studies