There are many excuses, and abuses for many legitimate medicines. That does not take away from the fact that they are used effectively by other people for real medical reasons.
The recent study you speak of has many flaws. There are many outside factors that can lower someones IQ score from the 70s, to today. Standards alone can account for IQ score discrepancies. There are thousands of doctors, lawyers, engineers, and other prestigious functional people in society that have, and probably continue to use cannabis.
Just read something today that confirms an already known fact that cannabis has cancer fighting properties. I should note that it is typically not in a high enough concentration when consumed in smoking form. They are more effective in tinctures, typically having high CBD, rather than THC. As most know, THC is the psychoactive component. CBD is one of about 70 cannabinoids that acts as kind of a balancing agent for the psychoactive component. CBD also has been shown to be anti-inflammatory, anti-spasmodic, anti-oxidant, and many other beneficial effects. IMO, that is why the FDA approved synthetic versions of THC fail. They are copying the psychoactive component and ignoring the ones that have proven to be medicinal.
http://www.huffingtonpost.com/2012/09/19/marijuana-and-cancer_n_1898208.html?icid=maing-grid7|maing6|dl2|sec3_lnk1&pLid=207938
There was also a study done that indicated that marijuana only smokers actually had an increased lung capacity over tobacco smokers, as well as non smokers. I think this was more attributed to a technique typically used by MJ smokers to hold in the smoke. Similar to the way divers build up lung capacity.
http://healthland.time.com/2012/01/1...h-lung-damage/
There are studies out there that clearly contradict the FDA's stance of not having medicinal properties. They just ignore them.