A priori you might think there is is a high likelihood that the drug use will just make everything worse.
That is precisely the bias and weakness of this study. Self-medication is almost always a red flag; why not do it in a context of other people that know their stuff, be it tradition, institution (therapy) or even close friends that are mutually invested in each other's long term well-being? DIY approaches to self-transformation are fragile; no one to hold you out of potential pitfalls, to protect you from re-traumatization, to call you out on your self-deception.
The title of the article that it "reduces depressive symptoms" is also telling of this bias. If symptom reduction was equivocal to enduring transformation, weed, cocaine and alcohol would have already healed the entire world. Without the study measuring if the subjects transformed their lives in a way that they were equally symptom free for the next 6 months, 1 year, 5 years, we can't conclude anything curative really took place.
Don't get me wrong, they make a theoretical link to ACT in which experiencing of chronically difficult emotions are facilitated, which does offer potentially huge benefits, but just like we don't use studies on antidepressants that show symptom reduction to go shop bunch of prozac, we shouldn't readily assume we can use this one to facilitate our own healing in a DIY fashion either.
you select a sample of people who want to get better, and are surprised they get better more frequently than a group including people who don't? where's the test on a person depressed and not actively trying to get better taking the same drug? i bet the negative side effects and the death of extra brain cells makes it worse.
yes, if someone tries to use drugs to fix something, you absolutely should stop them. there's a reason you need a doctorate to prescribe those drugs.
new test. my test. I'm going to prove wikipedia makes you a neurosurgeon. let's take 300 highschool seniors who read a wiki article on neurosurgery. let's take another 300 from a random sampling at the dmv. send them all to school for neurosurgery. wow. just wow. the 300 who read the article - a higher percentage of them succeeded in becoming a neurosurgeon. holy crap. wikipedia is amazing.