[KMag]

It's probably best to not think in terms of a binary ADHD diagnosis, but rather on an attention spectrum.

Students low on the attention spectrum (but either just above ADHD diagnosis or without the resources to get diagnosed) are probably more likely to self-medicate.

So, the fact that some students who self-select for self-medication show improvements isn't necessarily evidence that someone in the middle or upper end of the attention spectrum will see improvements. However, it does suggest a need for research into the effects on randomly selected non-ADHD-diagnosed people.