So reading the study it is less about cannabis actually affecting the ringing in your ears and more about treating the negative impacts of tinnitus on your life. Yes it doesn't make the ringing in your ears go away but neither does any other treatment method. This is a study on whether or not cannabis would be an effective method to treat the symptoms and results of tinnitus not whether it cures it.

Anxiety and depression are extremely common things that go along with tinnitus. If you don't have tinnitus imagine it being something similar to the times you suddenly become very conscious of your tongue in your mouth or when you become conscious of your breathing. It's something that is there all the time but how heavily it impacts you varies. Sometimes it doesn't bother us at all and we can almost tune it out. Other times, such as when my anxiety is flaring, it becomes deafening and makes it impossible to concentrate. This winds up compounding on my anxiety more often than not and the negative feedback loop can be devastating.

Cannabis has been shown to help with anxiety for many but for some it makes their anxiety worse and creates paranoia. Even this effect can generally be lessened with a different strain or delivery method but there are a rare few who find no help with any strain or delivery method.

Anecdote time:

For me personally the positive effects depend on strain and dosage. Sativas tend to make me paranoid in higher dosages and that paranoia starts those seeds of anxiety which usually starts that negative feedback loop and my tinnitus deafens me and I start to get paranoid about whether or not it's just quiet or if I lost bunch of sounds that I'm supposed to be hearing to the ringing. If I avoid that specific scenario then it generally helps curb the anxiety and helps take the focus away from the ringing. It's not a cure but I also haven't seen a need to seek out a more effective treatment either.