If you’ve ever wrestled your way through bouts of depression or anxiety, you’ve likely been given the suggestion of “writing in a gratitude journal.” The practice is ubiquitous; people take a pen and a journal at some point each day and write down one thing or a number of things they feel grateful for.

The first question — a logical one at that from the perspective of somebody fighting depression — might be “How will writing about being grateful when I’m already unhappy, magically make me happy?” As it turns out, there’s no magic to the practice at all. It’s a method that science has found to be quite effective in battling depression.

First, gratitude journaling works when put into consistent practice. Over time, it slowly changes one’s perception of their given circumstances and eventually, new challenges and hardships are met with newfound positivity because we’ve been slowly changing our perceptions of such things ahead of time.

In a study conducted by Greater Good Magazine, 300 participants were observed at a university. Most of the subjects were people with already low reported levels of mental health and many were due to receive some kind of mental health counseling in their school environments. When participants wrote letters of gratitude throughout their counseling, they later reported higher levels of mental health and happiness as long as 12 weeks after counseling had stopped than subjects who were writing, but not specifically practicing “gratitude journaling.”

In comparing the actual letters of both groups, researchers looked at the number and frequency of positive emotion words versus negative emotion words as well as the prominence of the word “we.” In this case, it wasn’t the simple practice of gratitude journaling that seemed to have the heaviest impact but actually the absence of negative emotion words that seemed to explain the mental health gap between the groups. The finding here suggests that gratitude journaling simply takes our focus away from negative influences more than it manufactures happiness.

The study noted that, as mentioned earlier, the effects were only prominent over time and not the results of a one-off task. In fact, the mental health levels didn’t seem to differ amongst groups one week after the writing activities, rather it wasn’t until four weeks after the practice finished that mental health levels started to differ and those gaps became even larger (and healthier) 12 weeks later. The interesting note about that finding is that the mental health benefits of most positive activities have a decreasing effect and impact over time. Somehow, this particular journaling practice is unique. While the study didn’t pinpoint an exact reason for this rogue snowballing effect, it was still an important key to understanding that the benefits of gratitude journaling can’t take place in just a week or maybe even a few weeks. Sometimes it can be months before the practice starts to have a real impact, but as far as science is concerned, it works. Just make sure you stay disciplined, committed, and patient while waiting for the benefits of gratitude journaling to kick in.