I have a little bit different view point than the doctors who are advocating meditation.
I don't look at meditation as a kind of medical treatment. I look at it as an exercise for spiritual development. And from my own experience I find that it is best to get your brain running as best you can by all other means first then meditation will have the most effect.
I have had a meditation practice for most of my life and I think meditation can improve your mood.
But I have found that, at lest for me, there are much more important factors that have to come first.
The most important factor for me is diet. If I am not on the right diet, meditation doesn't work. It has no effect. I can't tell you what to eat because everyone is different. I have to avoid starchy and sugary foods and I have to include some amount of poultry or red meat in my diet. Eggs, cheese, and even fish do not provide me with adequate nutrients for my brain to work properly.
A second factor is relaxation. Meditation can be relaxing but so can sleeping. The kind of relaxation I am referring to here is the kind produced by qigong or tai chi or yoga. Once you learn to relax that way, you can approximate it by meditation because part of the effect is produced by breathing the way it is done in those exercises and you can breathe the same way while meditating, but full relaxation also includes relaxing the muscles and you have to do that through movement.
A third factor is the lifestyle you lead. If you lead a stressful lifestyle you are undoing the effects of meditation. I am not saying you should not lead a stressful lifestyle. Different people are here for different reasons. But folks who are interested in meditation should understand that if they come home from a stressful day at work or school and then sit down and meditate, they are going to have to do a lot more to get the same effect than if they led a quiet secluded lifestyle. There is a reason Buddhist monks live like monks. I am not advocating living like a monk, I just think that people ought to understand and have realistic expectations. (People who do lead a stressful life might benefit from doing qigong, tai-chi, or yoga to help relax and quiet the mind before trying to meditate.)
I know someone who suffers from periods of depression. She has become very cynical about medicine in this area because it seems to have followed a long string of fads including:
Cognitive Behavioural Therapy
What this suggests to me, is that nothing they do in this area works much, but all are boosted by the placebo effect for a while. This of course makes entirely good sense if science really knows very little about the nature of mind.
I suspect the effectiveness of meditation may depend on whether they dilute the philosophy behind mindfulness in the process of pulling it into the medical system.
However, I have never been depressed, and haven't meditated except for small experiments on my own that weren't terribly successful.