Kelly McGonigal from Stanford or Harvard argues that it increases willpower, but so does just doing things.
There was a study showing Transcendental meditation decreases blood pressure, but Transcendental meditation is a gimmick and the study was funded by the people pushing the system, etc.
All the Harvard studies about core temperature increases show that the monks are actively contracting their muscles to achieve the effect. Same story with slowing down heart-rate. Neither of which ever achieves out-of-norm ranges.
Oh, and good ideas come to me while I am trying not to focus on anything. Almost like the mind is trying to find an excuse to break single-point attention.
edit: Also, meditation traditions are found all over the world - for example a Christian mystic, Teresa of Avila meditated all the time.
edit 2 in reply to below: Sure, semantics, but you are definitely right to some degree. The difference is that the mechanism behind relaxation is clear.
Isn't that a form of meditation too?
Source? TM is just vedic (mantra) meditation.
edit: Editing because I really do want to understand - the mantras serve no purpose as far as I can tell. There is no reason why you can't focus on "I am a good boy today" rather than something in Hindi. It's just a chant, and trying to teach a "special personalized" chant and charge for it as dishonest.
edit 2 to reply to the post below (can't post so much in one thread): Sure, it's not a source, but it explains the logic of why it's a gimmick.
edit 3: @sol: And this makes some sort of sense to you? You claim to understand the mechanism behind this or that someone who made up a random phrase for money does?
I know someone whose lupus went into remission after they started chanting, but there was one very particular chant that they found working for them.
TM does charge a fee, which I found reasonable for 90 minutes of 1-on-1 instruction, 4 evenings of classes, and lifetime access to any TM center worldwide. They also have a sliding scale and many opportunities for scholarships. They will tell you that 1-on-1 instruction is integral to the learning process. I did mindfulness meditation for 3 years before switching to TM, and the value I got from the instruction was to simplify my natural tendency to over-complicate these processes (don't think, do). The instruction was absolutely necessary for me, but it very likely would not be necessary for a subset of people.
I understand the inclination to dismiss it as a pyramid scheme or a cult, as the latter was my hangup to trying TM sooner. My opinion: if it is a cult, then it's a bottom-up cult (in that the source of its cult-ness is the obsession of the followers, rather than as the intent from the top). This is very similar to my experience at a Tony Robbins 4 day event; the two days with Robbins were life-changing and _phenomenal_, but the days without him were so bad that I walked out. I tried talking to other attendees about the qualitative difference, but literally nobody was having it, and some of them even got aggressive with me. However off-putting bad sessions and rabid followers may be, it does not change the efficacy, meaning, and power of the experience I had.
TM has a free 90-minute class that I encourage everyone to check out, once we're out of this mess.
While I have not tried Transcendental Meditation, I do have some knowledge of the fundamental notions of Buddha's teaching and would say that meditating on compassion over and over again until you weep for all sentient beings is essential to eliminating the hard shell of the intellect that keeps us from being receptive and sensitive to the abiding nature of reality.
In a similar way, you can consider one mushroom and its limited awareness of the forest. If the mushroom were to contemplate a compassionate wish for other mushrooms, the identity-difference would dissolve and the mushroom could become aware of the whole forest floor. Just a simple metaphor, but perhaps the image is clear.
Meditating can sharpen your focus, but meditation cannot take you all the way there without knowledge of the way things are in a phenomenological sense.
So if you need a recommended regimen, start with compassion and when your compassion is strong ponder identitylessness and interdependence.
Pray to find the perfect resources and they will find you.