When skeptical New York Times columnist Adam Grant was informed last year, “But Steve Jobs meditated!”, he replied,

Yeah, and he also did L.S.D. — do you want me to try that, too?
He goes on:

I polled a group of meditation researchers, teachers and practitioners on why they recommend it. I liked their answers, but none of them were unique to meditation. Every benefit of the practice can be gained through other activities.
For one thing, mindfulness is a moving target. As a Veterans’ Affairs publication (2014) pointed out,

Evaluations of a large number and variety of mindfulness interventions have been published, there is only limited agreement on how to define mindfulness interventions, and formats and components vary across interventions.
Despite measurement difficulties, traditional spiritual practices, Western as well as Eastern, do “work.” They are not in conflict with science-based psychology. For that matter, there is nothing unique about Eastern meditation. Rosary prayers work just as well for devout Catholics.
That said, mindfulness techniques have been shown to reduce the need for painkillers (reducing damaging side effects for those with chronic disease), help manage healthy glucose levels, and reduce diabetes risks. Consistent with general stress reduction, they help relieve anxiety and low back pain. As noted by The Lancet, mindfulness practice may reduce the need for antidepressants or help prevent relapse into depression. Side effects are rare and minor. In education, mindfulness can help focus attention and improve attentiveness in willing learners. It can reduce the stress of exams, though that doesn’t necessarily improve marks. But some sources may read too much into these research claims. Author and practitioner Arnie Kozak points out at BeliefNet,

… decades of research suggest that setting aside time for mindfulness can improve concentration and reduce stress.” I placed emphasis on “suggest” but this often gets overlooked. This claim may be true but there really isn’t enough evidence to support this with rigorous conviction. Many of the studies included in that claim have not been sufficiently controlled.
A 2014 analysis of 47 medical studies found “no evidence that meditation programs were better than any active treatment (i.e., drugs, exercise and other behavioral therapies).” But those 47 were only three percent of the total (19,000) because most of the terminology and data were not comparable.
That doesn’t mean meditation isn’t helpful; it mainly means that the current craze merits caution. As mindfulness expert Barry Boyce points out, “We’re talking about minds, after all. They’re hard to measure."
So when is mindfulness a bad thing? Meditation was developed as a lifelong practice, says psychotherapist Mary Sykes Wylie:

It was never intended to be a quick-acting mental Ibuprofen/Xanax, but a long-term discipline that increased awareness, resulting in deep insight into the subtleties of existence itself.
Even the terminology of the original languages often defies clarification. Word has begun to surface in recent years about the “dark side” to mindfulness. As Miguel Farias, author of The Buddha Pill, puts it,: “[M]editation, for all its de-stressing and self-development potential, can take you deeper into the recesses of your mind than you may have wished for.” And more than some can handle by themselves.
There is a long history of casual encounters gone wrong, resulting in psychological trauma. That is perhaps the principle danger of heedless use in workplaces and schools. Christina Surawy, a clinical psychologist, warns in the Guardian:

MBCT [Mindfulness-based cognitive therapy] isn’t suitable for patients who are in the grip of a drug or alcohol dependency, as they won’t be able to fully engage with the therapy. Also, patients who are recently bereaved may find MBCT too overwhelming.
Psychologist and meditator Kate Williams offers an appropriate caution:

I am a strong believer in MBIs and can see the benefits it can bring. Yet we must remain ‘mindful’ of how we promote and talk about mindfulness to ensure we carefully promote its use and application to mental or physical health issues whilst in the early days of its research.
A recent article in the Washington Post (April 8, 2016) asks, “When ‘mindful’ is a mayo, a diet, a mantra, does it actually mean anything?” My own reading and research suggests that the answer, in that case, is: Let's hope not!
Mindfulness practices should be treated seriously or left alone. They should be offered in workplaces or schools only as a voluntary activity and not tied to performance.   See also: Part 1: Responding thoughtfully to the mindfulness fad, Part 2: Mindfulness is not a product or service, Part 3: Why pioneers are disillusioned with the “mindfulness” scene even as schools embrace it. Denyse O’Leary is a Canadian journalist, author, and blogger, and co-author of The Spiritual Brain.