"According to presented descriptive results, all the studies (100%) showed improvement of ADHD [attention-deficit hyperactivity disorder] symptoms."
That was the standout sentence derived from the findings reported by Hélène Poissant and colleagues  who looked at "the available literature concerning MBIs [mindfulness-based interventions] in adult participants with ADHD." Mindfulness by the way, is described as a way of "reconnecting with our bodies and the sensations they experience" with a specific focus on "an awareness of our thoughts and feelings as they happen moment to moment." I'm no expert on mindfulness or mindfulness-based interventions but, from what I gather, the core of such intervention(s) is based around "somatically focused meditative techniques (body scan, sitting meditation, and mindful yoga) that are thought to help participants cultivate nonjudgmental, mindful awareness of present-moment experience." 'Focusing in on the present' seems to be the phrase that springs to mind.
Poissant et al examined the relevant peer-reviewed science on the application of the MBIs to ADHD upto June 2018. They specifically focused on adults with ADHD, and were able to track down "13 studies conducted with 753 adults (mean age of 35.1 years)" for inclusion in their systematic review. They observed that: "All the studies (100%) showed improvement of ADHD symptoms following an MBI." They also mentioned that: "mindfulness meditation training improves some aspects of executive function and emotion dysregulation" as per the findings of some of those studies.
Despite the '100% of studies showing improvement in ADHD symptoms' sentiments, I'm not falling hook, line and sinker for the value of MBIs in relation to ADHD. The main reason is the high risk of bias identified in quite a few of the studies reviewed by Poissant, related to things like performance bias ("blinding of participants and of personnel") and selection bias ("allocation concealment" and "selection bias"). One could argue that the examination of something like MBIs under research conditions is never going to be perfect. Unlike scientific investigation of a medicine, where a placebo can be formulated to look, smell and taste the same, it would be difficult to come up with something to approximate MBI and indeed, approximate what the 'active ingredient' of mindfulness actually is. Similar issues have been talked about on other occasions on this blog (see here).
That all being said, there is something appealing about MBIs both in terms of effect and also the fact that it can be learned by pretty much anyone, is cost-free and probably about as side-effect free as one could get. If such a simple technique helps with any one of the symptoms of ADHD and improves quality of life for those with ADHD, it's got to be something to be considered alongside the myriad of other possible interventions (see here and see here and see here) that *might* offset the risks that follow a diagnosis of ADHD (see here).
Oh, and it appears that mindfulness and ADHD is a topic in the ascendancy ...
 Poissant H. et al. Behavioral and Cognitive Impacts of Mindfulness-Based Interventions on Adults with Attention-Deficit Hyperactivity Disorder: A Systematic Review. Behav Neurol. 2019;2019:5682050.
 Xue J. et al. A meta-analytic investigation of the impact of mindfulness-based interventions on ADHD symptoms. Medicine (Baltimore). 2019 Jun;98(23):e15957.