I believe this is a topic that many care about. I've tried to find scientific view and here's what I found. The contents below is from the study of James Ahn, Hyung Seok Ahn, Jae Hoon Cheong, and Ike dela Peña on natural product-derived treatment on ADHD, published in Feb, 2016.
Pycnogenol® (French Maritime Pine Bark Extract)
Pycnogenol is a standardized extract derived from the bark of the French maritime pine (Pinus pinaster). This extract is rich in catechin, phenolic acids, procyanidins, and taxifolin, each with multiple biologic effects. Several studies on Pycnogenol showed its potentiality in improving ADHD symptoms in patients. Most notably, a double-blind, placebo-controlled trial with 61 participants (ages 6–14 years) reported that Pycnogenol treatment (1 mg/kg/day) for 1 month alleviated ADHD symptoms, particularly episodic hyperactivity and inattentiveness, and improved visual-motor coordination. One month after termination of Pycnogenol, there was a relapse of symptoms in ADHD participants. The latter study also assumed that Pycnogenol's therapeutic benefits were mediated via an increase in nitric oxide production, which modulates dopamine and norepinephrine release and intake. Pycnogenol reportedly produced mild side effects such as gastric discomfort. Nevertheless, the relatively small number of participants treated with Pycnogenol and the short duration of the study limit the generalization of the study's findings. It is noteworthy, however, that significant effects of Pycnogenol were observed, coupled with minimal side effects, supporting the suggestion that it could be used as an alternative ADHD treatment.
Another randomized, placebo-controlled study investigating efficacy of Pycnogenol reported improvement in attention along with reduction in oxidative DNA damage and normalization of homeostatic antioxidant status in ADHD patients treated for 1 month with the compound. A month after Pycnogenol treatment, the total antioxidant status (TAS) was increased in ADHD children (ADHD children showed lower TAS levels at the beginning of the study compared with healthy controls) and was significantly elevated after 1 month of termination of Pycnogenol treatment. Oxidative stress is believed to be a contributing factor to the etiology of ADHD. The improvement of ADHD symptoms in ADHD patients given Pycnogenol has been attributed to the drug's potent antioxidant effects. Some ancillary benefits of Pycnogenol were normalization of the concentration of urinary catecholamines in children with ADHD and improvement in cerebral blood flow to regions of the brain implicated in this disorder. Of note, neither Pycnogenol nor the positive control, methylphenidate, outperformed placebo on any ADHD rating scale. In summary, Pycnogenol is a promising botanical alternative in the management of ADHD symptoms, although more studies are required before it can be used as an ADHD treatment.