I know that there is a lot of research going into transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS).
For some diseases it has been shown to be effective.
However, for ADHD - as far as i can see - the studies don't agree and it is preliminary for any conclusions [1].
From [1]:
Finally, a PubMed search (keywords: tDCS AND attention-deficit hyperactivity disorder) identified 24 papers, including 2 original clinical studies (single-session studies) and 80 patients. One study (60 patients) did not find significant differences between active and sham tDCS regarding the effect of bihemispheric tDCS of the DLFPC (left anode + right cathode) on behavioral performance in go/no-go tasks (Cosmo et al., 2015). Conversely, the other study (20 patients) showed that anodal tDCS of the left DLPFC (with right supraorbital cathode) increased the proportion of correct responses in go/no-go tasks, whereas cathodal tDCS of the left DLPFC increased the inhibition accuracy (Soltaninejad et al., 2016). Obviously, reported results are too preliminary to make any recommendation for the use of tDCS in all these psychiatric conditions.
Maybe you can tell him that and also tell him that I am quite interested in the device to check if it can reduce my heart palpitations!