“We didn’t see significant long-term effects from the dosage used,” said Wen-Jun Gao, a professor of neurobiology at the Drexel University College of Medicine, and one of the authors of the study. He added that the brain doesn’t fully stop developing until age 25 or 30, making cognitive enhancement potentially risky even for users who are well into adulthood.

Some people are concerned that when they discontinue the use of nootropics, they will experience cognitive functioning below that of their normal level; however, this is usually not the case, especially regarding nootropics in the racetam class. Discontinuing nootropics will cause a person to lose any benefits experienced on these drugs. In other words, nootropics do not appear to build up the brain in any long-lasting way; their benefits are directly tied to their use. There is no evidence that nootropics erode one’s natural level of cognitive functioning.
I have no particularly compelling story for why this might be a correlation and not causation. It could be placebo, but I wasn’t expecting that. It could be selection effect (days on which I bothered to use the annoying LED set are better days) but then I’d expect the off-days to be below-average and compared to the 2 years of trendline before, there doesn’t seem like much of a fall.
We’d want 53 pairs, but Fitzgerald 2012’s experimental design called for 32 weeks of supplementation for a single pair of before-after tests - so that’d be 1664 weeks or ~54 months or ~4.5 years! We can try to adjust it downwards with shorter blocks allowing more frequent testing; but problematically, iodine is stored in the thyroid and can apparently linger elsewhere - many of the cited studies used intramuscular injections of iodized oil (as opposed to iodized salt or kelp supplements) because this ensured an adequate supply for months or years with no further compliance by the subjects. If the effects are that long-lasting, it may be worthless to try shorter blocks than ~32 weeks.
The use of prescription stimulants is especially prevalent among students.[9] Surveys suggest that 0.7–4.5% of German students have used cognitive enhancers in their lifetime.[10][11][12] Stimulants such as dimethylamylamine and methylphenidate are used on college campuses and by younger groups.[13] Based upon studies of self-reported illicit stimulant use, 5–35% of college students use diverted ADHD stimulants, which are primarily intended for performance enhancement rather than as recreational drugs.[14][15][16] Several factors positively and negatively influence an individual's willingness to use a drug for the purpose of enhancing cognitive performance. Among them are personal characteristics, drug characteristics, and characteristics of the social context.[10][11][17][18]