Difficulty concentrating.  As mentioned previously, this may not be a direct result of age—though it can be a common side-effect of struggling with fatigue and brain fog.  When it takes more mental energy to think, it is harder to stay with it for a long time.  Many of us also are surrounded by distractions clambering for our limited attention.  Modern life is fast-paced, stressful, and overcrowded.
Take the synthetic nootropic piracetam, for example. Since piracetam has been shown to improve cell membrane function and cause a host of neuroprotective effects, when combined with other cell membrane stabilizing supplements such as choline and DHA, the brain cells on piracetam can better signal and relay messages to each other for a longer period of time, which improves cognition and brain activity and decreases risk of a crash. So one example of an intelligent “stack” is piracetam taken with choline and DHA.
That it is somewhat valuable is clear if we consider it under another guise. Imagine you received the same salary you do, but paid every day. Accounting systems would incur considerable costs handling daily payments, since they would be making so many more and so much smaller payments, and they would have to know instantly whether you showed up to work that day and all sorts of other details, and the recipients themselves would waste time dealing with all these checks or looking through all the deposits to their account, and any errors would be that much harder to track down. (And conversely, expensive payday loans are strong evidence that for poor people, a bi-weekly payment is much too infrequent.) One might draw a comparison to batching or buffers in computers: by letting data pile up in buffers, the computer can then deal with them in one batch, amortizing overhead over many items rather than incurring the overhead again and again. The downside, of course, is that latency will suffer and performance may drop based on that or the items becoming outdated & useless. The right trade-off will depend on the specifics; one would not expect random buffer-sizes to be optimal, but one would have to test and see what works best.

But like any other supplement, there are some safety concerns negative studies like Fish oil fails to hold off heart arrhythmia or other reports cast doubt on a protective effect against dementia or Fish Oil Use in Pregnancy Didn’t Make Babies Smart (WSJ) (an early promise but one that faded a bit later) or …Supplementation with DHA compared with placebo did not slow the rate of cognitive and functional decline in patients with mild to moderate Alzheimer disease..

Artichoke + Forskolin: There is plenty of evidence that suggests artichoke extract supplements (made from the leaves of artichokes) offer strong neural antioxidant properties. Additionally, Forskolin (Coleus forskohlii) is one of the few studied compounds known to naturally boost cAMP (Cyclic Adenosine Monophosphate) in your brain and is also important for neural signaling within brain cells (291m 292). I’ve experienced noticeably enhanced memory and word recall when consuming this combo. Tim Ferriss talked about this one a bit in my podcast with him, particularly referencing its presence in the somewhat popular cognition supplement “CILTEP”. Made primarily from artichoke extracts and forskolin, CILTEP is a stack that also contains vitamin B6, L-phenylalanine and acetyl-L-carnitine.  It is recommended to take two to three capsules at the beginning of each day and to skip dosage one or two days per week to achieve optimal results.
3 days later, I’m fairly miserable (slept poorly, had a hair-raising incident, and a big project was not received as well as I had hoped), so well before dinner (and after a nap) I brew up 2 wooden-spoons of Malaysia Green (olive-color dust). I drank it down; tasted slightly better than the first. I was feeling better after the nap, and the kratom didn’t seem to change that.

Nootropics still exist largely in an unregulated gray area, which makes users somewhat hesitant to discuss their regimens. But I did speak to several people who told tales of increased productivity and sharpened focus. Bob Carter, a financial analyst for a start-up called LendingHome, says that nootropics have replaced his other morning stimulant. “I basically think of it as a substitute for coffee,” he says. “I think the problem with a cappuccino from Starbucks is that it gives you the feeling of being jittery. Whereas with this particular supplement, I feel more calm.”

In avoiding experimenting with more Russian Noopept pills and using instead the easily-purchased powder form of Noopept, there are two opposing considerations: Russian Noopept is reportedly the best, so we might expect anything I buy online to be weaker or impure or inferior somehow and the effect size smaller than in the pilot experiment; but by buying my own supply & using powder I can double or triple the dose to 20mg or 30mg (to compensate for the original under-dosing of 10mg) and so the effect size larger than in the pilot experiment.

Here’s a thing or two you should know about your brain, so you can have a better understanding of natural brain supplements. This is the most important organ in our body that controls every single action we take. On the other hand, this importance comes at the huge price for our body’s energy levels. Our brain usually requires up to 20% of the body’s energy to function properly. The energy consumption can easily rise above 60%, if your brain engages in a series of intense mental activities.
So the chi-squared believes there is a statistically-significant difference, the two-sample test disagrees, and the binomial also disagrees. Since I regarded it as a dubious theory, can’t see a difference, and the binomial seems like the most appropriate test, I conclude that several months of 1mg iodine did not change my eye color. (As a final test, when I posted the results on the Longecity forum where people were claiming the eye color change, I swapped the labels on the photos to see if anyone would claim something along the lines when I look at the photos, I can see a difference!. I thought someone might do that, which would be a damning demonstration of their biases & wishful thinking, but no one did.)
According to the US Food and Drug Administration, "Piracetam is not a vitamin, mineral, amino acid, herb or other botanical, or dietary substance for use by man to supplement the diet by increasing the total dietary intake. Further, piracetam is not a concentrate, metabolite, constituent, extract or combination of any such dietary ingredient. [...] Accordingly, these products are drugs, under section 201(g)(1)(C) of the Act, 21 U.S.C. § 321(g)(1)(C), because they are not foods and they are intended to affect the structure or any function of the body. Moreover, these products are new drugs as defined by section 201(p) of the Act, 21 U.S.C. § 321(p), because they are not generally recognized as safe and effective for use under the conditions prescribed, recommended, or suggested in their labeling."[33]
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