Caffeine metabolism is primarily determined by the cytochrome enzyme P-450 1A2 (CYP1A2), and studies have shown that different ethnic populations exhibit widely varying expressions of the gene responsible for CYP1A2. Evidence suggests that a particular CYP1A2 impacts caffeine consumption by modifying the risks of certain diseases that are associated with caffeine consumption. It has also been shown that variations in the expression of genes that code for adenosine and dopamine receptors play a role in mediating your response to caffeine. For example, in Caucasians, the presence of certain genetic expressions for both adenosine and dopamine receptors is associated with caffeine-induced anxiety. Variations in CYP1A2 are also responsible for the speed at which different people metabolize caffeine.

One might suggest just going to the gym or doing other activities which may increase endogenous testosterone secretion. This would be unsatisfying to me as it introduces confounds: the exercise may be doing all the work in any observed effect, and certainly can’t be blinded. And blinding is especially important because the 2011 review discusses how some studies report that the famed influence of testosterone on aggression (eg. Wedrifid’s anecdote above) is a placebo effect caused by the folk wisdom that testosterone causes aggression & rage!

Taking the tryptophan is fairly difficult. The powder as supplied by Bulk Nutrition is extraordinarily dry and fine; it seems to be positively hydrophobic. The first time I tried to swallow a teaspoon, I nearly coughed it out - the power had seemed to explode in my mouth and go down my lungs. Thenceforth I made sure to have a mouth of water first. After a while, I took a different tack: I mixed in as much Hericium as would fit in the container. The mushroom powder is wetter and chunkier than the tryptophan, and seems to reduce the problem. Combining the mix with chunks of melatonin inside a pill works even better.

Avocados. Avocados are almost as good as blueberries in promoting brain health, says Pratt. "I don't think the avocado gets its due," agrees Kulze. True, the avocado is a fatty fruit, but, says Kulze, it's a monounsaturated fat, which contributes to healthy blood flow. "And healthy blood flow means a healthy brain," she says. Avocados also lower blood pressure, says Pratt, and as hypertension is a risk factor for the decline in cognitive abilities, a lower blood pressure should promote brain health. Avocados are high in calories, however, so Kulze suggests adding just 1/4 to 1/2 of an avocado to one daily meal as a side dish.

That's been my experience with this product, just trying to get it to work. Some days, I may get lucky and feel very alert even with no sleep, other days it does nothing. By three stars, I mean more of an average rating, not that I didn't like it. It just didn't work as well as advertised. But everyone's body is different, so you have to take these under various conditions to see what works for you. I may buy some more and update my review later since I'm finding the right pattern to making the pills work, and to see if it works better in autumn/winter. Remember to take breaks with these too, it's quite a bit of vitamins and minerals to take everyday.
Amphetamine – systematic reviews and meta-analyses report that low-dose amphetamine improved cognitive functions (e.g., inhibitory control, episodic memory, working memory, and aspects of attention) in healthy people, and in individuals with ADHD.[21][22][23][25] A 2014 systematic review noted that low doses of amphetamine also improved memory consolidation, in turn leading to improved recall of information in non-ADHD youth.[23] It also improved task saliency (motivation to perform a task) and performance on tedious tasks that required a high degree of effort.[22][24][25]