The principal metric would be mood, however defined. Zeo’s web interface & data export includes a field for Day Feel, which is a rating 1-5 of general mood & quality of day. I can record a similar metric at the end of each day. 1-5 might be a little crude even with a year of data, so a more sophisticated measure might be in order. The first mood study is paywalled so I’m not sure what they used, but Shiotsuki 2008 used State-Trait of Anxiety Inventory (STAI) and Profiles of Mood States Test (POMS). The full POMS sounds too long to use daily, but the Brief POMS might work. In the original 1987 paper A brief POMS measure of distress for cancer patients, patients answering this questionnaire had a mean total mean of 10.43 (standard deviation 8.87). Is this the best way to measure mood? I’ve asked Seth Roberts; he suggested using a 0-100 scale, but personally, there’s no way I can assess my mood on 0-100. My mood is sufficiently stable (to me) that 0-5 is asking a bit much, even.
One of the other suggested benefits is for boosting serotonin levels; low levels of serotonin are implicated in a number of issues like depression. I’m not yet sure whether tryptophan has helped with motivation or happiness. Trial and error has taught me that it’s a bad idea to take tryptophan in the morning or afternoon, however, even smaller quantities like 0.25g. Like melatonin, the dose-response curve is a U: ~1g is great and induces multiple vivid dreams for me, but ~1.5g leads to an awful night and a headache the next day that was worse, if anything, than melatonin. (One morning I woke up with traces of at least 7 dreams, although I managed to write down only 2. No lucid dreams, though.)
He recommends a 10mg dose, but sublingually. He mentions COLURACETAM’s taste is more akin to that of PRAMIRACETAM than OXIRACETAM, in that it tastes absolutely vile (not a surprise), so it is impossible to double-blind a sublingual administration - even if I knew of an inactive equally-vile-tasting substitute, I’m not sure I would subject myself to it. To compensate for ingesting the coluracetam, it would make sense to double the dose to 20mg (turning the 2g into <100 doses). Whether the effects persist over multiple days is not clear; I’ll assume it does not until someone says it does, since this makes things much easier.
I eventually met Seltzer in an underground food court not far from the Pentagon. He's slim, with a shaved head, and he spoke precisely, rarely stumbling over his words. I asked him if he had any ethical worries about smart drugs. After a pause, he said that he might have a concern if somebody popped a neuroenhancer before taking a licensing exam that certified him as, say, a brain surgeon, and then stopped using the drug. Other than that he couldn't see a problem. He said that he was a firm believer in the idea that "we should have a fair degree of liberty to do with our bodies and our minds as we see fit, so long as it doesn't impinge on the basic rights, liberty and safety of others". He argued: "Why would you want an upward limit on the intellectual capabilities of a human being? And, if you have a very nationalist viewpoint, why wouldn't you want our country to have the advantage over other countries, particularly in what some people call a knowledge-based economy?" He went on: "Think about the complexity of the intellectual tasks that people need to accomplish today. Just trying to understand what Congress is doing is not a simple thing! The complexity of understanding the gamut of scientific and technical and social issues is difficult. If we had a tool that enabled more people to understand the world at a greater level of sophistication, how can we prejudice ourselves against the notion simply because we don't like athletes to do it? To me it doesn't seem like the same question. And it deserves its own debate."
Kratom (Erowid, Reddit) is a tree leaf from Southeast Asia; it’s addictive to some degree (like caffeine and nicotine), and so it is regulated/banned in Thailand, Malaysia, Myanmar, and Bhutan among others - but not the USA. (One might think that kratom’s common use there indicates how very addictive it must be, except it literally grows on trees so it can’t be too hard to get.) Kratom is not particularly well-studied (and what has been studied is not necessarily relevant - I’m not addicted to any opiates!), and it suffers the usual herbal problem of being an endlessly variable food product and not a specific chemical with the fun risks of perhaps being poisonous, but in my reading it doesn’t seem to be particularly dangerous or have serious side-effects.