Power-wise, the effects of testosterone are generally reported to be strong and unmistakable. Even a short experiment should work. I would want to measure DNB scores & Mnemosyne review averages as usual, to verify no gross mental deficits; the important measures would be physical activity, so either pedometer or miles on treadmill, and general productivity/mood. The former 2 variables should remain the same or increase, and the latter 2 should increase.
The soft gels are very small; one needs to be a bit careful - Vitamin D is fat-soluble and overdose starts in the range of 70,000 IU35, so it would take at least 14 pills, and it’s unclear where problems start with chronic use. Vitamin D, like many supplements, follows a U-shaped response curve (see also Melamed et al 2008 and Durup et al 2012) - too much can be quite as bad as too little. Too little, though, is likely very bad. The previously cited studies with high acute doses worked out to <1,000 IU a day, so they may reassure us about the risks of a large acute dose but not tell us much about smaller chronic doses; the mortality increases due to too-high blood levels begin at ~140nmol/l and reading anecdotes online suggest that 5k IU daily doses tend to put people well below that (around 70-100nmol/l). I probably should get a blood test to be sure, but I have something of a needle phobia.
Because smart drugs like modafinil, nicotine, and Adderall come with drawbacks, I developed my own line of nootropics, including Forbose and SmartMode, that’s safe, widely available, and doesn’t require a prescription. Forskolin, found in Forbose, has been a part of Indian Ayurvedic medicine for thousands of years. In addition to being fun to say, forskolin increases cyclic adenosine monophosphate (cAMP), a molecule essential to learning and memory formation. 
Before you try nootropics, I suggest you start with the basics: get rid of the things in your diet and life that reduce cognitive performance first. That is easiest. Then, add in energizers like Brain Octane and clean up your diet. Then, go for the herbals and the natural nootropics. Use the pharmaceuticals selectively only after you’ve figured out your basics.
From its online reputation and product presentation to our own product run, Synagen IQ smacks of mediocre performance. A complete list of ingredients could have been convincing and decent, but the lack of information paired with the potential for side effects are enough for beginners to old-timers in nootropic use to shy away and opt for more trusted and reputable brands. There is plenty that needs to be done to uplift the brand and improve its overall ranking in the widely competitive industry. Learn More...
Null results are generally less likely to be published. Consistent with the operation of such a bias in the present literature, the null results found in our survey were invariably included in articles reporting the results of multiple tasks or multiple measures of a single task; published single-task studies with exclusively behavioral measures all found enhancement. This suggests that some single-task studies with null results have gone unreported. The present mixed results are consistent with those of other recent reviews that included data from normal subjects, using more limited sets of tasks or medications (Advokat, 2010; Chamberlain et al., 2010; Repantis, Schlattmann, Laisney, & Heuser, 2010).
I do recommend a few things, like modafinil or melatonin, to many adults, albeit with misgivings about any attempt to generalize like that. (It’s also often a good idea to get powders, see the appendix.) Some of those people are helped; some have told me that they tried and the suggestion did little or nothing. I view nootropics as akin to a biological lottery; one good discovery pays for all. I forge on in the hopes of further striking gold in my particular biology. Your mileage will vary. All you have to do, all you can do is to just try it. Most of my experiences were in my 20s as a right-handed 5’11 white male weighing 190-220lbs, fitness varying over time from not-so-fit to fairly fit. In rough order of personal effectiveness weighted by costs+side-effects, I rank them as follows:
The nonmedical use of substances—often dubbed smart drugs—to increase memory or concentration is known as pharmacological cognitive enhancement (PCE), and it rose in all 15 nations included in the survey. The study looked at prescription medications such as Adderall and Ritalin—prescribed medically to treat attention deficit hyperactivity disorder (ADHD)—as well as the sleep-disorder medication modafinil and illegal stimulants such as cocaine.
Depending on where you live, some nootropics may not be sold over the counter, but they are usually available online. The law regarding nootropics can vary massively around the world, so be sure to do your homework before you purchase something for the first time. Be particularly cautious when importing smart drugs, because quality control and regulations abroad are not always as stringent as they are in the US. Do not put your health at risk if all you are trying to do is gain an edge in a competitive sport.
Bought 5,000 IU soft-gels of Vitamin D-333 (Examine.com; FDA adverse events) because I was feeling very apathetic in January 2011 and not getting much done, even slacking on regular habits like Mnemosyne spaced repetition review or dual n-back or my Wikipedia watchlist. Introspecting, I was reminded of depression & dysthymia & seasonal affective disorder.
Took random pill at 2:02 PM. Went to lunch half an hour afterwards, talked until 4 - more outgoing than my usual self. I continued to be pretty energetic despite not taking my caffeine+piracetam pills, and though it’s now 12:30 AM and I listened to TAM YouTube videos all day while reading, I feel pretty energetic and am reviewing Mnemosyne cards. I am pretty confident the pill today was Adderall. Hard to believe placebo effect could do this much for this long or that normal variation would account for this. I’d say 90% confidence it was Adderall. I do some more Mnemosyne, typing practice, and reading in a Montaigne book, and finally get tired and go to bed around 1:30 AM or so. I check the baggie when I wake up the next morning, and sure enough, it had been an Adderall pill. That makes me 1 for 2.
One thing to notice is that the default case matters a lot. This asymmetry is because you switch decisions in different possible worlds - when you would take Adderall but stop you’re in the world where Adderall doesn’t work, and when you wouldn’t take Adderall but do you’re in the world where Adderall does work (in the perfect information case, at least). One of the ways you can visualize this is that you don’t penalize tests for giving you true negative information, and you reward them for giving you true positive information. (This might be worth a post by itself, and is very Litany of Gendlin.)
More recently, the drug modafinil (brand name: Provigil) has become the brain-booster of choice for a growing number of Americans. According to the FDA, modafinil is intended to bolster “wakefulness” in people with narcolepsy, obstructive sleep apnea or shift work disorder. But when people without those conditions take it, it has been linked with improvements in alertness, energy, focus and decision-making. A 2017 study found evidence that modafinil may enhance some aspects of brain connectivity, which could explain these benefits.
With something like creatine, you’d know if it helps you pump out another rep at the gym on a sustainable basis. With nootropics, you can easily trick yourself into believing they help your mindset. The ideal is to do a trial on yourself. Take identical looking nootropic pills and placebo pills for a couple weeks each, then see what the difference is. With only a third party knowing the difference, of course.
As with other nootropics, the way it works is still partially a mystery, but most research points to it acting as a weak dopamine reuptake inhibitor. Put simply, it increases your dopamine levels the same way cocaine does, but in a much less extreme fashion. The enhanced reward system it creates in the brain, however, makes it what Patel considers to be the most potent cognitive enhancer available; and he notes that some people go from sloth to superman within an hour or two of taking it.
^ EFSA Panel on Dietetic Products, Nutrition and Allergies; European Food Safety Authority (EFSA), Parma, Italy (2011). "Scientific Opinion on the substantiation of health claims related to L-theanine from Camellia sinensis (L.) Kuntze (tea) and improvement of cognitive function (ID 1104, 1222, 1600, 1601, 1707, 1935, 2004, 2005), alleviation of psychological stress (ID 1598, 1601), maintenance of normal sleep (ID 1222, 1737, 2004) and reduction of menstrual discomfort (ID 1599) pursuant to Article 13(1) of Regulation (EC) No 1924/2006". EFSA Journal. 9 (6): 2238. doi:10.2903/j.efsa.2011.2238.