Caffeine (Examine.com; FDA adverse events) is of course the most famous stimulant around. But consuming 200mg or more a day, I have discovered the downside: it is addictive and has a nasty withdrawal - headaches, decreased motivation, apathy, and general unhappiness. (It’s a little amusing to read academic descriptions of caffeine addiction9; if caffeine were a new drug, I wonder what Schedule it would be in and if people might be even more leery of it than modafinil.) Further, in some ways, aside from the ubiquitous placebo effect, caffeine combines a mix of weak performance benefits (Lorist & Snel 2008, Nehlig 2010) with some possible decrements, anecdotally and scientifically:

…Phenethylamine is intrinsically a stimulant, although it doesn’t last long enough to express this property. In other words, it is rapidly and completely destroyed in the human body. It is only when a number of substituent groups are placed here or there on the molecule that this metabolic fate is avoided and pharmacological activity becomes apparent.
The compound has great nootropic properties that includes memory enhancement and protection against brain aging. There are studies that suggest that the compound is an effective treatment for disorders like vascular dementia, Alzheimer’s, brain stroke, anxiety and depression. However, there are some side effects associated with Alpha GPC, like headache, heartburn, dizziness, skin rashes, insomnia, and confusion.
Legal Disclaimer Do Not exceed recommended dose for Colon Clean. Pregnant or nursing mothers, children under 18, and individuals with a known medical condition should consult a physician before using this or any dietary supplement. Be careful when using supplements with other supplements or prescription pharmaceuticals. This product is not intended to diagnose, treat, cure, or prevent any disease.
Omega-3 fatty acids: DHA and EPA – two Cochrane Collaboration reviews on the use of supplemental omega-3 fatty acids for ADHD and learning disorders conclude that there is limited evidence of treatment benefits for either disorder.[42][43] Two other systematic reviews noted no cognition-enhancing effects in the general population or middle-aged and older adults.[44][45]
I almost resigned myself to buying patches to cut (and let the nicotine evaporate) and hope they would still stick on well enough afterwards to be indistinguishable from a fresh patch, when late one sleepless night I realized that a piece of nicotine gum hanging around on my desktop for a week proved useless when I tried it, and that was the answer: if nicotine evaporates from patches, then it must evaporate from gum as well, and if gum does evaporate, then to make a perfect placebo all I had to do was cut some gum into proper sizes and let the pieces sit out for a while. (A while later, I lost a piece of gum overnight and consumed the full 4mg to no subjective effect.) Google searches led to nothing indicating I might be fooling myself, and suggested that evaporation started within minutes in patches and a patch was useless within a day. Just a day is pushing it (who knows how much is left in a useless patch?), so I decided to build in a very large safety factor and let the gum sit for around a month rather than a single day.
It wasn't always helpful, but it does work sometimes. The first two days gave me stomach and head pain, so I began to test with taking before or after food, and with or without food. The bottle says to take before food, but I preferred taking this with food, more food is better. This doesn't go well in the stomach with something like chocolate, so take this with something like bread or a meal. More importantly, stay very hydrated unless you want a headache, these pills are very hydro-demanding. The pills also work better if you get your blood moving, just a short walk is fine. Energy drinks and coffee go very well with these, as I had a very clear minded experience when taking these with a Monster Java, it was like a cool breeze blowing away the mental fog.
Harriet Hall, MD also known as The SkepDoc, is a retired family physician who writes about pseudoscience and questionable medical practices. She received her BA and MD from the University of Washington, did her internship in the Air Force (the second female ever to do so),  and was the first female graduate of the Air Force family practice residency at Eglin Air Force Base. During a long career as an Air Force physician, she held various positions from flight surgeon to DBMS (Director of Base Medical Services) and did everything from delivering babies to taking the controls of a B-52. She retired with the rank of Colonel.  In 2008 she published her memoirs, Women Aren't Supposed to Fly.
Nicotine’s stimulant effects are general and do not come with the same tweakiness and aggression associated with the amphetamines, and subjectively are much cleaner with less of a crash. I would say that its stimulant effects are fairly strong, around that of modafinil. Another advantage is that nicotine operates through nicotinic receptors and so doesn’t cross-tolerate with dopaminergic stimulants (hence one could hypothetically cycle through nicotine, modafinil, amphetamines, and caffeine, hitting different receptors each time).
The nootropics I’m taking are called RISE, and they're made by a company called Nootrobox, which was started by Geoffrey Woo, a young Stanford computer science graduate. There's no one common ingredient in nootropics; what unites them is the intent to improve brain performance. The RISE stack, which costs $29 plus shipping for 30 pills, contains 350 mg of bacopa monnieri powder (an herb that is commonly used medicinally in South Asia), 100 mg of L-theanine (an amino acid found in green tea), and 50 mg of caffeine (about the amount in a can of Diet Coke). Like most nootropics, the RISE stack itself isn't FDA-approved for use as a cognitive enhancer, but Nootrobox says that the compounds within it are approved as dietary supplements. "We use the precise ingredients at the right dosages and the right ratios as supported by double-blind, peer-reviewed clinicals," Nootrobox's site claims.

The evidence? Although everyone can benefit from dietary sources of essential fatty acids, supplementation is especially recommended for people with heart disease. A small study published in 2013 found that DHA may enhance memory and reaction time in healthy young adults. However, a more recent review suggested that there is not enough evidence of any effect from omega 3 supplementation in the general population.
Exercise is also important, says Lebowitz. Studies have shown it sharpens focus, elevates your mood and improves concentration. Likewise, maintaining a healthy social life and getting enough sleep are vital, too. Studies have consistently shown that regularly skipping out on the recommended eight hours can drastically impair critical thinking skills and attention.
Before taking any supplement or chemical, people want to know if there will be long term effects or consequences, When Dr. Corneliu Giurgea first authored the term “nootropics” in 1972, he also outlined the characteristics that define nootropics. Besides the ability to benefit memory and support the cognitive processes, Dr. Giurgea believed that nootropics should be safe and non-toxic.
The use of cognition-enhancing drugs by healthy individuals in the absence of a medical indication spans numerous controversial issues, including the ethics and fairness of their use, concerns over adverse effects, and the diversion of prescription drugs for nonmedical uses, among others.[1][2] Nonetheless, the international sales of cognition-enhancing supplements exceeded US$1 billion in 2015 when global demand for these compounds grew.[3]
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