Nootropics (// noh-ə-TROP-iks)—also called smart drugs, memory enhancers, neuro enhancers, cognitive enhancers, and intelligence enhancers—are drugs, supplements, nutraceuticals, and functional foods that improve one or more aspects of mental function. Specific effects can include improvements to working memory, motivation, or attention. The word nootropic was coined in 1972 by a Romanian psychologist and chemist, Corneliu E. Giurgea, from the Greek words νους nous, or "mind", and τρέπειν trepein meaning to bend or turn.
Availability and prevalence
There are only a few drugs that are known to improve some aspect of cognition. Many more are in different stages of development. The most commonly used class of drug is stimulants, such as caffeine.
These drugs are purportedly used primarily to treat cognitive or motor function difficulties attributable to disorders such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and ADHD. Some researchers, however, report more widespread use despite concern for further research. Nevertheless, intense marketing may not correlate with efficacy. While scientific studies support the beneficial effects of some compounds, manufacturer's marketing claims for dietary supplements are usually not formally tested and verified by independent entities.
In academia, nootropics have been used to increase productivity, despite their long-term effects lacking conclusive research in healthy individuals. The use of prescription stimulants is especially prevalent among students attending academically competitive colleges. Surveys suggest that 0.7–4.5% of German students have used cognitive enhancers in their lifetime. Stimulants such as dimethylamylamine and methylphenidate are used on college campuses and by younger groups. Based upon studies of self-reported illicit stimulant use, 5–35% of college students use diverted ADHD stimulants, which are primarily used for performance enhancement rather than as recreational drugs.
Several factors positively and negatively influence the use of drugs to increase cognitive performance. Among them are personal characteristics, drug characteristics, and characteristics of the social context.
The main concern with pharmaceutical drugs is adverse effects, and these concerns apply to cognitive-enhancing drugs as well. Long-term safety data is typically unavailable for some types of nootropics (e.g., many non-pharmaceutical cognitive enhancers, newly developed pharmaceuticals and pharmaceuticals with short-term therapeutic use). Racetams—compounds that are structurally related to piracetam—have few serious adverse effects and low toxicity, but there is little evidence that they enhance cognition in individuals without cognitive impairments. While addiction to stimulants is sometimes identified as a cause for concern, a very large body of research on the therapeutic use of the "more addictive" psychostimulants indicate that addiction is fairly rare in therapeutic doses. On their safety profile, a systematic review from June 2015 asserted, "Evidence indicates that at low, clinically relevant doses, psychostimulants are devoid of the behavioral and neurochemical actions that define this class of drugs and instead act largely as cognitive enhancers."
In 2015, systematic medical reviews and meta-analyses of clinical research in humans established consensus that certain stimulants, only when used at low (therapeutic) concentrations, unambiguously enhance cognition in the general population; in particular, the classes of stimulants that demonstrate cognition-enhancing effects in humans act as direct agonists or indirect agonists of dopamine receptor D1, adrenoceptor A2, or both receptors in the prefrontal cortex. Relatively high doses of stimulants cause cognitive deficits.
- Amphetamine pharmaceuticals (Adderall, dextroamphetamine, and lisdexamfetamine [an inactive prodrug]) – systematic reviews and meta-analyses report that amphetamine benefits a range of aspects of cognitive control (e.g., attentional control, inhibitory control, episodic memory, and working memory, among others) in the general population, and these effects are especially notable in individuals with ADHD. A 2015 meta-analysis of high quality evidence found that therapeutic doses of amphetamine and methylphenidate improve performance on working memory, episodic memory, and inhibitory control tests in normal healthy adults. It also improves task saliency (motivation to perform a task) and performance on tedious tasks that require a high degree of effort.
- Methylphenidate – a substituted phenethylamine that improves cognitive control (e.g., working memory, episodic memory, and inhibitory control) in the general population. It also improves performance on tedious tasks that require a high degree of effort. At above optimal doses, methylphenidate has off target effects that can decrease learning by activating neurons not involved in the task at hand. It has the ability to inhibit processing of irrelevant tasks in the prefrontal cortex and basal ganglia, enhancing task saliency.
- Eugeroics (armodafinil and modafinil) – wakefulness promoting agents; modafinil increases alertness, particularly in sleep deprived individuals, and was noted to facilitate reasoning and problem solving in a systematic review. They are clinically prescribed for narcolepsy, shift work sleep disorder, and daytime sleepiness remaining after sleep apnea treatments.
- Xanthines (most notably, caffeine) – shown to increase alertness, performance, and, in some studies, memory. Children and adults who consume low doses of caffeine showed increased alertness, yet a higher dose was needed to improve performance. A 2014 systematic review and meta-analysis found that concurrent caffeine and L-theanine use has synergistic psychoactive effects that promote alertness, attention, and task switching; these effects are most pronounced during the first hour post-dose.
- Nicotine – A meta-analysis of 41 double-blind, placebo-controlled studies concluded that nicotine or smoking had significant positive effects on aspects of fine motor abilities, alerting and orienting attention, and episodic and working memory.
- Phosphatidylserine (a phospholipid) with DHA and EPA (omega-3 fatty acids) – two Cochrane Collaboration reviews on the use of supplemental omega-3 fatty acids alone (without phosphatidylserine) for ADHD and learning disorders conclude that there is limited evidence of treatment benefits for either disorder.
- Tianeptine – enhances several metrics of cognition in animal models. It has also been shown to prevent stress-induced dendritic remodeling in various brain structures, and antagonizes alcohol's neurodegenerative effects.
- L-theanine – see the Xanthines entry above.
- Valproate – a study has suggested that valproate may be able to enhance the cognitive ability of absolute pitch.
- Bacopa monnieri – A nutraceutical herb. Two review articles concluded that there is some evidence for memory-enhancing effects, but further research is needed.
- Panax ginseng – A review by the Cochrane Collaboration concluded that "there is a lack of convincing evidence to show a cognitive enhancing effect of Panax ginseng in healthy participants and no high quality evidence about its efficacy in patients with dementia." According to the National Center for Complementary and Integrative Health "Although Asian ginseng has been widely studied for a variety of uses, research results to date do not conclusively support health claims associated with the herb." According to a review published in the journal "Advances in Nutrition", multiple RCTs in healthy volunteers have indicated increases in accuracy of memory, speed in performing attention tasks and improvement in performing difficult mental arithmetic tasks, as well as reduction in fatigue and improvement in mood.
- Salvia officinalis – Although some evidence is suggestive of cognition benefits, the study quality is so poor that no conclusions can be drawn from it.
- Ginkgo biloba – Different reviews come to different conclusions. A 2009 Cochrane review found not enough evidence to make conclusions in those with dementia. Another review stated "there is consistent evidence that chronic administration improves selective attention, some executive processes and long-term memory for verbal and non-verbal material."
The racetams are structurally similar compounds, such as pramiracetam, oxiracetam, coluracetam, and aniracetam, which are often marketed as cognitive enhancers and sold over-the-counter. Racetams are often referred to as nootropics, but this property of the drug class is not well established. The racetams have poorly understood mechanisms of action; however, piracetam and aniracetam are known to act as positive allosteric modulators of AMPA receptors and appear to modulate cholinergic systems.
- Cognitive science
- Human enhancement
- Neurobiological effects of physical exercise#Cognitive control and memory
- "Dorlands Medical Dictionary". Archived from the original on January 30, 2008.
- Lanni C, Lenzken SC, Pascale A, et al. (March 2008). "Cognition enhancers between treating and doping the mind". Pharmacol. Res. 57 (3): 196–213. doi:10.1016/j.phrs.2008.02.004. PMID 18353672.
- Gazzaniga, Michael S. (2006). The Ethical Brain: The Science of Our Moral Dilemmas (P.S.). New York, N.Y: Harper Perennial. p. 184. ISBN 0-06-088473-8.
- Giurgea C (1972). "[Pharmacology of integrative activity of the brain. Attempt at nootropic concept in psychopharmacology] ("Vers une pharmacologie de l'active integrative du cerveau: Tentative du concept nootrope en psychopharmacologie")". Actual Pharmacol (Paris) (in French) 25: 115–56. PMID 4541214.
- "nootropicTranslation". Retrieved October 6, 2014.
- Sahakian B; Morein-Zamir S (December 2007). "Professor's little helper". Nature 450 (7173): 1157–9. Bibcode:2007Natur.450.1157S. doi:10.1038/4501157a. PMID 18097378.
- Greely, Henry; Sahakian, Barbara; Harris, John; Kessler, Ronald C.; Gazzaniga, Michael; Campbell, Philip; Farah, Martha J. (December 10, 2008). "Towards responsible use of cognitive-enhancing drugs by the healthy". Nature (Nature Publishing Group) 456 (7223): 702–705. Bibcode:2008Natur.456..702G. doi:10.1038/456702a. ISSN 1476-4687. OCLC 01586310. PMID 19060880. Retrieved March 25, 2014. (subscription required (. ))
- "Smart Drugs and Should We Take Them?". Dolan DNA Learning Center. Retrieved November 4, 2012.
- "Dietary Supplements: What You Need to Know". US Food and Drug Administration. Retrieved February 14, 2015.
- McCabe, Sean Esteban; Knight, John R.; Teter, Christian J.; Wechsler, Henry (January 1, 2005). "Non-medical use of prescription stimulants among US college students: prevalence and correlates from a national survey". Addiction 100 (1): 96–106. doi:10.1111/j.1360-0443.2005.00944.x. PMID 15598197. Retrieved August 15, 2013.
- Sattler, S.; Sauer, C.; Mehlkop, G.; Graeff, P. (2013). "The Rationale for Consuming Cognitive Enhancement Drugs in University Students and Teachers". PLoS ONE 8 (7): e68821. doi:10.1371/journal.pone.0068821.
- Sattler, Sebastian; Wiegel, Constantin (February 25, 2013). "Cognitive Test Anxiety and Cognitive Enhancement: The Influence of Students’ Worries on Their Use of Performance-Enhancing Drugs". Substance Use & Misuse (Informa Healthcare New York) 48 (3): 220–232. doi:10.3109/10826084.2012.751426. Retrieved April 5, 2014.
- Bossaer, John. "The Use and Misuse of Prescription Stimulants as "Cognitive Enhancers" by Students at One Academic Health Sciences Center". Academic Medicine. Retrieved October 6, 2014.
Overall, 11.3% of responders admitted to misusing prescription stimulants. There was more misuse by respiratory therapy students, although this was not statistically significant (10.9% medicine, 9.7% pharmacy, 26.3% respiratory therapy; P = .087). Reasons for prescription stimulant misuse included to enhance alertness/energy (65.9%), to improve academic performance (56.7%), to experiment (18.2%), and to use recreationally/get high (4.5%).
- Teter CJ, McCabe SE, LaGrange K, Cranford JA, Boyd CJ (October 2006). "Illicit use of specific prescription stimulants among college students: prevalence, motives, and routes of administration". Pharmacotherapy 26 (10): 1501–1510. doi:10.1592/phco.26.10.1501. PMC 1794223. PMID 16999660.
- Weyandt LL, Oster DR, Marraccini ME, Gudmundsdottir BG, Munro BA, Zavras BM, Kuhar B (September 2014). "Pharmacological interventions for adolescents and adults with ADHD: stimulant and nonstimulant medications and misuse of prescription stimulants". Psychol. Res. Behav. Manag. 7: 223–249. doi:10.2147/PRBM.S47013. PMC 4164338. PMID 25228824.
misuse of prescription stimulants has become a serious problem on college campuses across the US and has been recently documented in other countries as well. ... Indeed, large numbers of students claim to have engaged in the nonmedical use of prescription stimulants, which is reflected in lifetime prevalence rates of prescription stimulant misuse ranging from 5% to nearly 34% of students.
- Clemow DB, Walker DJ (September 2014). "The potential for misuse and abuse of medications in ADHD: a review". Postgrad. Med. 126 (5): 64–81. doi:10.3810/pgm.2014.09.2801. PMID 25295651.
Overall, the data suggest that ADHD medication misuse and diversion are common health care problems for stimulant medications, with the prevalence believed to be approximately 5% to 10% of high school students and 5% to 35% of college students, depending on the study.
- Sattler, Sebastian; Mehlkop, Guido; Graeff, Peter; Sauer, Carsten (February 1, 2014). "Evaluating the drivers of and obstacles to the willingness to use cognitive enhancement drugs: the influence of drug characteristics, social environment, and personal characteristics". Substance Abuse Treatment, Prevention, and Policy. BioMed Central Ltd. p. 8. doi:10.1186/1747-597X-9-8. ISSN 1747-597X. Retrieved April 5, 2014.
- Sattler, Sebastian; Forlini, Cynthia; Racine, Éric; Sauer, Carsten (August 5, 2013). "Impact of Contextual Factors and Substance Characteristics on Perspectives toward Cognitive Enhancement". PLOS ONE (PLOS) 8 (8): e71452. doi:10.1371/journal.pone.0071452. ISSN 1932-6203. LCCN 2006214532. OCLC 228234657. Retrieved April 5, 2014.
- Malykh AG, Sadaie MR (February 2010). "Piracetam and piracetam-like drugs: from basic science to novel clinical applications to CNS disorders". Drugs 70 (3): 287–312. doi:10.2165/11319230-000000000-00000. PMID 20166767.
- Gouliaev AH, Senning A (May 1994). "Piracetam and other structurally related nootropics". Brain Res. Brain Res. Rev. 19 (2): 180–222. doi:10.1016/0165-0173(94)90011-6. PMID 8061686.
- Noble KA (December 2012). "Brain gain: adolescent use of stimulants for achievement". J. Perianesth. Nurs. 27 (6): 415–9. doi:10.1016/j.jopan.2012.09.001. PMID 23164208.
- Stolerman IP (2010). Stolerman IP, ed. Encyclopedia of Psychopharmacology. Berlin; London: Springer. p. 78. ISBN 9783540686989.
- Millichap JG (2010). "Chapter 3: Medications for ADHD". In Millichap JG. Attention Deficit Hyperactivity Disorder Handbook: A Physician's Guide to ADHD (2nd ed.). New York: Springer. pp. 121–123. ISBN 9781441913968.
- Huang YS, Tsai MH (July 2011). "Long-term outcomes with medications for attention-deficit hyperactivity disorder: current status of knowledge". CNS Drugs 25 (7): 539–554. doi:10.2165/11589380-000000000-00000. PMID 21699268.
- Spencer RC, Devilbiss DM, Berridge CW (June 2015). "The Cognition-Enhancing Effects of Psychostimulants Involve Direct Action in the Prefrontal Cortex". Biol. Psychiatry 77 (11): 940–950. doi:10.1016/j.biopsych.2014.09.013. PMID 25499957.
The procognitive actions of psychostimulants are only associated with low doses. Surprisingly, despite nearly 80 years of clinical use, the neurobiology of the procognitive actions of psychostimulants has only recently been systematically investigated. Findings from this research unambiguously demonstrate that the cognition-enhancing effects of psychostimulants involve the preferential elevation of catecholamines in the PFC and the subsequent activation of norepinephrine α2 and dopamine D1 receptors. ... This differential modulation of PFC-dependent processes across dose appears to be associated with the differential involvement of noradrenergic α2 versus α1 receptors. Collectively, this evidence indicates that at low, clinically relevant doses, psychostimulants are devoid of the behavioral and neurochemical actions that define this class of drugs and instead act largely as cognitive enhancers (improving PFC-dependent function). This information has potentially important clinical implications as well as relevance for public health policy regarding the widespread clinical use of psychostimulants and for the development of novel pharmacologic treatments for attention-deficit/hyperactivity disorder and other conditions associated with PFC dysregulation. ... In particular, in both animals and humans, lower doses maximally improve performance in tests of working memory and response inhibition, whereas maximal suppression of overt behavior and facilitation of attentional processes occurs at higher doses.
- Goldman P (2001). "Herbal medicines today and the roots of modern pharmacology". Annals of Internal Medicine 135 (8 Pt 1): 594–600. doi:10.7326/0003-4819-135-8_Part_1-200110160-00010. PMID 11601931.
- Ilieva IP, Hook CJ, Farah MJ (January 2015). "Prescription Stimulants' Effects on Healthy Inhibitory Control, Working Memory, and Episodic Memory: A Meta-analysis". J. Cogn. Neurosci.: 1–21. doi:10.1162/jocn_a_00776. PMID 25591060.
The present meta-analysis was conducted to estimate the magnitude of the effects of methylphenidate and amphetamine on cognitive functions central to academic and occupational functioning, including inhibitory control, working memory, short-term episodic memory, and delayed episodic memory. In addition, we examined the evidence for publication bias. Forty-eight studies (total of 1,409 participants) were included in the analyses. We found evidence for small but significant stimulant enhancement effects on inhibitory control and short-term episodic memory. Small effects on working memory reached significance, based on one of our two analytical approaches. Effects on delayed episodic memory were medium in size. However, because the effects on long-term and working memory were qualified by evidence for publication bias, we conclude that the effect of amphetamine and methylphenidate on the examined facets of healthy cognition is probably modest overall. In some situations, a small advantage may be valuable, although it is also possible that healthy users resort to stimulants to enhance their energy and motivation more than their cognition. ... Earlier research has failed to distinguish whether stimulants’ effects are small or whether they are nonexistent (Ilieva et al., 2013; Smith & Farah, 2011). The present findings supported generally small effects of amphetamine and methylphenidate on executive function and memory. Specifically, in a set of experiments limited to high-quality designs, we found significant enhancement of several cognitive abilities. ...
The results of this meta-analysis cannot address the important issues of individual differences in stimulant effects or the role of motivational enhancement in helping perform academic or occupational tasks. However, they do confirm the reality of cognitive enhancing effects for normal healthy adults in general, while also indicating that these effects are modest in size.
- Bagot KS, Kaminer Y (April 2014). "Efficacy of stimulants for cognitive enhancement in non-attention deficit hyperactivity disorder youth: a systematic review". Addiction 109 (4): 547–557. doi:10.1111/add.12460. PMID 24749160.
- Wood S, Sage JR, Shuman T, Anagnostaras SG (January 2014). "Psychostimulants and cognition: a continuum of behavioral and cognitive activation". Pharmacol. Rev. 66 (1): 193–221. doi:10.1124/pr.112.007054. PMID 24344115.
- Malenka RC, Nestler EJ, Hyman SE (2009). "Chapter 13: Higher Cognitive Function and Behavioral Control". In Sydor A, Brown RY. Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd ed.). New York: McGraw-Hill Medical. p. 318. ISBN 9780071481274.
Mild dopaminergic stimulation of the prefrontal cortex enhances working memory. ...
Therapeutic (relatively low) doses of psychostimulants, such as methylphenidate and amphetamine, improve performance on working memory tasks both in in normal subjects and those with ADHD. Positron emission tomography (PET) demonstrates that methylphenidate decreases regional cerebral blood flow in the doroslateral prefrontal cortex and posterior parietal cortex while improving performance of a spacial working memory task. This suggests that cortical networks that normally process spatial working memory become more efficient in response to the drug. ... [It] is now believed that dopamine and norepinephrine, but not serotonin, produce the beneficial effects of stimulants on working memory. At abused (relatively high) doses, stimulants can interfere with working memory and cognitive control ... stimulants act not only on working memory function, but also on general levels of arousal and, within the nucleus accumbens, improve the saliency of tasks. Thus, stimulants improve performance on effortful but tedious tasks ... through indirect stimulation of dopamine and norepinephrine receptors.
- Linssen AM, Sambeth A, Vuurman EF, Riedel WJ (June 2014). "Cognitive effects of methylphenidate in healthy volunteers: a review of single dose studies". Int. J. Neuropsychopharmacol. 17 (6): 961–977. doi:10.1017/S1461145713001594. PMID 24423151.
The studies reviewed here show that single doses of MPH improve cognitive performance in the healthy population in the domains of working memory (65% of included studies) and speed of processing (48%), and to a lesser extent may also improve verbal learning and memory (31%), attention and vigilance (29%) and reasoning and problem solving (18%), but does not have an effect on visual learning and memory. MPH effects are dose-dependent and the dose-response relationship differs between cognitive domains.
- Urban, KR; Gao, WJ (2014). "Performance enhancement at the cost of potential brain plasticity: neural ramifications of nootropic drugs in the healthy developing brain.". Frontiers in Systems Neuroscience 8: 38. doi:10.3389/fnsys.2014.00038. PMID 24860437.
- Huurne, Niels ter; Fallon, Sean James; Schouwenburg, Martine van; Schaaf, Marieke van der; Buitelaar, Jan; Jensen, Ole; Cools, Roshan (2015-09-09). "Methylphenidate alters selective attention by amplifying salience". Psychopharmacology 232 (23): 4317–4323. doi:10.1007/s00213-015-4059-y. ISSN 0033-3158.
- Mereu M, Bonci A, Newman AH, Tanda G (October 2013). "The neurobiology of modafinil as an enhancer of cognitive performance and a potential treatment for substance use disorders". Psychopharmacology (Berl.) 229 (3): 415–34. doi:10.1007/s00213-013-3232-4. PMID 23934211.
- "Modafinil". MedlinePlus. Retrieved August 19, 2014.
- Rogers, P. (2007). "Caffeine, mood and mental performance in everyday life". Psychology Today 32 (1): 84–89. doi:10.1111/j.1467-3010.2007.00607.x.
- Kiefer, I. (2007). "Brain Food". Scientific American Mind 18 (5): 58–63. doi:10.1038/scientificamericanmind1007-58. Retrieved November 1, 2009.
- Camfield DA, Stough C, Farrimond J, Scholey AB (2014). "Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis". Nutr. Rev. 72 (8): 507–22. doi:10.1111/nure.12120. PMID 24946991.
- Heishman SJ, Kleykamp BA, Singleton EG (June 2010). "Meta-analysis of the acute effects of nicotine and smoking on human performance". Psychopharmacology (Berl). 210 (4): 453–69. doi:10.1007/s00213-010-1848-1. PMC 3151730. PMID 20414766. Retrieved March 23, 2012.
- Gillies D, Sinn JKh, Lad SS, Leach MJ, Ross MJ (2012). "Polyunsaturated fatty acids (PUFA) for attention deficit hyperactivity disorder (ADHD) in children and adolescents". Cochrane Database Syst Rev 7: CD007986. doi:10.1002/14651858.CD007986.pub2. PMID 22786509.
- Tan ML, Ho JJ, Teh KH (2012). "Polyunsaturated fatty acids (PUFAs) for children with specific learning disorders". Cochrane Database Syst Rev 12: CD009398. doi:10.1002/14651858.CD009398.pub2. PMID 23235675.
- McEwen BS, Chattarji S, Diamond DM, Jay TM, Reagan LP, Svenningsson P, Fuchs E (March 2010). "The neurobiological properties of tianeptine (Stablon): from monoamine hypothesis to glutamatergic modulation". Mol. Psychiatry 15 (3): 237–49. doi:10.1038/mp.2009.80. PMC 2902200. PMID 19704408.
Cognitive deficits, such as an impairment of attention, memory and problem solving, have often been reported in patients with depressive disorders (69). Cognitive deficits and memory impairments in patients with depression may arise via disruption of the hypothalamic-pituitary adrenal (HPA) axis through hippocampal volume loss and changes in the amygdala. The magnitude of the hippocampal shrinkage reported in certain experimental conditions may partly underlie some of cognitive deficits that accompany major depression. Conversely, any prevention or restoration of these morphological changes in the hippocampus should be parallel to procognitive/promnesiant effects. Accordingly, tianeptine has particularly favorable effects on cognitive functions and the positive effect of tianeptine may be mediated through its upregulation of neurogenesis, but of course, the impact of neurogenesis on cognitive functions remains a matter of controversial debate.
Tianeptine prevents and reverses stress-induced glucocorticoid-mediated dendritic remodeling in CA3 pyramidal neurons in the hippocampus (40,41) and stress-induced increases in dendritic length and branching in the amygdala (50). Tianeptine blocks the dendritic remodeling caused by stress or glucocorticoids (41), blocks stress-induced impairments of spatial memory performance in radial and Y-maze (70,71) and antagonizes the deleterious effects of alcohol (72).
In a validated model of hippocampal-dependent memory impairment and synaptic plasticity changes by predator stress, acute tianeptine can prevent the deleterious effects of stress on spatial memory, an effect that does not depend on corticosterone levels (73). Tianeptine also facilitates focused attention behavior in the cat in response to its environment or towards a significant stimulus (74). It was shown to exert improving effects on learning as well as on working memory and on reference memory in rodents (72) and to exhibit vigilance-enhancing effects in rats (75) and monkeys (76)...
- Gervain Judit, Vines Bradley W., Chen Lawrence M., Seo Rubo J, Hensch Takao K., Werker Janet F, Young Allan H (2013). "Valproate reopens critical-period learning of absolute pitch". Frontiers in Systems Neuroscience 7 (00102). doi:10.3389/fnsys.2013.00102. PMC 3848041. PMID 24348349.
- Aguiar S, Borowski T (August 2013). "Neuropharmacological review of the nootropic herb Bacopa monnieri". Rejuvenation Res 16 (4): 313–26. doi:10.1089/rej.2013.1431. PMC 3746283. PMID 23772955.
- Pase MP, Kean J, Sarris J, Neale C, Scholey AB, Stough C (July 2012). "The cognitive-enhancing effects of Bacopa monnieri: a systematic review of randomized, controlled human clinical trials". J Altern Complement Med 18 (7): 647–52. doi:10.1089/acm.2011.0367. PMID 22747190.
- Geng J, Dong J, Ni H, Lee MS, Wu T, Jiang K, Wang G, Zhou AL, Malouf R (2010). "Ginseng for cognition". Cochrane Database Syst Rev (12): CD007769. doi:10.1002/14651858.CD007769.pub2. PMID 21154383.
- "Asian Ginseng | NCCIH".
- Kennedy DO, Wightman EL (January 2011). "Herbal extracts and phytochemicals: plant secondary metabolites and the enhancement of human brain function". Adv Nutr. 2 (1): 32–50. doi:10.3945/an.110.000117. PMC 3042794. PMID 22211188.
- Miroddi M, Navarra M, Quattropani MC, Calapai F, Gangemi S, Calapai G (2014). "Systematic review of clinical trials assessing pharmacological properties of Salvia species on memory, cognitive impairment and Alzheimer's disease". CNS Neurosci Ther (Systematic review) 20 (6): 485–95. doi:10.1111/cns.12270. PMID 24836739.
Unfortunately, promising beneficial effects showed in clinical studies are debased by methodological issues
- Birks, J; Grimley Evans, J (January 21, 2009). "Ginkgo biloba for cognitive impairment and dementia.". The Cochrane database of systematic reviews (1): CD003120. doi:10.1002/14651858.CD003120.pub3. PMID 19160216.
- Kaschel R (2009). "Ginkgo biloba: specificity of neuropsychological improvement—a selective review in search of differential effects". Hum Psychopharmacol 24 (5): 345–70. doi:10.1002/hup.1037. PMID 19551805.
- Malenka RC, Nestler EJ, Hyman SE (2009). Sydor A, Brown RY, ed. Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd ed.). New York: McGraw-Hill Medical. p. 454. ISBN 9780071481274.
- Gualtieri F, Manetti D, Romanelli MN, Ghelardini C (2002). "Design and study of piracetam-like nootropics, controversial members of the problematic class of cognition-enhancing drugs". Curr. Pharm. Des. 8 (2): 125–38. doi:10.2174/1381612023396582. PMID 11812254.
- Whose well-being? Common conceptions and misconceptions in the enhancement debate – doi:10.3389/fnsys.2014.00148 PMID 25191232 (Frontiers in Systems Neuroscience, August 2014)