To thwart the rise of non-prescription nootropics, opponents may rally for increased regulation; however, at present, there is insufficient research available to support that non-prescription nootropics pose a danger to public health. Prescription nootropics, such as Ritalin, are already regulated. Further, these drugs have a proven beneficial treatment purpose for intended users.
[…] 2. Blueberries: Also called “brainberries” by Dr. Steven Platt, MD author of Superfoods Rx: Fourteen Foods Proven to Change Your Life, blueberries have one of the highest antioxidant capacities of all fruits and vegetables and are known to improve memory and cognitive function. They have memory-protecting properties and have even been associated with the prevention of Alzheimer’s disease. Add some blueberries to your breakfast and you may not need to check that to-do list several times throughout the day. Also Read The 7 Best Brain Boosting Supplements […]
1. Stough, C., Lloyd, J., Clarke, J., Downey, L. A., Hutchison, C. W., Rodgers, T., & Nathan, P. J. (2001). The chronic effects of an extract of Bacopa monniera (Brahmi) on cognitive function in healthy human subjects. Psychopharmacology (Berl), 156(4), 481-484. 2. Ishaque, S., Shamseer, L., Bukutu, C., & Vohra, S. (2012). Rhodiola rosea for physical and mental fatigue: a systematic review. BMC Complementary and Alternative Medicine, 12(1), 70. doi:10.1186/1472-6882-12-703. Pase, M. P., Kean, J., Sarris, J., Neale, C., Scholey, A. B., & Stough, C. (2012). The cognitive-enhancing effects of Bacopa monnieri: a systematic review of randomized, controlled human clinical trials. J Altern Complement Med, 18(7), 647-652. doi:10.1089/acm.2011.03674. Raghav, S., Singh, H., Dalal, P. K., Srivastava, J. S., & Asthana, O. P. (2006). Randomized controlled trial of standardized Bacopa monniera extract in age-associated memory impairment. Indian J Psychiatry, 48(4), 238-242. doi:10.4103/0019-5545.315555. Neale, C., Camfield, D., Reay, J., Stough, C., & Scholey, A. (2013). Cognitive effects of two nutraceuticals Ginseng and Bacopa [...]: a review and comparison of effect sizes. British Journal of Clinical Pharmacology, 75(3), 728-737. doi:10.1111/bcp.120026. Prynne, C. J., Thane, C. W., Prentice, A., & Wadsworth, M. E. (2005). Intake and sources of phylloquinone (vitamin K(1)) in 4-year-old British children: comparison between 1950 and the 1990s. Public Health Nutr, 8(2), 171-180.7. Ferland, G. (2012). Vitamin K and the nervous system: an overview of its actions. Adv Nutr, 3(2), 204-212. doi:10.3945/an.111.0017848. Zeidan, Y. H., & Hannun, Y. A. (2007). Translational aspects of sphingolipid metabolism. Trends in molecular medicine, 13(8), 327-336.9. Beulens, J. W., Bots, M. L., Atsma, F., Bartelink, M. L., Prokop, M., Geleijnse, J. M., . . . van der Schouw, Y. T. (2009). High dietary menaquinone intake is associated with reduced coronary calcification. Atherosclerosis, 203(2), 489-493. doi:10.1016/j.atherosclerosis.2008.07.01010. Geleijnse, J. M., Vermeer, C., Grobbee, D. E., Schurgers, L. J., Knapen, M. H., van der Meer, I. M., . . . Witteman, J. C. (2004). Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr, 134(11), 3100-3105.11. Theuwissen, E., Magdeleyns, E. J., Braam, L. A., Teunissen, K. J., Knapen, M. H., Binnekamp, I. A., . . . Vermeer, C. (2014). Vitamin K status in healthy volunteers. Food Funct, 5(2), 229-234. doi:10.1039/c3fo60464k12. Barros, M. P., Poppe, S. C., & Bondan, E. F. (2014). Neuroprotective properties of the marine carotenoid astaxanthin and omega-3 fatty acids, and perspectives for the natural combination of both in krill oil. Nutrients, 6(3), 1293-1317.13. Pashkow, F. J., Watumull, D. G., & Campbell, C. L. (2008). Astaxanthin: a novel potential treatment for oxidative stress and inflammation in cardiovascular disease. Am J Cardiol, 101(10a), 58d-68d. doi:10.1016/j.amjcard.2008.02.01014. Annweiler, C., Schott, A. M., Berrut, G., Chauvire, V., Le Gall, D., Inzitari, M., & Beauchet, O. (2010). Vitamin D and ageing: neurological issues. Neuropsychobiology, 62(3), 139-150. doi:10.1159/00031857015. Brown, J., Bianco, J. I., McGrath, J. J., & Eyles, D. W. (2003). 1,25-dihydroxyvitamin D3 induces nerve growth factor, promotes neurite outgrowth and inhibits mitosis in embryonic rat hippocampal neurons. Neurosci Lett, 343(2), 139-143.16. Naveilhan, P., Neveu, I., Wion, D., & Brachet, P. (1996). 1,25-Dihydroxyvitamin D3, an inducer of glial cell line-derived neurotrophic factor. Neuroreport, 7(13), 2171-2175.17. Tangpricha, V., Pearce, E. N., Chen, T. C., & Holick, M. F. (2002). Vitamin D insufficiency among free-living healthy young adults. Am J Med, 112(8), 659-662.18. Annweiler, C., Allali, G., Allain, P., Bridenbaugh, S., Schott, A. M., Kressig, R. W., & Beauchet, O. (2009). Vitamin D and cognitive performance in adults: a systematic review. European Journal of Neurology, 16(10), 1083-1089. doi:10.1111/j.1468-1331.2009.02755.x19. Annweiler, C., Montero-Odasso, M., Llewellyn, D. J., Richard-Devantoy, S., Duque, G., & Beauchet, O. (2013). Meta-analysis of memory and executive dysfunctions in relation to vitamin D. J Alzheimers Dis, 37(1), 147-171. doi:10.3233/jad-13045220. Balion, C., Griffith, L. E., Strifler, L., Henderson, M., Patterson, C., Heckman, G., . . . Raina, P. (2012). Vitamin D, cognition, and dementia A systematic review and meta-analysis. Neurology, 79(13), 1397-1405.21. Dean, A. J., Bellgrove, M. A., Hall, T., Phan, W. M. J., Eyles, D. W., Kvaskoff, D., & McGrath, J. J. (2011). Effects of Vitamin D Supplementation on Cognitive and Emotional Functioning in Young Adults – A Randomised Controlled Trial. PLoS One, 6(11), e25966. doi:10.1371/journal.pone.002596622. Etgen, T., Sander, D., Bickel, H., Sander, K., & Forstl, H. (2012). Vitamin D deficiency, cognitive impairment and dementia: a systematic review and meta-analysis. Dement Geriatr Cogn Disord, 33(5), 297-305. doi:10.1159/00033970223. Fontani, G., Corradeschi, F., Felici, A., Alfatti, F., Migliorini, S., & Lodi, L. (2005). Cognitive and physiological effects of Omega-3 polyunsaturated fatty acid supplementation in healthy subjects. Eur J Clin Invest, 35(11), 691-699. doi:10.1111/j.1365-2362.2005.01570.x24. Huhn, S., Masouleh, S. K., Stumvoll, M., Villringer, A., & Witte, A. V. (2015). Components of a Mediterranean diet and their impact on cognitive functions in aging. Frontiers in aging neuroscience, 7.25. Bradbury, J. (2011). Docosahexaenoic Acid (DHA): An Ancient Nutrient for the Modern Human Brain. Nutrients, 3(5), 529-554. doi:10.3390/nu305052926. Einother, S. J., & Giesbrecht, T. (2013). Caffeine as an attention enhancer: reviewing existing assumptions. Psychopharmacology (Berl), 225(2), 251-274. doi:10.1007/s00213-012-2917-427. Johnson, L. C., Spinweber, C. L., & Gomez, S. A. (1990). Benzodiazepines and caffeine: effect on daytime sleepiness, performance, and mood. Psychopharmacology (Berl), 101(2), 160-167. 28. Smith, A., Kendrick, A., Maben, A., & Salmon, J. (1994). Effects of breakfast and caffeine on cognitive performance, mood and cardiovascular functioning. Appetite, 22(1), 39-55. doi:10.1006/appe.1994.100429. Smith, A. P., Kendrick, A. M., & Maben, A. L. (1992). Effects of breakfast and caffeine on performance and mood in the late morning and after lunch. Neuropsychobiology, 26(4), 198-204. doi:11892030. Smith, B. D., Davidson, R. A., & Green, R. L. (1993). Effects of caffeine and gender on physiology and performance: further tests of a biobehavioral model. Physiol Behav, 54(3), 415-422. 31. Warburton, D. M. (1995). Effects of caffeine on cognition and mood without caffeine abstinence. Psychopharmacology (Berl), 119(1), 66-70. 32. Wilhelmus, M. M., Hay, J. L., Zuiker, R. G., Okkerse, P., Perdrieu, C., Sauser, J., . . . Silber, B. Y. (2017). Effects of a single, oral 60 mg caffeine dose on attention in healthy adult subjects. J Psychopharmacol, 31(2), 222-232. doi:10.1177/026988111666859333. Fredholm, B. B., Battig, K., Holmen, J., Nehlig, A., & Zvartau, E. E. (1999). Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. Pharmacol Rev, 51(1), 83-133. 34. Borzelleca, J. F., Peters, D., & Hall, W. (2006). A 13-week dietary toxicity and toxicokinetic study with l-theanine in rats. Food Chem Toxicol, 44(7), 1158-1166. doi:10.1016/j.fct.2006.03.01435. Kimura, K., Ozeki, M., Juneja, L. R., & Ohira, H. (2007). L-Theanine reduces psychological and physiological stress responses. Biol Psychol, 74(1), 39-45. doi:10.1016/j.biopsycho.2006.06.00636. Tian, X., Sun, L., Gou, L., Ling, X., Feng, Y., Wang, L., . . . Liu, Y. (2013). Protective effect of l-theanine on chronic restraint stress-induced cognitive impairments in mice. Brain Res, 1503, 24-32. doi:10.1016/j.brainres.2013.01.04837. Unno, K., Fujitani, K., Takamori, N., Takabayashi, F., Maeda, K., Miyazaki, H., . . . Hoshino, M. (2011). Theanine intake improves the shortened lifespan, cognitive dysfunction and behavioural depression that are induced by chronic psychosocial stress in mice. Free Radic Res, 45(8), 966-974. doi:10.3109/10715762.2011.56686938. Unno, K., Tanida, N., Ishii, N., Yamamoto, H., Iguchi, K., Hoshino, M., . . . Yamada, H. (2013). Anti-stress effect of theanine on students during pharmacy practice: positive correlation among salivary alpha-amylase activity, trait anxiety and subjective stress. Pharmacol Biochem Behav, 111, 128-135. doi:10.1016/j.pbb.2013.09.00439. Dodd, F. L., Kennedy, D. O., Riby, L. M., & Haskell-Ramsay, C. F. (2015a). A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood. Psychopharmacology (Berl), 232(14), 2563-2576. doi:10.1007/s00213-015-3895-040. Rogers, P. J., Smith, J. E., Heatherley, S. V., & Pleydell-Pearce, C. W. (2008). Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. Psychopharmacology (Berl), 195(4), 569-577. doi:10.1007/s00213-007-0938-141. Foxe, J. J., Morie, K. P., Laud, P. J., Rowson, M. J., de Bruin, E. A., & Kelly, S. P. (2012). Assessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention task. Neuropharmacology, 62(7), 2320-2327. doi:10.1016/j.neuropharm.2012.01.02042. Giesbrecht, T., Rycroft, J. A., Rowson, M. J., & De Bruin, E. A. (2010). The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci, 13(6), 283-290. doi:10.1179/147683010x1261146076484043. Haskell, C. F., Kennedy, D. O., Milne, A. L., Wesnes, K. A., & Scholey, A. B. (2008). The effects of L-theanine, caffeine and their combination on cognition and mood. Biol Psychol, 77(2), 113-122. doi:10.1016/j.biopsycho.2007.09.00844. Kahathuduwa, C. N., Dassanayake, T. L., Amarakoon, A. M., & Weerasinghe, V. S. (2016). Acute effects of theanine, caffeine and theanine-caffeine combination on attention. Nutr Neurosci. doi:10.1080/1028415x.2016.114484545. Owen, G. N., Parnell, H., De Bruin, E. A., & Rycroft, J. A. (2008). The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci, 11(4), 193-198. doi:10.1179/147683008x30151346. Einother, S. J., Martens, V. E., Rycroft, J. A., & De Bruin, E. A. (2010). L-theanine and caffeine improve task switching but not intersensory attention or subjective alertness. Appetite, 54(2), 406-409. doi:10.1016/j.appet.2010.01.00347. Deijen, J. B., van der Beek, E. J., Orlebeke, J. F., & van den Berg, H. (1992). Vitamin B-6 supplementation in elderly men: effects on mood, memory, performance and mental effort. Psychopharmacology (Berl), 109(4), 489-496.48. Lewerin, C., Matousek, M., Steen, G., Johansson, B., Steen, B., & Nilsson-Ehle, H. (2005). Significant correlations of plasma homocysteine and serum methylmalonic acid with movement and cognitive performance in elderly subjects but no improvement from short-term vitamin therapy: a placebo-controlled randomized study. Am J Clin Nutr, 81(5), 1155-1162. 49. Bryan, J., Calvaresi, E., & Hughes, D. (2002). Short-term folate, vitamin B-12 or vitamin B-6 supplementation slightly affects memory performance but not mood in women of various ages. J Nutr, 132(6), 1345-1356. 50. Schneider, Z., & Stroinski, A. (1987). Comprehensive B12: chemistry, biochemistry, nutrition, ecology, medicine: Walter de Gruyter.51. Polich, J., & Gloria, R. (2001). Cognitive effects of a Ginkgo biloba/vinpocetine compound in normal adults: systematic assessment of perception, attention and memory. Hum Psychopharmacol, 16(5), 409-416. doi:10.1002/hup.30852. Subhan, Z., & Hindmarch, I. (1985). Psychopharmacological effects of vinpocetine in normal healthy volunteers. Eur J Clin Pharmacol, 28(5), 567-571. 53. Dollins, A. B., Krock, L. P., Storm, W. F., Wurtman, R. J., & Lieberman, H. R. (1995). L-tyrosine ameliorates some effects of lower body negative pressure stress. Physiol Behav, 57(2), 223-230. 54. Shurtleff, D., Thomas, J. R., Schrot, J., Kowalski, K., & Harford, R. (1994). Tyrosine reverses a cold-induced working memory deficit in humans. Pharmacol Biochem Behav, 47(4), 935-941. 55. Brzezinski, A., Vangel, M. G., Wurtman, R. J., Norrie, G., Zhdanova, I., Ben-Shushan, A., & Ford, I. (2005). Effects of exogenous melatonin on sleep: a meta-analysis. Sleep Med Rev, 9(1), 41-50. 56. Ferracioli-Oda, E., Qawasmi, A., & Bloch, M. H. (2013). Meta-Analysis: Melatonin for the Treatment of Primary Sleep Disorders. PLoS One, 8(5), e63773. doi:10.1371/journal.pone.006377357. Inagawa, K., Hiraoka, T., Kohda, T., Yamadera, W., & Takahashi, M. (2006). Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep and Biological Rhythms, 4(1), 75-77. doi:10.1111/j.1479-8425.2006.00193.x58. Bannai, M., Kawai, N., Ono, K., Nakahara, K., & Murakami, N. (2012). The Effects of Glycine on Subjective Daytime Performance in Partially Sleep-Restricted Healthy Volunteers. Front Neurol, 3, 61. doi:10.3389/fneur.2012.0006159. Yamadera, W., Inagawa, K., Chiba, S., Bannai, M., Takahashi, M., & Nakayama, K. (2007). Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep and Biological Rhythms, 5(2), 126-131. doi:10.1111/j.1479-8425.2007.00262.x60. Tuli, H. S., Kashyap, D., Sharma, A. K., & Sandhu, S. S. (2015). Molecular aspects of melatonin (MLT)-mediated therapeutic effects. Life Sci, 135, 147-157. doi:10.1016/j.lfs.2015.06.00461. Herxheimer, A., & Petrie, K. J. (2002). Melatonin for the prevention and treatment of jet lag. Cochrane Database Syst Rev(2), Cd001520. doi:10.1002/14651858.cd00152062. Deng, X., Song, Y., Manson, J. E., Signorello, L. B., Zhang, S. M., Shrubsole, M. J., . . . Dai, Q. (2013). Magnesium, vitamin D status and mortality: results from US National Health and Nutrition Examination Survey (NHANES) 2001 to 2006 and NHANES III. BMC Med, 11(1), 187. doi:10.1186/1741-7015-11-18763. Murck, H., & Steiger, A. (1998). Mg2+ reduces ACTH secretion and enhances spindle power without changing delta power during sleep in men -- possible therapeutic implications. Psychopharmacology (Berl), 137(3), 247-252. 64. Nielsen, F. H., Johnson, L. K., & Zeng, H. (2010). Magnesium supplementation improves indicators of low magnesium status and inflammatory stress in adults older than 51 years with poor quality sleep. Magnes Res, 23(4), 158-168. doi:10.1684/mrh.2010.0220
Cephalon executives have repeatedly said that they do not condone off-label use of Provigil, but in 2002 the company was reprimanded by the FDA for distributing marketing materials that presented the drug as a remedy for tiredness, "decreased activity" and other supposed ailments. And in 2008 Cephalon paid $425m and pleaded guilty to a federal criminal charge relating to its promotion of off-label uses for Provigil and two other drugs. Later this year, Cephalon plans to introduce Nuvigil, a longer-lasting variant of Provigil. Candace Steele, a spokesperson, said: "We're exploring its possibilities to treat excessive sleepiness associated with schizophrenia, bipolar depression, traumatic injury and jet lag." Though she emphasised that Cephalon was not developing Nuvigil as a neuroenhancer, she noted: "As part of the preparation for some of these diseases, we're looking to see if there's improvement in cognition."
Choline is a nootropic: it enhances your ability to pay attention and learn efficiently, probably because you use a lot of acetylcholine during mentally-demanding tasks, and choline helps you synthesize enough to work harder and go longer. Choline also links to decreased brain inflammation in a dose-dependent manner — the more choline you eat, the less inflamed your brain tends to be.
Caffeine keeps you awake, which keeps you coding. It may also be a nootropic, increasing brain-power. Both desirable results. However, it also inhibits vitamin D receptors, and as such decreases the body’s uptake of this-much-needed-vitamin. OK, that’s not so bad, you’re not getting the maximum dose of vitamin D. So what? Well, by itself caffeine may not cause you any problems, but combined with cutting off a major source of the vitamin - the production via sunlight - you’re leaving yourself open to deficiency in double-quick time.
Ginkgo Biloba Leaf(23% extract), Phosphatidylserine 4% Complex(consisting of Lecithin and Phosphatidylserine),N-Acetyl L-Carnitine HCI, St. John's Wort(0.3% extract)(fower heads),L-Glutamine,Dimethylaminoethanol Bitartrate, Bacopa monnieri Leaf Extract(20% bacosides), Vinpocetine(seeds), Huperzine-A(aerial Plant) ; other ingredients: Gelatin(bovine), vegetable magnesium stearate, microcrystalline cellulose and silicon dioxide
Nuts and seeds are terrific sources of vitamin E, which, according to a 2014 study, can help prevent cognitive decline and Alzheimer’s disease as you age. Other vitamin E-rich foods include eggs and cooked veggies. And it’s not just your brain that benefits from nuts; your heart will be happier too. Almonds, walnuts, cashews, Brazil nuts, pistachios, and peanuts have been linked to a decreased risk of cardiovascular disease, according to a Harvard study. Try these other vitamin E-rich foods.
We hope you find our website to be a reliable and valuable resource in your search for the most effective brain enhancing supplements. In addition to product reviews, you will find information about how nootropics work to stimulate memory, focus, and increase concentration, as well as tips and techniques to help you experience the greatest benefit for your efforts.
The effects of piracetam on healthy volunteers have been studied even less than those of Adderall or modafinil. Most peer-reviewed studies focus on its effects on dementia or on people who have suffered a seizure or a concussion. Many of the studies that look at other neurological effects were performed on rats and mice. Piracetam's mechanisms of action are not understood, though it may increase levels of the neurotransmitter acetylcholine. In 2008 a committee of the British Academy of Medical Sciences noted that many of the clinical trials of piracetam for dementia were methodologically flawed. Another published review of the available studies of the drug concluded that the evidence "does not support the use of piracetam in the treatment of people with dementia or cognitive impairment", but suggested that further investigation might be warranted. I asked Seltzer if he thought he should wait for scientific ratification of piracetam. He laughed. "I don't want to," he said. "Because it's working."
I have lots of problems with procrastination and productivity, most likely due to a mild case of ADHD, and recently it's been getting worse and worse. I was a bit hesitant to take Addium at first because I, like most people, had heard about it as a tool for students to use for cramming and it's results sound a little bit like the results of taking Adderall recreationally, which isn't my cup of tea. I was also hesitant to try it because it's marketing just makes it seem like it's a scam pill, and I unfortunately take quality of advertising rather seriously. I changed my mind (after another particularly trying week at work) after a friend of mine actually recommended it for me and told me that she was having great results from it. In my mind, I figured that if a real person,someone I know and trust, tells me in real life that I should maybe try it...then I may as well give it a shot. I ordered the Addium and as soon as I got it, I started taking it immediately. The Addium actually works. I can't believe it. It's helped a lot with my productivity at work. I'm taking just one tablet per day and it seems to be doing the trick. I think the best part about it is that it's not something that you have to continuously take every day.
Along with a great formula, Brainol offers real value in their package deals. Brainol extends discounts of $280 if you order 6 bottles, this is an incredible, sensible, cost saving option. Positive customer feedback and testimonials demonstrate the huge numbers of satisfied customers. Consumers can feel very confident in this brain boosting product as it offers a 100% money-back guarantee. Brainol is formulated in a laboratory that is GMP certified. This means that the company is held to very strict standards and high-quality assurance.
Traditional Chinese medicine also has a long, well-established relationship with nootropic herbs and plants. One of the most popular and well-known is ginkgo biloba, derived from the Chinese maidenhair tree, a relic of the ancient world. The maidenhair tree is the last living species of the division Ginkgophyta>. Some believe that the name ginkgo is a misspelling of the original Japanese gin kyo, meaning “silver apricot”. It’s seen as a symbol of longevity and vitality and is known to be effective at stimulating the growth of new neurons. Researchers have demonstrated that ginkgo flavonoids, the main constituents in ginkgo extract, provide potent anti-Alzheimer’s effects via antioxidant activity in the brains of mice and also stabilize and improve the cognitive performance of Alzheimer patients for 6 months to 1 year. Effective doses range from 120 to 240 mg one to four hours before performance, and for older adults, doses range from 40 to 120 mg three times a day.
Some people consider stimulants to be a form of nootropic, while others distinguish them from the likes of caffeine, and Adderall -- of which there's currently a nationwide shortage. Most legal users of this attention-deficit hyperactivity disorder (ADHD) drug are children; it's prescribed sparingly in adults for fear of abuse. The FDA caused the shortage by halting delivery to drug manufacturers of the drug's active ingredient, an amphetamine, for months, arguing that enough Adderall had already been produced to satisfy all legal demand. The agency argued that abusers of Adderall are responsible for the shortage. That's a group that includes students and professionals using Adderall to help boost productivity during stressful times.
Brain Pill™ combines the most powerful, clinically proven ingredients on the forefront of brain productivity and memory research. Each of our carefully selected ingredients is potent and effective on its own, but together, our research goal was to create far and away the ultimate synergistic combination for enhancing mental clarity, alertness and overall brain function.
Systematic reviews and meta-analyses of clinical human research using low doses of certain central nervous system stimulants found enhanced cognition in healthy people. 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 types of receptor in the prefrontal cortex. Relatively high doses of stimulants cause cognitive deficits.