Nootropic Evidence by Outcome: Alertness, Attention, Memory, Mental Fatigue and Older-Adult Cognition
A plain table of what reviews found for alertness, attention, memory, mental fatigue and older-adult thinking, so you can match a claim to the outcome it was actually tested on.
Content last updated . This page has not been medically reviewed.
The short answer
A good question about any brain supplement is "for which outcome, in whom, compared with what?" This page sorts research by outcome rather than by product. The overall picture from a review of nine ingredients marketed for cognitive performance in healthy adults was low certainty, with studies that are inconsistent, imprecise and often methodologically flawed. [1] Evidence labels (explained in What are nootropics?): evidence in adequately nourished people, promising but limited, mixed, insufficient evidence.Alertness
| Ingredient | What the source found | Label |
|---|---|---|
| Caffeine | Reviewed as enhancing attention and executive functions. [2] It can also disrupt sleep if taken close to bedtime. [3] | Evidence in adequately nourished people (short term) |
See caffeine. No other supplement here has better-supported evidence for alertness.
Attention
| Ingredient | What the source found | Label |
|---|---|---|
| L-theanine | A single 200 mg dose improved choice reaction time in a 31-trial meta-analysis. [4] | Promising but limited |
| Caffeine plus L-theanine | Small differences, wide uncertainty, in the first two hours. [5] | Mixed |
| Bacopa | Shorter choice reaction time in a meta-analysis of nine trials after 12 weeks or more. [6] | Promising but limited |
| Ashwagandha | A 2026 meta-analysis reported improved attention and processing speed. [7] | Promising but limited |
| Citicoline | The Cochrane review of older patients found no benefit on attention. [8] | Not supported in that group |
Memory
| Ingredient | What the source found | Label |
|---|---|---|
| Creatine | A meta-analysis of eight trials found improved memory measures in healthy people, especially ages 66 to 76. [9] See creatine for older adults, women and cognition. | Promising but limited |
| Bacopa | Better free recall on 9 of 17 tests in a review of six trials; little evidence for other abilities. [10] | Promising but limited |
| Ashwagandha | Improved memory (SMD 0.52) in 20 trials with 1,249 people, mixing groups. [7] | Promising but limited |
| L-theanine | No compelling evidence for memory in a review of over-the-counter memory supplements. [11] | Insufficient |
| Lion's mane | Few small trials. [12] | Insufficient |
Mental fatigue and "brain fog"
- L-theanine showed no significant effect on fatigue in the 31-trial meta-analysis. [4]
- "Brain fog" is not a diagnosis; it has many causes, including poor sleep and some medicines. Proper evidence not found for a supplement that treats it: we did not find a systematic review of nootropics for brain fog that we could read. See brain fog and medicines that affect memory.
Older-adult cognition and dementia
These are different questions: keeping thinking sharp in healthy aging, mild cognitive impairment (MCI), and dementia.| Question | What the source found | Label |
|---|---|---|
| Ginkgo to prevent dementia | In 3,069 adults aged 75+, 120 mg twice daily did not reduce dementia or Alzheimer's incidence. [13] | Insufficient evidence |
| Ginkgo in MCI | Cochrane 2026: probably little or no effect at six months. [14] | Insufficient evidence |
| Omega-3 supplements | Several high-quality reviews found no convincing benefit in mild-to-moderate Alzheimer's; see omega-3 evidence by use. [15] | Insufficient evidence |
| Vitamin E | A 2017 Cochrane review found no evidence it prevents progression from MCI to dementia, per NCCIH's summary. [15] | Insufficient evidence |
| Many supplements in AD or MCI | A 2026 network meta-analysis of 29 trials found some gains on one scale but none on another (ADAS-Cog). [16] | Mixed |
| Citicoline | Improved scores in studies of poor quality. [17] | Insufficient evidence |
The National Institute on Aging urges checking with a doctor before trying any pill that promises to prevent Alzheimer's. [18] For habits that do have more support, see brain-healthy habits.
Attention-deficit hyperactivity disorder (ADHD)
ADHD is a medical condition. NCCIH reports that conventional treatment is proven to reduce symptoms in most people, that stimulant medication helps 70 to 80 percent of children with ADHD, and that results for complementary approaches are mixed or have not shown improved symptoms. Despite a lot of research, it is unclear whether omega-3 fatty acids help ADHD. [19] Citicoline and phosphatidylserine reviews in ADHD were heterogeneous. [20] Nootropic supplements are not a replacement for assessment or treatment; see ADHD in adults.Safety
Supplements can interact with medicines and with each other. Read how interactions work and talking with a health professional. For product-specific safety, see safety and claim checks.Frequently asked questions
What is the best supplement for focus?
No supplement has been shown best. Caffeine has the most consistent short-term evidence for attention; L-theanine and bacopa show small effects in some trials. [2][4][6]
What supplements help memory?
Creatine, bacopa and ashwagandha show promising but limited results on memory tests; certainty is low. [9][10][7]
Do supplements help brain fog?
Proper evidence not found; see brain fog.
Do supplements prevent dementia?
No supplement has been proven to. [18]
Do supplements treat ADHD?
NCCIH says results for complementary approaches are mixed or unproven; stimulant medication helps most children. [19]
References
- Crawford C et al. J Altern Complement Med 2021. Dietary Supplement Ingredients for Optimizing Cognitive Performance Among Healthy Adults: A Systematic Review. Read 2026-10-22.
- Lorca C et al. Crit Rev Food Sci Nutr 2023. Plant-derived nootropics and human cognition: a systematic review. Read 2026-10-22.
- Bagheri Davisaraei Y et al. Prog Brain Res 2024. Coffee and sleep: Benefits and risks. Read 2026-10-22.
- Gerolymos C et al. Mol Psychiatry 2026. Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials. Read 2026-10-22.
- Payne ER et al. Nutr Rev 2025. Effects of tea (Camellia sinensis) or its bioactive compounds l-theanine or l-theanine plus caffeine on cognition, sleep, and mood in healthy participants: a systematic review and meta-analysis of randomized controlled trials. Read 2026-10-22.
- Kongkeaw C et al. J Ethnopharmacol 2014. Meta-analysis of randomized controlled trials on cognitive effects of Bacopa monnieri extract. Read 2026-10-22.
- Zhu X et al. Front Pharmacol 2026. Effects of Withania somnifera (L.) Dunal (Ashwagandha) on cognitive and physical function in adults: a systematic review and meta-analysis. Read 2026-10-22.
- Fioravanti M, Yanagi M. Cochrane Database Syst Rev 2005. Cytidinediphosphocholine (CDP-choline) for cognitive and behavioural disturbances associated with chronic cerebral disorders in the elderly. Read 2026-10-22.
- Prokopidis K et al. Nutr Rev 2023. Effects of creatine supplementation on memory in healthy individuals: a systematic review and meta-analysis of randomized controlled trials. Read 2026-10-22.
- Pase MP et al. J Altern Complement Med 2012. The cognitive-enhancing effects of Bacopa monnieri: a systematic review of randomized, controlled human clinical trials. Read 2026-10-22.
- Hersant H et al. CNS Drugs 2023. Over the Counter Supplements for Memory: A Review of Available Evidence. Read 2026-10-22.
- Menon A et al. Front Nutr 2025. Benefits, side effects, and uses of Hericium erinaceus as a supplement: a systematic review. Read 2026-10-22.
- DeKosky ST et al. JAMA 2008. Ginkgo biloba for prevention of dementia: a randomized controlled trial. Read 2026-10-22.
- Wieland LS et al. Cochrane Database Syst Rev 2026. Ginkgo biloba for cognitive impairment and dementia. Read 2026-10-22.
- NCCIH, Dietary Supplements and Cognitive Function, Dementia, and Alzheimer's Disease: What the Science Says (July 2022). Read 2026-10-22.
- Li Y et al. Nutr Neurosci 2026. The impact of supplements on cognitive function for Alzheimer's disease or mild cognitive impairment: a systematic review and network meta-analysis. Read 2026-10-22.
- Bonvicini M et al. Nutrients 2023. Is Citicoline Effective in Preventing and Slowing Down Dementia? A Systematic Review and a Meta-Analysis. Read 2026-10-22.
- National Institute on Aging, Preventing Alzheimer's Disease: What Do We Know?. Read 2026-10-22.
- NCCIH, Attention-Deficit Hyperactivity Disorder at a Glance. Read 2026-10-22.
- Kucuksahin NG et al. Hum Psychopharmacol 2026. The Impact of Citicoline/Phosphatidylserine Supplementation on Cognitive Performance and Executive Functions in Mental Disorders: A Systematic Review of Controlled Trials. Read 2026-10-22.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.