science9 min readエビデンス確認日： 2026年9月28日

How Nootropics Work: Mechanisms of Action Explained

A science-based breakdown of how different nootropic ingredient classes work in the brain — from acetylcholine to NGF to the HPA axis.

The cholinergic system

Acetylcholine is the primary neurotransmitter for attention, learning, and memory encoding. The cholinergic pathway runs from the basal forebrain to the hippocampus and cortex — the exact brain regions involved in forming new memories and sustaining focus. Nootropics enhance cholinergic function in three ways: (1) providing choline precursors (Citicoline, Alpha-GPC, choline bitartrate) that the brain converts to acetylcholine; (2) inhibiting acetylcholinesterase, the enzyme that breaks acetylcholine down — well established in humans for Huperzine A, whereas for Bacopa it is one of several proposed mechanisms, supported mainly by animal data; or (3) increasing the sensitivity of acetylcholine receptors. This is why many premium stacks contain both a choline source and a cholinesterase inhibitor.

The dopaminergic system

Dopamine drives motivation, reward, and working memory. L-Tyrosine is the amino acid precursor that the brain converts to L-DOPA and then dopamine. Under stress, sleep deprivation, or cognitive overload, dopamine and norepinephrine stores are depleted faster than the brain can replenish them — resulting in reduced motivation, poor working memory, and cognitive fatigue. Tyrosine supplementation replenishes the substrate, maintaining performance when conditions are demanding. Adaptogens like Rhodiola Rosea modulate dopamine availability by inhibiting monoamine oxidase (MAO).

The HPA axis and cortisol

The hypothalamic-pituitary-adrenal (HPA) axis governs the stress response. Chronic stress elevates cortisol, which damages hippocampal neurons over time, impairs memory consolidation, and reduces cognitive flexibility. Adaptogens — including Ashwagandha (KSM-66), Rhodiola Rosea, and Panax Ginseng — regulate HPA axis activity, blunting cortisol secretion under acute stress and reducing baseline cortisol over several weeks of use. This is why adaptogens are considered long-term cognitive protectants rather than acute enhancers. They are not a substitute for clinical care for diagnosed anxiety or stress-related conditions.

Nerve Growth Factor (NGF) and neurogenesis

Nerve Growth Factor is a protein that promotes the growth, maintenance, and survival of neurons. NGF production declines with age, contributing to memory loss and slower cognitive processing. Lion's Mane mushroom contains hericenones (in the fruiting body) and erinacines (in the mycelium), compounds that stimulate NGF synthesis in the brain. This is why Lion's Mane is one of the few nootropic ingredients with legitimate neuroregeneration potential — though the effects are cumulative and require weeks to months of supplementation to measure.

Alpha brain waves and calm focus

Alpha brain waves (8–12 Hz) are associated with relaxed alertness — the mental state experienced during flow states, meditation, or creative work. L-Theanine, an amino acid from green tea, increases alpha-wave activity: in EEG studies the increase appears from around 45 minutes after ingestion, and a 2021 RCT found the clearest effect about 3 hours after a 200mg dose. This produces a state of calm focus without sedation. When combined with caffeine, L-theanine can blunt some of the anxiogenic (anxiety-inducing) effects of caffeine while preserving its attention-sharpening and reaction-time benefits, a pairing with reasonable support from multiple RCTs.

Cell membrane integrity and phospholipids

Neuronal cell membranes are composed largely of phospholipids — primarily phosphatidylserine (PS) and phosphatidylcholine. Healthy membranes are essential for efficient signal transmission between neurons. PS levels in the brain decline with aging. Supplementing with PS replenishes membrane composition, improving synaptic signal transduction and facilitating neurotransmitter release. Citicoline works similarly — as a precursor to phosphatidylcholine, it supports membrane repair while simultaneously boosting acetylcholine synthesis.

Nootropics in Japan

In Japan, whether a supplement is allowed to describe how it works comes down to whether a business has notified the CAA of the scientific evidence behind that mechanism. The CAA's Foods with Function Claims system lets a business state a function once it has filed that evidence, but the agency itself does not verify it — the government does not conduct an examination (our translation) MHLW's own review of overseas products marketed as improving brain function found a different problem in that market: many of the products were found to claim that they contained ingredients used in prescription medicines.

A function claim rests on the notifier's own evidence

The CAA describes its Foods with Function Claims framework as a system where a business notifies the Commissioner of the Consumer Affairs Agency of the necessary matters, such as scientific evidence on the safety and function of the food, before sale (our translation), and can then display that function. The same source is explicit that, unlike FOSHU, the government does not conduct an examination (our translation) of that evidence — so a mechanism claim on a Japanese label reflects the filing business's own scientific dossier, not an independent government finding.

Why some 'brain function' products turned out to be something else

MHLW's investigation into overseas medicines and supplements marketed as enhancing brain function found that many of them claimed to contain ingredients used in prescription medicines (our translation) while being sold and described as food or supplement products. That finding is why MHLW now requires an import confirmation for specific named ingredients regardless of quantity — the concern was not a nootropic's ordinary mechanism of action, but that self-administered pharmaceutical-grade compounds carried a real risk of health harm without medical supervision.

Products in Japan

Consumer Affairs Agency (FFC)

If a Japanese supplement label describes how it improves cognitive function, has that mechanism been independently verified?

Not by the government. Under the CAA's Foods with Function Claims system, a business displays the claim after notifying the agency of its supporting evidence, but the CAA states the government does not conduct an examination (our translation) — verification is the notifying business's own responsibility, not an independent scientific review.

Why did MHLW investigate overseas 'brain function' products specifically?

MHLW's own inquiry found that products marketed abroad as enhancing brain function in many cases claimed to contain ingredients used in prescription medicines (our translation), which is a materially different regulatory situation from a food-grade nootropic ingredient and is why a specific ingredient list now requires advance import confirmation.

Prefecture guides

Sources: Consumer Affairs Agency (CAA) — 機能性表示食品について (About Foods with Function Claims) · MHLW (Kinki Regional Bureau of Health and Welfare) — 脳機能の向上等を標ぼうする医薬品等を個人輸入する場合の取扱いについて (Handling of personal imports of medicines etc. claiming to enhance brain function)

Regulatory note

本ページは教育目的の編集コンテンツであり、医学的助言を構成するものではありません。日本国内で販売される機能性表示食品（FFC）および特定保健用食品（FOSHU）は、消費者庁への届出または許可を必要とします。届出のない輸入品については、日本の薬機法（旧薬事法）の下で疾病治療を示唆する表現は規制されます。サプリメントを開始する前に、必ず資格のある医療専門家にご相談ください。This page is editorial and not medical advice. Foods with Function Claims (FFC) and Foods for Specified Health Uses (FOSHU) sold in Japan require notification or approval from the Consumer Affairs Agency. Imported products without notification cannot make disease-treatment claims under the Pharmaceuticals and Medical Devices (PMD) Act. Note: In July 2026, the Consumer Affairs Agency (CAA) opened a public comment period (Notice No. 235080088, closes 30 July 2026) on proposed revisions to permitted claim wording for FFC-notified ingredients including DHA, phosphatidylserine, and NMN; compliant claim language may require updating once the final Cabinet Office Order is published. Consult a qualified healthcare professional before starting any supplement.

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