What the science actually says about nootropics, adaptogens and cognitive support compounds.
About one in twenty adults in Europe has a contact allergy to fragrance materials. Among people already attending a dermatology clinic with dermatitis, sensitisation to the standard fragrance marker runs to roughly one in five.
Taurine is in almost every energy drink and in a great many supplements, on the strength of findings that mostly did not test taurine.
Methylsulfonylmethane has a real human evidence base. It is about knees.
Rhodiola rosea is sold on a claim about fatigue, and it is one of the botanicals where the extract specification matters more than the plant name. Two grams of a herb standardised one way is not the same product as two grams standardised another.
Vitamin B3 comes in forms that behave differently enough to confuse people who have read one thing and bought another. The flushing that niacin is famous for comes from one of them and not the others.
Omega-3 supplements are the best-selling ingredient in the cognitive category, and a 2025 dose-response meta-analysis of 58 randomised trials reports effects on cognition larger than anything else this library has covered.
Citicoline is the most clinically studied compound in our Clarity formulation, and it is the one with the most uncomfortable evidence. Two large trials designed to settle its value in acute brain injury returned negative results, and interest in the compound continued anyway.
Uridine is the most open question in our Clarity formulation. The mechanistic case is elegant and comes largely from animals; the human case rests on trials of a multinutrient product designed around the same hypothesis.
Acetyl-L-carnitine has been studied in cognitive disorders for more than thirty years, which is long enough that the shape of the evidence has become clear. It is a shape worth recognising, because it recurs across this whole category.
Magnesium is the only compound in our formulations that carries authorised health claims, which makes it the one we are allowed to talk about — and, for exactly that reason, the one where the temptation to overstate is greatest.
Nootropics are a commercial category before they are a scientific one. The word covers prescription stimulants, Soviet-era synthetics, herbal extracts and vitamins, grouped by what they are sold to do rather than by what they are.
Between 2023 and 2024 three randomised placebo-controlled trials tested single cognitive supplements in healthy adults: alpha-GPC, ashwagandha, and a comparison of guayusa extract with lion's mane. All are recent, all are properly designed, and all report positive findings.
Reviews of nootropics generally conclude that side effects are uncommon and rarely serious. That generalisation holds for herbal extracts at ordinary doses and fails completely for at least one compound sold in the same aisle.
L-theanine is an amino acid that makes up nearly half the free amino acids in green tea. In the last five years it has accumulated systematic reviews and meta-analyses faster than almost any other compound in its category, and those reviews do not agree with each other.
In February 2025 a team of Australian academics published a meta-analysis of L-theanine and sleep. In November 2025 a second team published a systematic review of the same question, drawing on a heavily overlapping set of trials.
Every review in this series leans on the same background assumption: that L-theanine's effect on stress is the well-established part, and that its effects on attention and sleep may follow from it. The stress literature is where the compound is supposed to be strong.
The first three parts of this series covered what L-theanine has been tested for in healthy adults: attention, sleep, stress. This part covers what it has been shown to do everywhere else — in immunity, in the gut, and in developing neurons.
In February 2025, Roderick Dashwood and Francesco Visioli published a review in Nutrition Research whose title asks the question this series has been circling: does the science match the hype for brain health and relaxation?
In South Korea several compounds sold elsewhere as supplements are prescription medicines, and doctors routinely add them to standard dementia treatment. That produces something rare: a large body of real-world data on whether the addition helps.
Tualang honey is produced by giant honeybees nesting in a single species of Malaysian rainforest tree, and it has accumulated a decade of neurological research — enough for a dedicated review in 2021.