Supplements for Stress and Anxiety — What the Evidence Shows (UK)

Best supplements for stress and anxiety: what works?

The honest answer is: a handful of compounds have decent human trial data behind them, and most of the rest are extrapolating from rodent studies or tiny pilot trials. Ashwagandha has the strongest evidence - a 2019 RCT in 60 adults showed a 27.9% reduction in serum cortisol versus placebo. But dose, extract quality, and your baseline stress load all matter enormously. Here's what the research actually says.

What the evidence actually shows

I want to be direct about something before we get into individual compounds: the best supplements for stress and anxiety UK conversation is frequently hijacked by marketing language that papers over enormous gaps in the evidence. So let me give you the actual picture.

The most replicated findings centre on a small group of adaptogens and amino acids. Ashwagandha (Withania somnifera) root extract is the standout. In a double-blind RCT by Chandrasekhar et al. (2012) involving 64 adults with a history of chronic stress, the high-concentration ashwagandha group showed a statistically significant reduction in perceived stress scores (PSS) of 44% versus 5.5% in the placebo group (p<0.001), along with a 27.9% reduction in serum cortisol. That's a meaningful effect size in a properly controlled trial.

L-theanine, an amino acid found naturally in green tea, also has reasonable human data. A crossover RCT by Kimura et al. (2007) in 16 healthy adults found that 200mg L-theanine attenuated heart rate and salivary immunoglobulin A responses to an acute stress task, suggesting a genuine physiological effect on the stress response - not just a subjective feeling of calm.

Magnesium is worth mentioning here too, though I'd frame it differently. A 2017 systematic review by Boyle et al. (2017) covering 18 studies concluded that magnesium supplementation likely benefits subjective anxiety in mildly anxious individuals, particularly those who are deficient. The caveat: many of the included studies were methodologically weak. If you're eating a varied diet, you may not be deficient. If you're under chronic stress, you probably are - stress depletes magnesium through urinary excretion.

What's biologically happening: the cortisol and HPA axis story

Stress isn't just a feeling. It's a cascade. The hypothalamic-pituitary-adrenal (HPA) axis is the central regulatory system. When you perceive a threat - a deadline, a difficult conversation, a near-miss in traffic - the hypothalamus releases corticotropin-releasing hormone (CRH). That signals the pituitary to release ACTH, which tells the adrenal glands to produce cortisol.

Cortisol in short bursts is functional. It mobilises glucose, sharpens attention, suppresses inflammation temporarily. The problem is chronic activation. Sustained elevated cortisol impairs hippocampal neurogenesis, disrupts sleep architecture, suppresses immune function, and dysregulates the very feedback mechanisms designed to switch the system off. You end up with a HPA axis that's stuck in a semi-activated state.

This is where adaptogens are theorised to act - not by blocking the stress response entirely, but by modulating it. Ashwagandha's active constituents, the withanolides, appear to interact with GABA-A receptors and reduce HPA axis hyperactivity. Rhodiola rosea's active compounds (rosavins and salidroside) are thought to influence monoamine neurotransmitter systems, particularly serotonin and dopamine. The mechanistic picture is plausible. But I'd be overstating it to claim we fully understand the pathways in humans - much of this is inferred from animal models and in vitro work.

Separately, certain nutrients play direct roles in stress physiology. Vitamin C is concentrated in the adrenal glands and is consumed rapidly during cortisol synthesis. There's a reason the adrenals hold some of the highest concentrations of vitamin C in the body. The claim that Vitamin C contributes to the reduction of tiredness and fatigue is authorised under UK nutrition regulations, and the underlying biology - its role in mitochondrial energy metabolism and adrenal function - is well established.

Dosing: what clinical trials actually used

This matters more than most supplement brands want you to know. A compound tested at 600mg in an RCT is not the same as 50mg sprinkled into a blend. If you want to read more about how brands obscure this, I wrote about it here: why supplement labels lie.

Here's what the clinical literature supports for the main compounds:

• Ashwagandha (KSM-66 or Sensoril extract): 300-600mg/day of root extract standardised to ?5% withanolides. The Chandrasekhar 2012 trial used 300mg twice daily. A 2019 RCT by Langade et al. (2019) used 300mg twice daily and found significant improvements in sleep quality and morning cortisol in 58 participants.
• L-theanine: 100-400mg/day. Most acute stress trials use 200mg as a single dose. Chronic supplementation data is thinner.
• Magnesium: 300-400mg elemental magnesium/day. Glycinate and malate forms tend to have better tolerability than oxide. The Boyle review used a wide range of forms and doses, which is part of why the evidence is messy.
• Rhodiola rosea: 200-600mg/day of extract standardised to 3% rosavins and 1% salidroside. A 2009 RCT by Olsson et al. (2009) in 60 adults with stress-related fatigue found significant improvements in burnout symptoms versus placebo at 576mg/day.
• Vitamin C: 500mg/day is a well-studied dose for adrenal support and general antioxidant function. This is the dose in Kojo's formula, and it sits comfortably within the range used in trials examining cortisol and oxidative stress markers.

Glycine is worth a mention here. At 3,000mg/day, it's been studied for sleep quality - and poor sleep is both a cause and consequence of chronic stress. A trial by Inagawa et al. (2012) in 11 participants found that 3g glycine before bed improved subjective sleep quality and reduced daytime sleepiness. The sample size is small, and large-scale human trials are limited, so I'd treat this as promising rather than settled. Research is ongoing.

Ashwagandha: the most evidence-backed option

I've covered this in more depth elsewhere - if you want the full picture, the ashwagandha benefits piece goes through the primary literature properly. But the summary for stress and anxiety specifically:

The 2019 study by Langade et al. (2019) is one of the cleaner trials. 58 adults with self-reported poor sleep and stress were randomised to 300mg ashwagandha root extract twice daily or placebo for 8 weeks. The treatment group showed statistically significant improvements in sleep onset latency, sleep efficiency, and morning serum cortisol (p<0.05 for all). The effect on anxiety, measured by the Hamilton Anxiety Rating Scale, was also significant.

A more recent meta-analysis by Pratte et al. (2021) pooled data from 5 RCTs (n=400) and found a standardised mean difference of -0.79 (95% CI: -1.12 to -0.45) for anxiety outcomes - a moderate-to-large effect size by conventional benchmarks. That's meaningful. It's also worth noting that the trials were mostly short (8-12 weeks) and in adults with mild-to-moderate stress, not clinical anxiety disorders.

Ashwagandha is generally well tolerated at these doses. Gastrointestinal discomfort is the most commonly reported side effect. There are rare case reports of liver injury at very high doses, but these are not well-established at standard supplementation doses. As always, if you're on thyroid medication or immunosuppressants, check with your GP - ashwagandha appears to influence thyroid hormone levels in some individuals.

The compounds with thinner evidence

I want to be honest about the parts of this category where the human data is genuinely weak.

Taurine

Taurine has an interesting mechanistic profile - it modulates GABA receptors and has demonstrated anxiolytic effects in rodent models. A study by Kong et al. (2006) showed taurine reduced anxiety-like behaviour in mice via GABA-A receptor activation. The human data on taurine for stress and anxiety specifically is thin, and I'd be overstating it to claim otherwise. Research is ongoing, and I'd frame taurine as a compound with a plausible mechanism rather than proven human benefit for stress.

Pine bark extract

Pycnogenol (French maritime pine bark extract) has been studied for cognitive function and oxidative stress. A 2012 study by Trebatick� et al. (2012) found improvements in attention and oxidative stress markers in children with ADHD - not directly applicable to adult stress. The anti-inflammatory and antioxidant properties are reasonably well evidenced, but specific anxiety data in humans is limited. Large-scale human trials are lacking.

Aged garlic extract

Aged garlic extract (AGE) has the best evidence in cardiovascular and immune contexts. Its relevance to stress is indirect - chronic stress drives oxidative damage and inflammation, and AGE has demonstrated antioxidant activity in several human trials. But if someone asks me whether AGE is a stress supplement, I'd say no, not directly. The research is ongoing and the stress-specific human data is limited.

What about B vitamins and adaptogens together?

A common formulation approach is to combine B vitamins (particularly B5, B6, B12) with adaptogenic herbs, on the basis that B vitamins support adrenal function and neurotransmitter synthesis. The rationale is sound in principle. Vitamin B5 (pantothenic acid) is a precursor in the synthesis of coenzyme A, which is required for cortisol production. B6 is a cofactor in serotonin and dopamine synthesis.

A 2019 RCT by Smith et al. (2019) in 478 adults found that a combination of B vitamins significantly reduced work-related stress scores versus placebo over 30 days, with particularly strong effects in those with high baseline stress. Effect sizes were modest but statistically significant (p=0.02). This is one of the larger trials in this space and worth taking seriously.

The combination approach - addressing multiple pathways simultaneously - is theoretically appealing. But it also makes it harder to know what's actually working. If you're trying to understand your own response, isolating variables matters.

Who actually benefits: baseline matters enormously

This is something I don't see discussed enough. The evidence for most of these compounds is strongest in people with elevated baseline stress or subclinical deficiency. If your cortisol is already well-regulated and you're sleeping fine, the effect size you'll notice from ashwagandha or magnesium is likely to be small.

Conversely, if you're genuinely under chronic load - poor sleep, high cognitive demand, irregular eating, significant life stressors - the data suggests these compounds can make a measurable difference. The Chandrasekhar 2012 trial enrolled adults with "a history of chronic stress." The Olsson 2009 Rhodiola trial recruited people with "stress-related fatigue." These are the populations where the effects were demonstrated.

I say this not to discourage anyone, but because I think it's more useful than telling everyone they need a stress stack regardless of context. If your stress is situational and time-limited, lifestyle factors - sleep, exercise, social connection - will almost certainly outperform any supplement. If it's chronic and entrenched, supplementation may genuinely help as an adjunct. It's not a replacement for addressing root causes.

For a broader overview of how I think about this category, the supplements for stress and anxiety piece covers the evidence landscape in more detail.

Frequently asked questions

My honest take

I started looking seriously at this category because I was under a sustained period of high stress a few years ago - building a business, not sleeping well, running on caffeine and stubbornness. I read the primary literature because I didn't trust the marketing, and I found something genuinely useful: a small group of compounds with real human trial data, sitting inside a much larger category of things sold with claims they can't support.

Ashwagandha is the one I'd point to first, with the strongest caveat that extract quality and dose matter enormously. Most high-street products are underdosed or use unspecified extracts with no withanolide standardisation. L-theanine is worth considering if your stress manifests as acute reactivity rather than chronic fatigue. Magnesium is probably worth addressing if you're not confident you're getting enough through diet - most people in the UK aren't.

I'm genuinely uncertain about some of the other compounds in this space. Taurine's mechanistic story is interesting. Glycine's sleep data is promising. But "interesting and promising" is not the same as "proven," and I'd rather tell you that directly than dress up uncertainty as confidence.

What I'm most certain about is this: no supplement addresses the structural causes of chronic stress. Work pressure, financial strain, relationship difficulty, poor sleep habits - these require solutions that aren't sold in capsules. The compounds I've described here are adjuncts at best. Useful ones, in some cases. But adjuncts.

If you want to understand exactly what's in the Kojo formula and why each ingredient is dosed the way it is, that information is on the product page. No proprietary blends. No hidden doses. Just the numbers.