Chamomile and Passion Flower for Anxiety: What the Trials Actually Found

Chamomile and passion flower are the two herbs most often sold for anxiety, and unlike much of the calming aisle they have actually been tested in people with a diagnosed anxiety disorder.

This piece has one job: compare the doses used in the research against the doses in our own product. That comparison does not flatter us, which is why it's here. If you want the fuller evidence review of each ingredient on its own terms, we have those separately — chamomile and passion flower — and they go deeper into the sleep data than this page does.

Chamomile: what the trials found

The short randomised trial

A double-blind, placebo-controlled trial of oral chamomile extract in 57 people with mild to moderate generalised anxiety disorder, over 8 weeks, using the Hamilton Anxiety Rating Scale.

Result: a significantly greater reduction in total HAM-A score than placebo (p=0.047). A genuine positive result in a properly blinded design — and at p=0.047 it clears the conventional threshold by a margin slim enough that the investigators themselves called it modest anxiolytic activity. That is the honest characterisation and we're not going to improve on it.

The long-term trial, reported properly

This is the one usually cited as chamomile's strongest evidence, and it's worth stating what it actually showed rather than only how well it was designed.

179 participants took pharmaceutical-grade chamomile extract at 1,500 mg/day (three 500 mg doses) for a 12-week open-label phase. Just over half responded well enough to enter a 26-week double-blind, placebo-controlled continuation, where responders were either kept on chamomile or switched to placebo. A 26-week controlled phase is unusually long for any herbal anxiolytic.

And the result:

• Relapse was 15.2% on chamomile versus 25.5% on placebo — and that difference did not reach statistical significance.
• What was significant: people who stayed on chamomile had meaningfully lower GAD symptom scores across the follow-up than those switched to placebo, with secondary improvements in body weight and blood pressure.

So the fair summary is: long-term chamomile was safe and reduced symptoms, but was not shown to prevent relapse. An earlier version of this article described the trial's design without reporting the non-significant relapse result, which made chamomile look stronger than the data supports. That was our error and this is the correction.

Why apigenin, and why that's not proof

Apigenin is the flavonoid usually credited with chamomile's effect, and the proposed mechanism is binding at benzodiazepine sites on the GABA-A receptor — the same broad family of sites benzodiazepines act on, at far lower potency. It's why standardised extracts are measured against apigenin content rather than just "chamomile."

That story is plausible and mostly built from laboratory work. A mechanism demonstrated in a receptor preparation is not an effect demonstrated in a person, and the mechanism is interesting precisely because the clinical evidence is thin enough to need supporting. Treat it as a reason the trials were worth running, not as evidence in its own right.

Passion flower: one notable trial, and a thin field

The most-cited study is a double-blind randomised trial in 36 people with generalised anxiety disorder over 4 weeks, comparing 45 drops daily of a Passiflora incarnata liquid extract against 30 mg of oxazepam, a benzodiazepine.

Result: comparable anxiolytic efficacy, with significantly less impairment of job performance in the passion flower group.

There is something real in that — the cognitive dulling of a benzodiazepine is a genuine cost. But the trial has a limitation that changes how much weight it carries, and it's easy to miss.

There was no placebo arm. Both groups received an active treatment, so "comparable efficacy" tells you the two did about the same thing — not that either beat placebo. In a condition that responds substantially to placebo over four weeks, that is not a small gap in the design.

And the wider field is small. A 2020 systematic review of Passiflora incarnata in neuropsychiatric conditions found only one of roughly nine randomised trials enrolled patients with formally diagnosed GAD — the rest looked at preoperative or situational anxiety, sleep quality or cognition. Samples ran from 16 to 128 people, extract types and doses varied, and the heterogeneity was such that the authors could not pool the results into a meta-analysis. Promising is fair. Settled is not.

How our own product compares

This is the part that matters if you're reading this because you were thinking of buying something.

Proco's Sleep Formula is the one product in our range with every ingredient individually dosed and disclosed, and two of those ingredients are the ones above.

Those are not the same interventions. The chamomile gap is fifteen-fold against the GAD trial dose and four-fold against the lower sleep-trial dose — and it isn't only quantity: the research used a specific standardised extract, and we are not in a position to claim ours matches that preparation. Passion flower sits at the bottom of, or below, the range used in the sleep trials.

One further honesty point about the passion flower comparison: the GAD trial's dose was 45 drops of a liquid extract, and a drop count doesn't convert cleanly to a milligram weight. Where a trial reports a dose in a form that can't be translated to a capsule, any product claiming to deliver "the studied dose" is guessing.

This is the same problem in a different costume from one we've written about before: how to read a supplement label, and how underdosing hides in plain sight. The difference here is that we're applying it to ourselves.

So why are these ingredients in the product at all?

A fair question, and it deserves a direct answer.

Sleep Formula is a sleep product, not an anxiety treatment. The doses are in the range normally used in sleep blends, where the intended effect is mild and the ingredients work alongside each other rather than one carrying the result. A formula's job is balancing several ingredients rather than maxing out any single one. That is a legitimate thing for a supplement to be.

What it is not is the intervention in the trials above. If you read about a chamomile trial in generalised anxiety disorder and bought our product expecting that result, you would not be getting it, and we would rather say so on our own website than let the association do quiet work for us.

Two further limits. These trials ran in people with a diagnosed anxiety disorder, under clinical supervision, with clinician-rated outcomes. A supplement is not a treatment for an anxiety disorder, ours included. And a positive trial of one standardised extract does not transfer to every product containing the same plant.

Safety, which is not nothing

Chamomile is in the Asteraceae family, alongside ragweed, daisies, chrysanthemums and marigolds — so people with those allergies have a meaningfully higher risk of reacting to it, including rare serious hypersensitivity reactions. It also interacts with warfarin: there is a published case report of a raised INR in a long-term chamomile tea drinker on warfarin. If you're on an anticoagulant, this is a doctor conversation before any form of chamomile.

Passion flower is sedating, and that effect is additive with alcohol, benzodiazepines, sleep medication and other sedating drugs. Mild drowsiness is the most commonly reported side effect; dizziness and confusion occasionally. It should be avoided in pregnancy, since it may stimulate uterine contractions, and its safety in breastfeeding hasn't been established. Don't drive on a first dose you haven't taken before. On alcohol specifically, we've set out where our own products stand.

If you take psychiatric medication, check the combination before adding anything — the interactions across our range are listed here.

And one specific to our range: Sleep Formula contains 2 mg of melatonin and Sleep Support contains 10 mg. Do not take both the same night — that's 12 mg combined, around three times the dose at which the dose-response research suggests the effect plateaus. More melatonin is not more sleep.

What has better evidence than either of these

If anxiety is the actual problem, the interventions with the strongest evidence are not in this article and not in our range: cognitive behavioural therapy, and the SSRI and SNRI medications, both with a trial base a 36-person pilot can't be compared to. Exercise has a genuine and growing evidence base too. We've ranked the options by how well supported they are.

Among the other botanicals, magnesium is thinner than its reputation, and hops rests on a single 36-person crossover trial — both written up at their actual size rather than their marketing size.

And before any of that, be clear what you're treating. Anxiety as a normal response and anxiety as a disorder are different things with different answers — the distinction is here. One medical cause worth excluding specifically: an overactive thyroid produces anxiety, tremor, palpitations and insomnia, and is frequently treated as an anxiety disorder for a long time first. That's a single blood test.

This article is not medical advice, and nothing in Proco's range is a treatment for an anxiety disorder. If anxiety is affecting your daily life, speak to a doctor. Do not stop or change prescribed medication on the basis of anything here.

Sources: Amsterdam et al., randomised placebo-controlled chamomile extract in GAD (2009) · Mao et al., long-term chamomile treatment for GAD, randomised clinical trial (2016) · Akhondzadeh et al., passionflower vs oxazepam in generalised anxiety (2001) · Janda et al., Passiflora incarnata in neuropsychiatric disorders — a systematic review (2020)