Supplements and calm
Silexan lavender capsules for anxiety: what the trials found, and what to check first
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed October 20266 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
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Silexan is a lavender oil capsule, sold in the UK as Kalms Lavender One-A-Day at 80 mg. Five placebo-controlled trials found it eased anxiety more than a dummy pill over ten weeks. Before you take it, rule out the physical causes that feel the same, starting with your thyroid and B12.
Anxious and not sure why? Find my test →As of October 2026. Searches for Silexan have climbed sharply this year. The main evidence behind the buzz is a 2023 review of every placebo-controlled trial, published in the European Archives of Psychiatry and Clinical Neuroscience.
A racing heart, a knot in your stomach, nights spent wide awake. It is natural to reach for something gentle and herbal. Lavender capsules may well help. But some of that feeling has a cause a blood test can find.
1. What is Silexan?
Silexan is an oil pressed from the flowers of true lavender, made to a fixed recipe so every capsule matches. You swallow it. It is not the same as sniffing an essential oil or rubbing it on your wrists.
In the UK, the version you will find in most chemists is Kalms Lavender One-A-Day. Each capsule holds 80 mg of lavender oil, the dose used in the trials. It is licensed as a traditional herbal medicine for “the temporary relief of the symptoms of mild anxiety such as stress and nervousness, based on traditional use only.” That wording matters. It is for mild, passing anxiety, not an anxiety disorder.
2. What else feels like anxiety?
Anxiety is a feeling, not a diagnosis. Usually it is stress. Sometimes it is your body. The most common physical cause is an overactive thyroid, the gland in your neck that sets how fast your body runs. The NHS lists “nervousness, anxiety and irritability” and palpitations among its symptoms, then adds:
“These symptoms and signs can have a number of causes. But a blood test can often help to determine whether they’re caused by a thyroid problem.”
NHS, Overactive thyroid symptoms
Low vitamin B12 is the other one to know. B12 is the vitamin your nerves and red blood cells need to work. The NHS says a shortage can cause “psychological problems, which can range from mild depression or anxiety, to confusion and dementia”.
You cannot feel the difference between stress and a thyroid running hot. A lavender capsule may soften either one, and that is the problem. It can quiet the signal while the cause carries on. Our guide to anxiety and blood tests covers every physical cause worth ruling out.
3. Does Silexan actually work?
The trials say yes, modestly. The 2023 review pooled all five double-blind trials, with 1,213 adults taking 80 mg or a dummy pill each day for ten weeks. Silexan beat the dummy pill on the Hamilton Anxiety Rating Scale, a standard anxiety score a clinician fills in after an interview.
People on Silexan were 1.34 times as likely to see their anxiety score halve. Self-rated anxiety and quality of life improved too. Side effects were no more common than on the dummy pill.
Two honest caveats. Every trial was funded by the German firm that makes Silexan, and one review author works for it. And the trials covered mild to moderate anxiety. Nobody has shown it can replace a prescribed medicine, so never swap one for the other without your prescriber.
4. Side effects and who should avoid it
The side effect people talk about is burping. A 2019 analysis of the trials found lavender-tasting burps or breath in 7 to 20% of people on Silexan, against none on placebo. Nausea and loose stools also came up. No serious side effects were linked to it.
The Kalms leaflet says not to take it if you:
- are under 18, pregnant or breastfeeding.
- take other medicines for anxiety or that make you sleepy.
- have, or have ever had, liver problems.
It may also affect driving, so see how it suits you first. If low mood has lasted for weeks, speak to a qualified clinician rather than treating it yourself.
5. What to check before you start
A handful of markers cover the physical side of anxiety.
- TSH and Free T4. TSH is the signal that tells your thyroid how hard to work, and Free T4 is the hormone it makes.
- Vitamin B12. A shortage can show up as low mood or anxiety before anything else.
- Cortisol. Your main stress hormone, best read from a morning sample.
- Vitamin D and magnesium. Two nutrients people often take for mood, worth seeing before you add more.
Helvy’s General Energy & Wellness panel (£149) reads all of these from one home finger-prick sample, at UKAS-accredited UK laboratories. If thyroid is your main worry, start with our thyroid hub.
Clear results make lavender a sensible, low-risk thing to try. It is the same logic as magnesium for anxiety: measure, then try. If tiredness is the bigger issue, our tired-all-the-time guide walks through every testable cause.
READY TO TEST?
See whether it’s stress, or something testable
Helvy’s home blood tests report thyroid, B12, cortisol and vitamin D with clear context. Results in about 5 working days from UKAS-accredited UK laboratories.
Frequently asked questions
Is Kalms Lavender the same as Silexan?
Kalms Lavender One-A-Day contains 80 mg of lavender oil per capsule, the same daily dose used in the Silexan trials. It is the UK product most people mean when they talk about Silexan.
How long does Silexan take to work?
The trials ran for ten weeks, with one 80 mg capsule a day. It is not a quick fix for a stressful afternoon. Give it a few weeks, and stop if you feel no benefit.
Can I take Silexan with antidepressants?
The Kalms leaflet says not to combine it with other medicines for anxiety or that make you sleepy. Ask your pharmacist or prescriber first, and never stop a prescribed medicine to switch.
Should I get a blood test before trying it?
It is worth it if your anxiety is new, constant or comes with a racing heart or weight change. An overactive thyroid and low B12 can both feel like anxiety. If a result is abnormal, see a qualified clinician. This is general information, not medical advice.