We sell a supplement containing ashwagandha and rhodiola, so we have an interest here. We have tried to be straight about what the rules actually allow anyone to claim, including us. General information, not medical advice.
Quick answer: a cortisol blocker supplement is a marketing name rather than a type of medicine, and no supplement sold in the UK is allowed to claim it blocks or lowers cortisol, because no such health claim has been authorised. These products contain some combination of ingredients such as ashwagandha, rhodiola, magnesium, vitamin C and vitamin B6, and only the last three have authorised claims, which are about psychological function and tiredness, not cortisol. Genuine cortisol-blocking drugs are prescription medicines for conditions such as Cushing's syndrome.
Do supplements to reduce cortisol actually work?
No supplement has an authorised claim that it reduces cortisol. There is no authorised health claim for lowering, reducing or blocking cortisol on the GB Nutrition and Health Claims Register.
That is not a technicality. It means that every product marketed to you as a cortisol supplement, cortisol blocker or cortisol tablet is either making a claim it is not allowed to make, or is carefully not making it while letting the product name imply it.
What is true is more modest. Some ingredients commonly found in these products do have authorised claims, though not about cortisol. Others have a research base that is real but unsettled. And a few have very little behind them at all.
This page goes through which is which, so you can read a label properly.
What the ingredients actually have behind them
This is the table we think every brand selling these products should publish. An authorised claim means the ingredient has been assessed and approved for a specific wording in the UK. Everything else is either traditional use or unsettled research.
| Ingredient | Authorised UK claim? | What it can honestly be described as |
|---|---|---|
| Magnesium | Yes | Contributes to normal psychological function and to the reduction of tiredness and fatigue |
| Vitamin C | Yes | Contributes to normal psychological function, normal nervous system function, and reduction of tiredness and fatigue |
| Vitamin B6 | Yes | Contributes to normal psychological function and to the reduction of tiredness and fatigue |
| Ashwagandha | No. On the EFSA on-hold list | A botanical with a long history of traditional use |
| Rhodiola rosea | No. On the EFSA on-hold list | A botanical with a long history of traditional use |
| L-theanine | No | Studied, but no approved wording |
| Phosphatidylserine | No | Studied, but no approved wording |
| Omega-3 | Partial | EPA and DHA have claims for heart, brain and vision, not for stress |
Notice what is missing from every row. Not one of them has an authorised claim about cortisol, because none exists.
The most useful thing on that table is the top three. Magnesium, vitamin C and vitamin B6 are the ingredients with actual approved wording behind them, they are cheap, and they are the least glamorous things in most cortisol formulas.
What about ashwagandha and rhodiola?
Ashwagandha and rhodiola are the two you will see most, and they are the reason most of these products exist.
Both are botanicals with a long history of traditional use. There is published research on both, some of it looking at cortisol, which is why the claim gets made so confidently.
But research existing is not the same as a claim being authorised. Botanical claims in the UK sit on the EFSA Article 13.1 on-hold list: submitted, not yet approved. That is why a brand describing ashwagandha by its traditional use is being accurate, and a brand telling you it lowers your cortisol is not.
If you are comparing products, check the dose. The ashwagandha research is mostly on standardised extracts at around 600mg a day, and a lot of products contain considerably less than that without saying so. We go through how to read a label in our guide to KSM-66 ashwagandha, and the same principle applies to buying rhodiola in the UK.
Cortisol blockers and cortisol tablets: what are they?
A cortisol blocker is a marketing category, not a pharmacological one. Products sold under that name are supplements containing some combination of the ingredients above. They do not block anything in the sense the name implies.
Genuine cortisol-blocking drugs exist and are prescription medicines used to treat specific conditions such as Cushing's syndrome. They are not sold as supplements and you would not want to take one without a diagnosis.
Cortisol tablets is the same thing in a different wrapper. The word tablet describes the format, not what is in it. Read the ingredient panel rather than the product name.
What to check on any of them:
- Is every dose published? A proprietary blend listing ten ingredients with one combined weight is hiding the amounts, and the reason is usually that they are small
- Is the extract standardised? Generic root powder at 600mg is not the same as a standardised extract at 600mg
- What does the label actually claim? If it says it lowers cortisol, it is over-claiming, and that tells you something about the rest of the product
What the evidence supports
Unglamorous, free, and better evidenced than anything on a shelf.
Sleep. Cortisol follows a daily rhythm tied closely to your sleep-wake cycle. Poor or short sleep affects it, and no supplement is a substitute for fixing it.
Caffeine timing. Caffeine raises cortisol. Cutting back after midday helps a surprising number of people and costs nothing to try.
Movement, but not to exhaustion. Moderate exercise helps. Hard training when already depleted tends to work against you.
Alcohol. It disrupts sleep architecture even when it helps you fall asleep, which is the mechanism that matters here.
And checking whether something else is going on. Thyroid function, iron levels and vitamin D deficiency all produce the same tired, flat, unfocused feeling, and all are things a GP can check with a straightforward blood test.
Should you get your cortisol tested first?
A fair question, and the honest answer is usually no.
Cortisol follows a daily rhythm, highest in the morning and lowest late at night, and it rises in response to ordinary things like a stressful commute or a bad night's sleep. A single reading, taken at the wrong time and interpreted without clinical context, tells you very little.
If you have symptoms that worry you, speak to your GP. The standard test is a 9am serum cortisol, timed for when levels are naturally at their peak, and it comes with someone qualified to interpret it. That is free and it is more useful than a postal kit.
Be careful with at-home saliva and urine kits. The method has genuine clinical uses, but what you usually get is a number, a chart and no clinician. You will also see adrenal fatigue used to sell them, which is not a recognised medical diagnosis whatever the marketing says. Adrenal insufficiency is real, serious, and diagnosed by a doctor.
Where we fit
We make the Flissie Perimenopause Supplement, a daily formula containing KSM-66 Ashwagandha, with Rhodiola, Chamomile, Chaste Tree, Maca, Wild Yam, Fennel, Broccoli Sprout Extract, Rosemary, Gymnema and Vitamin B6. Every dose is published on the product page.
It is not a cortisol supplement, and we do not sell it as one.
What we can honestly say: Vitamin B6 contributes to normal psychological function and to the reduction of tiredness and fatigue, both authorised claims. None of the ten botanicals, ashwagandha included, has an authorised health claim, so we make none.
And no supplement is a substitute for finding out what is wrong. If you have symptoms that concern you, see your GP first, and check with them before taking any supplement.
Not suitable in pregnancy or while breastfeeding, or with hormonal contraception, because it contains chaste tree. Avoid it if you have, have had or are at increased risk of a hormone-sensitive condition, because it contains wild yam. If you take thyroid medication, speak to your GP first.
See the formula and every published dose.
Questions
Do supplements to reduce cortisol work?
No supplement sold in the UK is permitted to claim it reduces cortisol, because no authorised health claim exists for that. Some ingredients commonly included, such as magnesium, vitamin C and vitamin B6, do have authorised claims for psychological function and tiredness. Ashwagandha and rhodiola have no authorised health claim at all.
What is the best supplement to reduce cortisol?
The honest answer is that no product can be sold to you on that basis. If you are choosing between formulas, judge them on whether every dose is published, whether extracts are standardised, and whether the ingredients with authorised claims are present at meaningful amounts rather than as a token.
What supplements lower cortisol?
None are authorised to say they do. Ashwagandha and rhodiola are the ingredients most often included, and neither has an authorised health claim. Magnesium, vitamin C and B6 are the ones with approved claims, though those claims are about tiredness and psychological function rather than cortisol.
Are cortisol blockers real?
Cortisol blocker is a marketing name, not a pharmacological category. Products sold under it are supplements. Genuine cortisol-blocking drugs are prescription medicines used for specific conditions such as Cushing's syndrome, and are not sold over the counter.
What are cortisol tablets?
A format rather than an ingredient. Cortisol tablets are supplements containing some combination of vitamins, minerals and botanicals such as ashwagandha and rhodiola. Read the ingredient panel and the doses rather than the product name.
How can I reduce cortisol without supplements?
Sleep is the biggest lever, followed by caffeine timing, moderate rather than punishing exercise, and reducing alcohol. All are free, and none depends on a supplement.
Should I get my cortisol tested?
Usually not. Cortisol swings through the day, so a single reading tells you little without clinical context. If you have symptoms that worry you, ask your GP, who can arrange a properly timed test and look at thyroid, iron and vitamin D at the same time.
How long do ashwagandha and rhodiola take to work?
Neither ashwagandha nor rhodiola has an authorised health claim in the UK, so no one can honestly promise you a result, or a time by which you will notice one.
Does magnesium lower cortisol?
No authorised claim says it does. Magnesium's authorised claims include normal psychological function and the reduction of tiredness and fatigue, and none is about cortisol. It is one of the cheapest, least glamorous ingredients in most cortisol formulas.
Is adrenal fatigue a real condition?
No. Adrenal fatigue is not a recognised medical diagnosis, whatever the marketing for saliva kits says. Adrenal insufficiency is real and serious, and it is diagnosed by a doctor, so if you are worried, see your GP.
What is a 9am cortisol test?
The standard test for cortisol: a blood test of serum cortisol taken at 9am, when levels are naturally at their peak, arranged and interpreted by a GP. It is free, and more useful than an at-home saliva or urine kit, which usually gives you a number and a chart but no clinician.
