Why Does L-Theanine Calm One Child and Make Another Much Worse?
L-theanine is meant to be calming.
That is probably why you tried it.
Maybe your child was anxious. Maybe they couldn't switch off at night. Maybe someone told you it was good for cortisol, stress or sleep.
And sometimes it is brilliant.
I've seen children noticeably soften on it. They are calmer without being sleepy. Bedtime gets easier. The constant sense that their nervous system is running at full speed finally comes down a notch.
But I've also seen the complete opposite.
A child becomes more anxious.
Another becomes irritable.
Someone else suddenly can't sleep.
A parent notices the OCD is worse.
Or the tics increase.
Not necessarily all of those things at once. Usually it is one or two.
And understandably, parents are baffled.
How can something that is supposed to calm the brain make a child more wired?
The answer is that L-theanine is doing considerably more in the brain than the label on the bottle would have you believe.
L-theanine isn't just a "calming amino acid"
One of the problems with supplements is that they get reduced to one-line explanations.
Magnesium = calming.
L-theanine = lowers cortisol.
Melatonin = sleep.
Biology isn't that tidy.
L-theanine crosses into the brain and interacts with several of the systems involved in how we regulate anxiety, attention, movement, sleep and inhibition.
That includes GABA, glutamate and dopamine.
And that is where things start to get interesting.
Because the effect of changing those systems depends on what they were doing before you gave the supplement.
“A supplement can be calming in one nervous system and activating in another. The question is not what L-theanine is supposed to do. It’s what it does in your child.”
Two children can look anxious for completely different reasons
This is the bit I think matters most.
Imagine two children who both look wired and anxious.
The first child is tense. Vigilant. They can't switch off. Their body seems permanently braced for something to happen. At night they are tired but still can't settle.
That is the child in whom L-theanine can sometimes work beautifully.
Now imagine another child who is also anxious, but the picture is different.
Their symptoms fluctuate.
They may have tics.
OCD suddenly gets much worse.
Behaviour changes abruptly.
Sleep falls apart during infections.
They can go from relatively settled to completely dysregulated within days.
On the surface, both children have "anxiety".
Underneath, they may have very different nervous systems.
And I suspect that distinction explains quite a lot of the very different reactions we see.
It may be better for an over-alert brain than an unstable one
This is the way I currently think about it clinically.
There is a difference between a nervous system that is too switched on and one that is struggling to regulate its signals properly.
L-theanine seems particularly well suited to the first group.
The child who is:
physically tense
vigilant
stress-driven
unable to switch off
restless at bedtime
anxious but otherwise fairly stable
may do extremely well.
But I am much more cautious when I see:
active tics
rapidly changing OCD
a significant PANS/PANDAS flare
sudden behavioural volatility
worsening symptoms during infection
a history of reacting badly to supposedly calming supplements
That doesn't mean every child with PANS, PANDAS or autism should avoid L-theanine.
Absolutely not.
I've seen it work very well in some of these children.
The point is that the diagnosis doesn't tell me enough.
The child's current neurological state probably matters much more.
Why do tics and OCD make me pay attention?
Because the parts of the brain involved in tics and OCD are heavily dependent on some of the same signalling systems that L-theanine can influence.
Dopamine is particularly important in the basal ganglia, the deep brain structures involved in movement, habits, inhibition and repetitive behaviour.
Glutamate and GABA are involved too.
In a reasonably stable system, gently altering those signals may be helpful.
In a system that is already struggling to regulate them, the result may be unpredictable.
That doesn't mean L-theanine is damaging the brain.
It may simply mean that this is the wrong nervous system, or the wrong moment, for that particular nudge.
And that distinction matters.
What about autism?
Autism alone would never make me automatically avoid L-theanine.
Autism is far too heterogeneous for that.
Two autistic children can have completely different biology underneath what looks like a similar diagnosis.
One may be predominantly anxious and hyperaroused and respond wonderfully.
Another may have significant sensory volatility, tics, OCD, sleep disruption and a history of paradoxical reactions.
Those are very different children clinically.
This is why I dislike supplement lists that say:
"Best supplements for autism."
There is no such list.
The question is always: what is happening in this child?
And what about PANS and PANDAS?
This is where I become even more interested in timing.
A child with PANS may tolerate something perfectly well when stable and react completely differently during a flare.
Parents tell us this all the time with supplements.
"She used to take it with no problem."
"He had this for months and suddenly can't tolerate it."
That isn't necessarily inconsistent.
The nervous system they are giving it to today may not be in the same state it was six months ago.
If OCD has suddenly escalated, tics have returned, sleep has deteriorated and the child is clearly in an inflammatory flare, I am generally much less interested in introducing something that changes several neurotransmitter systems at once.
First stabilise the child.
Then reassess what you actually need.
Is it the COMT gene?
This comes up a lot.
COMT helps break down catecholamines including dopamine, so it is tempting to blame a "slow COMT" gene whenever a child reacts badly to something affecting neurotransmitters.
I don't think we have enough evidence to do that with L-theanine.
COMT could certainly be one small piece of an individual child's response.
But I would not look at a COMT result and decide from that whether a child should or shouldn't take L-theanine.
The child's actual response and phenotype tell me considerably more.
So who do I think L-theanine suits best?
The child I am most interested in using it with is the child who looks over-alert rather than neurologically unstable.
Tense.
Anxious.
Can't switch off.
Perhaps struggling to settle at bedtime.
But otherwise relatively stable.
That is where it can be a genuinely lovely supplement.
The child I am much more cautious with is the one whose picture is currently dominated by tics, abrupt OCD, significant behavioural volatility or an active PANS/PANDAS flare.
Not because L-theanine is "bad" for those children.
Because when those circuits are already unstable, the response seems far less predictable.
And if your child reacts?
Believe what you are seeing.
If you introduce L-theanine and your child becomes noticeably more anxious, irritable, wakeful, compulsive or ticcy, don't keep increasing it because someone told you it is supposed to be calming.
The response matters more than the theory.
That reaction may also be telling you something useful about the kind of nervous system you are dealing with.
And that is often far more valuable than finding another supplement to push through the symptom.
The question isn't really whether L-theanine is a good supplement.
It is.
The better question is:
Is it a good supplement for this child, in this neurological state, right now?
IMPORTANT
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. Always consult with medical doctors or qualified functional medicine practitioners before introducing any new supplement, test, or intervention.
If this has raised questions about your child, we'd love to help you find some answers.
REFERENCES
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Lyon MR, Kapoor MP, Juneja LR. The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Alternative Medicine Review. 2011;16(4):348-354. PMID: 22214254. PubMed
Scheid L, Ellinger S, Alteheld B, et al. Kinetics of L-theanine uptake and metabolism in healthy participants are comparable after ingestion of L-theanine via capsules and green tea. Journal of Nutrition. 2012;142(12):2091-2096. doi:10.3945/jn.112.166371. PMID: 23096008. PubMed
Kimura K, Ozeki M, Juneja LR, Ohira H. L-Theanine reduces psychological and physiological stress responses. Biological Psychology. 2007;74(1):39-45. PMID: 16930802.
