L-theanine Side Effects: What Reddit Users Report
28 of 330 Reddit owner comments about L-theanine (8%) describe an unwanted effect. The effects people mention most are headaches. These are self-reports from Reddit anxiety, stress and supplement communities (May 2026 to October 2026), not a measured side-effect rate, and many people report no problems at all.
L-theanine overall: 4.0 · tolerability 4.4 (higher means fewer unwanted-effect reports).
What people describe
| Effect mentioned | Owner comments |
|---|---|
| Headaches | 6 |
How we counted: among the 28 comments that describe an unwanted effect, a category counts when a sentence names the effect with wording like "gave me" or "made me". Questions and sentences about an effect going away are skipped. One comment can count in more than one row, and keyword counts can include some unrelated mentions, so read the quotes below for context.
Most common complaints
- Side effects: 27 owner comments
- Calming effect: 8 owner comments
- Taste & form: 2 owner comments
Safety notes from NIH and published research
- Studies in the 2020 review mostly used 200 to 400 mg a day.[PubMed]
Stop and talk to a doctor if an effect is severe or does not settle. Ask a pharmacist about interactions with any medicine you take.
In their words
4/5 Side effects“I swear by L-Theanine making my social interaction flow a lot smoother.”
1/5 Side effects“L-Theanine did not help me with sleep or stress, at all.”
2/5 Side effects“I've tried L-Theanine and that didn't work for me, if anything, I'm an outlier who gets paradoxical effects from it like hypnic jerks.”
1/5 Side effects“Caffeine + L-Theanine gives me unbearable headaches with high tension.”
2/5 GrogginessSide effects“L theanine gave me a huge spike of calmness and alertness, it also completely eliminated hangovers if I took it before bed.”
4/5 Calming effectGrogginess“L-Theanine calms my mind alot before sleep and NAC before i drink alc heelps alot with hangovers.”
1/5 MoodSide effects“Old thread, but recently also realized that L-Theanine was significantly lowering my mood.”
3/5 Calming effectGrogginess“In the evenings, around 7pm, I take 200 mg of Nature's Trove L-Theanine.”
Frequently asked
What side effects do people report with L-theanine?
28 of 330 Reddit owner comments about L-theanine (8%) describe an unwanted effect; the ones mentioned most were headaches. These are self-reports, not a measured side-effect rate.
Is L-theanine safe?
Safety depends on your health and medicines. The NIH and other sources listed on this page note specific cautions. Ask a doctor or pharmacist before starting, especially if you take other medicines or are pregnant.
More on L-theanine
Compare side-effect reports: L-theanine vs GABA · L-theanine vs Magnesium glycinate · Glycine vs L-theanine · Taurine vs L-theanine · L-theanine vs Magnesium (form not stated) · Saffron extract (incl. Affron) vs L-theanine · L-theanine vs Chamomile · Lemon balm vs L-theanine · NAC (N-acetylcysteine) vs L-theanine