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Head-to-head evidence comparison — which supplement is right for you?
Vitamin B12 wins 1 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Likely helps
3 of 4 studies with measurable effects showed benefit.
Top outcomes
Verdict
Likely helps
12 of 17 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (1)
Outcomes where both L-Theanine and Vitamin B12 have evidence — compare verdict strength side-by-side.
100-200mg
Morning with coffee for focus, Evening for relaxation, As needed for stress
Suntheanine® capsules or powder
500-1000mcg daily for maintenance; higher for deficiency
Morning (may be energizing), With or without food
Methylcobalamin (sublingual)
30-60 minutes
30-60 minutes
30-60 minutes
Varies
2-4 weeks
4-8 weeks
Weeks to months
The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis
Sleep medicine reviews (2025) · Meta analysis · n=897
The findings indicate the potential use of L-theanine in the management of sleep disturbances; however, the lack of studies on "pure" L-theanine warrants further investigation.
Efficiency of Different Supplements in Alleviating Symptoms of ADHD with or Without the Use of Stimulants: A Systematic Review
Nutrients (2025) · Systematic review
The evidence revealed the potential use of supplements as complementary ADHD treatments under clinical guidance.
Analysis of the Effects of Known Sleep-Support Supplements in Relation to Life Habits, Sleep Conditions, and Sleep Problems
Nutrients (2023) · Rct · n=160
All the tested supplements were found to ameliorate sleep problems significantly (Analysis 1).
Efficacy of different routes of vitamin B12 supplementation for the treatment of patients with vitamin B12 deficiency: A systematic review and network meta-analysis
Irish journal of medical science (2024) · Meta analysis · n=4275
Regarding the hemoglobin level, the pooled effect sizes showed no difference between all routes of administration that could reach statistical significance.
Dosage exploration of combined B-vitamin supplementation in stroke prevention: a meta-analysis and systematic review
The American journal of clinical nutrition (2024) · Meta analysis · n=76664
In areas without and with partial folic acid fortification, combined B-vitamin supplementation significantly reduced the risk of stroke by 34% [RR: 0.66; 95% confidence interval (CI): 0.50, 0.86] and 11% (RR: 0.89; 95% CI: 0.79, 1.00), respectively.
Vitamin Status in Patients with Phenylketonuria: A Systematic Review and Meta-Analysis
International journal of molecular sciences (2024) · Meta analysis · n=770
The effect sizes were expressed as standardised mean differences.
Meta-analysis (n=897) and multiple RCTs support sleep benefits. Studies often used L-theanine in combination with other compounds, limiting pure L-theanine effect attribution. Effects include reduced sleep onset latency and improved subjective sleep quality.
AI-estimated from published studies. Interpret as directional guidance.
Vitamin B12 has a higher evidence score (9/10 vs 9/10) and wins in 1 of 3 categories.
For sharpen focus, L-Theanine has a higher relevance score (80 vs 70).
No known interactions between L-Theanine and Vitamin B12 have been documented in our database. However, always consult a healthcare provider before combining supplements.