Can you take magnesium and L-theanine together?
Magnesium and L-theanine have no interaction listed in the NIH magnesium fact sheet, which gives four medicine groups as examples of what magnesium interacts with: bisphosphonates, tetracycline and quinolone antibiotics, diuretics and proton pump inhibitors.[5] For healthy adults, the practical ceiling is the magnesium: 400 mg a day or less from supplements.[1]
Magnesium is a mineral the body cannot make. UK adults aged 19 to 64 need 300 mg a day (men) or 270 mg a day (women), and the NHS lists spinach, nuts and wholemeal bread among its food sources.[1] Only about 30% to 40% of the magnesium in food is typically absorbed.[5]
L-theanine is an amino acid found in tea leaves. It has no nutrient reference value in UK labelling law.[3] The European Food Safety Authority assessed it in 2011 and concluded that a cause-and-effect relationship with the maintenance of normal sleep had not been established.[4] The Great Britain claims register lists every L-theanine claim as non-authorised.[11] Magnesium L-threonate, a form of magnesium, is a different substance despite the similar name.
What does the research on magnesium and L-theanine show?
Research on magnesium and L-theanine has mostly tested each one separately, and both evidence bases are small. A 2021 meta-analysis of three trials in 151 older adults reported that, in the two trials that measured it (55 people), participants fell asleep 17.36 minutes sooner on magnesium than on placebo; the authors rated the evidence low to very low quality.[6]
For L-theanine, which our guide to L-theanine for sleep covers on its own, a 2019 crossover trial gave 30 healthy adults 200 mg a day for four weeks. Three sleep sub-scores of the Pittsburgh Sleep Quality Index — time to fall asleep, sleep disturbance and use of sleep medication — fell compared with placebo. Two of the authors worked for the company that supplied the L-theanine.[7]
The pair itself has barely been tested in people. The most direct study, published in 2022, gave magnesium–L-theanine compounds to rodents in a drug-induced sleep model.[10] Human trials that included both have tested them inside multi-ingredient blends, such as one combining six ingredients,[8] so they cannot show what magnesium and L-theanine contributed on their own.
| Study | Who | What was given | Sleep finding |
|---|---|---|---|
| Mah and Pitre, 2021[6] | 151 older adults, 3 trials (sleep-onset result: 2 trials, 55 adults) | Magnesium vs placebo | Fell asleep 17.36 min sooner; evidence low to very low quality |
| Hidese et al., 2019[7] | 30 healthy adults | L-theanine 200 mg a day, 4 weeks | Sleep-latency, disturbance and medication sub-scores fell |
| Noah et al., 2022[8] | 100 adults who completed it | Magnesium, vitamins B6, B9 and B12, rhodiola and green tea L-theanine, 28 days | Daytime sleepiness score improved by day 56; sleep was an exploratory outcome |
| Dasdelen et al., 2022[10] | Rodents | Magnesium–L-theanine compounds | Shorter sleep latency in a drug-induced sleep model |
Sources: the four studies as cited. The 2022 human trial was sponsored by Sanofi; the 2019 trial's L-theanine was supplied by the employer of two of its authors.
How much magnesium and L-theanine do people take?
The amounts that turn up in research and UK guidance are about 200 mg of L-theanine a day, the dose in the 2019 trial,[7] and no more than 400 mg a day of magnesium from supplements.[1] Count the elemental magnesium, not the weight of the compound: in one trial, 500 mg of magnesium oxide provided 300 mg of magnesium.[5]
| Figure | Amount | Source |
|---|---|---|
| Magnesium UK adults need a day, from food | 300 mg (men), 270 mg (women) | NHS[1] |
| Magnesium from supplements unlikely to cause harm | 400 mg a day or less | NHS[1] |
| Magnesium nutrient reference value (NRV) on UK labels | 375 mg | Regulation 1169/2011, Annex XIII[3] |
| L-theanine in the 2019 trial | 200 mg a day for 4 weeks | Hidese et al.[7] |
| Nutrient reference value for L-theanine | None set | Regulation 1169/2011, Annex XIII[3] |
Sources: NHS, legislation.gov.uk and the trial as cited.
Diarrhoea is the most common side effect of oral magnesium, according to an NHS prescribing guideline.[2] The NIH lists the carbonate, chloride, gluconate and oxide forms as the ones most often reported to cause it.[5] Our guide to magnesium for sleep compares glycinate, citrate and oxide in detail, so this article does not repeat it.
When should you take magnesium and L-theanine?
Magnesium and L-theanine are usually taken in the evening when the aim is sleep, but no trial has compared timings for the pair. The timing rules that do carry numbers are about medicines: keep magnesium at least 2 hours away from bisphosphonates, and take tetracycline or quinolone antibiotics 2 hours before or 4 to 6 hours after it.[5]
Who should not take magnesium and L-theanine?
The NIH Office of Dietary Supplements warns that the risk of magnesium toxicity rises with impaired kidney function, so people with kidney disease should not take magnesium supplements without medical advice.[5] Check with a pharmacist first if you take bisphosphonates, tetracycline or quinolone antibiotics, diuretics, proton pump inhibitors or blood pressure medicines, or if you are pregnant or breastfeeding.
| Situation | Why it matters | Source |
|---|---|---|
| Kidney disease | Excess magnesium is not cleared; an NHS guideline puts people with renal impairment at higher risk of side effects | NIH ODS; NHS Barnsley[5][2] |
| Bisphosphonates, such as alendronate | Magnesium can cut their absorption; keep at least 2 hours apart | NIH ODS[5] |
| Tetracycline or quinolone antibiotics | Magnesium binds them; antibiotic 2 hours before or 4 to 6 hours after | NIH ODS[5] |
| Proton pump inhibitors for more than a year | Can cause low magnesium; in 25% of reviewed cases supplements did not correct it, so testing belongs with your GP | NIH ODS[5] |
| Blood pressure medicines | In a 14-person trial, L-theanine blunted the rise in blood pressure during a mental task in those whose pressure rose most; no study has tested it alongside blood pressure medicines, so a combined effect is theoretical | Yoto et al.[9] |
| Bowel conditions with diarrhoea | Diarrhoea is the most common side effect of oral magnesium | NHS Barnsley[2] |
Sources: NIH Office of Dietary Supplements, NHS Barnsley prescribing guideline and the trial as cited. Ask your pharmacist for the gap that fits your own prescription.
We found no UK guidance covering L-theanine supplements in pregnancy, breastfeeding or childhood, so ask your midwife, GP or pharmacist before using either ingredient in those situations. Low magnesium itself is a blood-test diagnosis: the NHS guideline recommends supplementation below 0.4 mmol/L, against a reference range of 0.7 to 1.0 mmol/L.[2] If you suspect it, that is a conversation for your GP, not a reason to self-dose.
Magnesium and theanine in Vitgem Night-Time
Vitgem Night-Time gummies contain both ingredients: each gummy carries 100 mg of L-theanine and 40 mg of magnesium from magnesium glycinate, alongside ashwagandha, passionflower, lemon balm and chamomile extracts, in a melatonin-free, vegan pectin base. 40 mg is 11% of the 375 mg NRV,[3] and the label maximum is two gummies a day. We make no magnesium claim for it, and L-theanine has no authorised claim at all.[11]
If you already take a magnesium supplement, count each gummy's 40 mg towards the 400 mg a day guide:[1] two gummies add 80 mg. The same rules on kidney disease and medicine spacing apply to a gummy as to a tablet.
- No interaction between magnesium and L-theanine is listed by the NIH; keep supplemental magnesium to 400 mg a day or less.
- The most direct study of magnesium–L-theanine compounds was in rodents; the pair has barely been tested in people.
- A 2021 review reported that older adults fell asleep 17.36 minutes sooner on magnesium in two small trials (55 people), on low-quality evidence.
- Keep magnesium 2 hours from bisphosphonates; take tetracycline or quinolone antibiotics 2 hours before or 4 to 6 hours after it.
- Kidney disease, long-term proton pump inhibitors and blood pressure medicines mean asking a pharmacist or GP first.
If you are comparing formats across our Vitgem gummies, our melatonin-free Night-Time Sleep Gummies print every amount per gummy on the label, with no proprietary blend.
Related reading
- Magnesium for sleep in the UK: best form, dose and timing
- L-theanine for sleep: how it works and dosage
- Natural sleep aids in the UK: an evidence-based guide
References
- NHS. Vitamins and minerals — Others: magnesium. NHS website. link
- Turrell G. Oral magnesium supplementation for hypomagnesaemia. Barnsley Hospital NHS Foundation Trust / NHS Barnsley prescribing guideline, 2016. link
- Regulation (EU) No 1169/2011 on the provision of food information to consumers, Annex XIII (as retained in UK law). legislation.gov.uk. link
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on the substantiation of health claims related to L-theanine from Camellia sinensis (tea) and improvement of cognitive function, alleviation of psychological stress, maintenance of normal sleep and reduction of menstrual discomfort. EFSA Journal 2011;9(6):2238. link
- NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals. Updated 6 January 2026. link
- Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complement Med Ther 2021;21:125. link
- Hidese S, Ogawa S, Ota M, et al. Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial. Nutrients 2019;11(10):2362. link
- Noah L, Morel V, Bertin C, et al. Effect of a combination of magnesium, B vitamins, rhodiola, and green tea (L-theanine) on chronically stressed healthy individuals — a randomized, placebo-controlled study. Nutrients 2022;14(9):1863. link
- Yoto A, Motoki M, Murao S, Yokogoshi H. Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses. J Physiol Anthropol 2012;31:28. link
- Dasdelen MF, Er S, Kaplan B, et al. A novel theanine complex, Mg-L-theanine improves sleep quality via regulating brain electrochemical activity. Front Nutr 2022;9:874254. link
- Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. GOV.UK, updated 19 May 2026. link