Tea and Attention

The tea leaf supplies caffeine and the amino acid L-theanine. Trials of the two together show modest gains in alertness and attention, and caffeine does most of the work [1]. The doses used in those trials are much higher than a cup of tea provides, so how a tea is brewed matters more to what reaches the cup than the reputation of the leaf.

This guide covers what a cup of tea contains, what the trials show, the research on tea ritual, and what is known about safety. Bracketed numbers point to the References at the end.

Caffeine and L-Theanine in the Cup

A 237 mL cup of brewed black tea averages about 48 mg of caffeine and green tea about 29 mg, compared with about 96 mg for brewed coffee [2]. Actual amounts vary widely with leaf, dose, and steep time.

A 2025 study brewed 2 g of leaf in 200 mL and measured what came out. Caffeine ranged from about 4 to 53 mg per infusion depending on tea type and brewing. L-theanine was about 12 to 23 mg in green and black teas and only about 2 to 9 mg in white, yellow, oolong, and pu'er samples [3]. Steeping 5 minutes instead of 2 raised both, and hotter water raised caffeine noticeably only in oolong [3].

L-theanine is the amino acid behind tea's savory taste. It makes up 1 to 2% of dry leaf and is made in the roots and carried up to the shoots, so buds and first leaves hold the most [4]. Shaded teas such as gyokuro and matcha contain more theanine and also more caffeine [5].

For gongfu brewing, the first one or two infusions release the most caffeine, and later infusions release steadily less [6][7].

What the Trials Show

L-theanine has been studied alone and with caffeine:

Theanine alone. In a small 2008 EEG study, 50 mg of L-theanine increased alpha-1 brain activity more than water in people resting with eyes closed. The authors described this as a relaxed but alert state [8]. In another trial, a large 250 mg dose alone slightly worsened some measures and raised headache ratings [9].
Theanine with caffeine. Combinations improved attention switching, alertness, and reaction times in several placebo-controlled crossover trials, using doses of 40 to 150 mg caffeine and 97 to 250 mg L-theanine [9][10][11].
Pooled evidence. A 2014 meta-analysis of 11 placebo-controlled studies found moderate benefits for alertness and attention-switching accuracy within two hours of taking the two together. Caffeine dose appeared to matter more than theanine dose [1].
Stress and sleep. Reviews of supplements at 200 to 400 mg a day suggest small benefits for stress, anxiety, and subjective sleep quality. Their authors say larger and longer trials are still needed [12][13].

The trial doses are much higher than a cup provides. Most studies used 50 to 250 mg of theanine, while a 200 mL infusion holds roughly 2 to 23 mg [3][11]. The tea effect people notice is probably mostly caffeine, with a smaller contribution from theanine [1].

One trial tested real tea over time. In 2007, 75 healthy men drank black tea or a caffeinated placebo for six weeks. The tea group had lower cortisol after a stressful task and reported feeling more relaxed during recovery; blood pressure and heart rate responses did not differ [14].

Ritual and Mindful Drinking

Research on tea ritual itself is thin. In a 2024 randomized trial of 100 adults over eight weeks, guided meditation while preparing and drinking matcha lowered perceived stress by about as much as breathing meditation. The tea group reported slightly greater gains in feeling relaxed and calm [15]. The study was unblinded and was funded by a company that sells the product [15]. A small uncontrolled program in Japan found that participants felt more positive and focused after mindfulness tea ceremony sessions [16].

These results suggest that tea practice works at least as well as other forms of meditation for people who enjoy it. They do not show that tea adds a separate effect.

Brewing for More or Less Caffeine

Since most of the effect comes from caffeine, the brew is the main control. Longer steeps and more leaf raise caffeine, and so do the first infusions of a gongfu session [3][6]. Shorter steeps and later gongfu infusions lower it. Hojicha is roasted and low in caffeine [17]. Gyokuro and matcha are the richest source of theanine, though they also carry more caffeine [5].

Safety

Caffeine. The FDA says up to 400 mg a day is generally not linked to harmful effects in most healthy adults, though sensitivity varies. People who are pregnant or breastfeeding should check with a provider [18].
Iron. Black tea with a meal cut absorption of non-heme (plant) iron by 79 to 94% in one study [19]. People with low iron may want to drink tea between meals.

Timing Your Tea With Tea Timer

Tea Timer keeps steep times exact, for a single cup or a full gongfu session, so the strength of the cup stays consistent from one day to the next. One-tap ratings adjust the timing of later sessions to taste.

Time your next cup