Does L-theanine cut the side effects of caffeine?

Short answer

Mostly no. The only trial where it blocked caffeine's blood pressure rise used 200 mg of theanine; at the amount in 1-2 cups of tea, blood pressure still went up. Jitters and anxiety did not drop either.

Does L-theanine cut the side effects of caffeine?
'Caffeine + theanine = all the alertness, none of the side effects' — true?
L-theanine is an amino acid found in green tea. It often goes into pre-workout supplements with the claim that it cuts caffeine's side effects like jitters, anxiety and a rise in blood pressure. We checked each side effect one by one.
Blood pressure: one trial blocked it
When 200 mg of theanine was added to 250 mg of caffeine
48 people took 250 mg of caffeine, 200 mg of theanine, both, or a placebo. Caffeine raised blood pressure, jitters and alertness. Taken together with theanine, caffeine's rise in blood pressure disappeared.
But at the amount in 1-2 cups of tea, it was different
Blood pressure still rose with both together
When 24 people took 75 mg of caffeine with 50 mg of theanine, the amount in 1-2 cups of tea, systolic blood pressure was higher than with a placebo. What's more, the focus and mood boost from caffeine disappeared. Only the high-theanine trial blocked the blood pressure rise.
Jitters: no reduction
Not even in the trial that blocked blood pressure
In the same trial of 48 people where 200 mg of theanine blocked the blood pressure rise, theanine did not change the jitters caused by caffeine. Alertness and other mood scores did not differ either.
Anxiety: theanine alone made no difference
Pooled results from 31 trials and 1,168 people
A 2026 analysis that pooled 31 trials and 1,168 people found that theanine did not lower anxiety scores compared with a placebo. The drop in stress after a single dose was small, and even that was driven by low-quality studies.
Sleep: theanine helped a little, but not with caffeine
No sleep trial tested it alongside caffeine
An analysis that pooled 18 trials and 897 people found that theanine slightly shortened the time to fall asleep and improved self-rated sleep quality. But no study in people tested whether theanine restores sleep lost to caffeine.
Bottom line: theanine was not a fix for caffeine's side effects
The formula breaks at 'none of the side effects'
Only one trial, using 200 mg of theanine, blocked caffeine's blood pressure rise; at tea-level amounts blood pressure still rose. Jitters and anxiety did not drop, and no study in people showed it protects sleep from caffeine. The side effects came down to the caffeine dose, not theanine.