How Safe Are Caffeine and L-Theanine?

A brief review of the available scientific literature on caffeine + L-theanine reveals they improve cognitive function together more effectively than either of them do alone. However, these studies were designed to look specifically at the cognitive effects of caffeine + L-theanine. Because the intention of a supplement such as Green Tea Focus is to cause a fast onset mental improvement for a short time, many of these studies focused only on the short-term effects of caffeine + L-theanine. This then begs the question: does taking caffeine + L-theanine to improve mental function have unknown long-term side effects?

The caffeine in the caffeine + L- theanine supplement is familiar to most people, since it is consumed in some form almost daily. L-theanine, on the other hand, is more likely to be viewed with suspicion due to its relative obscurity. The nature of a study examining L-theanine toxicity, however, precludes it from being conducted on humans. For hopefully obvious reasons, you can’t take a substance you’re worried is toxic and give it to a bunch of people to figure out whether it actually is dangerous or not. The same cannot be said however, of rats, which are used as experimental models of humans quite often. In a toxicity experiment conducted in 2006, rats were fed with food containing different concentrations of L-theanine for 13 weeks. The rats weighed around 200 g (avg. male = 226 g, avg. female = 172 g). Even at the highest dose of 4000 mg/kg of bodyweight per day, no adverse effects were seen whatsoever. That concentration translates to 800 g of L- theanine, 4x the dose in a Green Tea Focus pill. Clearly L- theanine is very safe, especially within the dosages used for mental improvement.

While caffeine may be a familiar substance to most people, it is worth wondering exactly how much is used in caffeine + L-theanine. The amount of caffeine in a Green Tea Focus pill is 100 mg, less than the 135 mg of caffeine in a brewed cup of coffee. A 2001 study on caffeine toxicity found that up to 400 mg of caffeine per day for the general population and up to 300 mg per day for reproductive-aged women has no adverse effects. “But how safe are caffeine and L-theanine together?”, you may ask. Well L-theanine actually blocks some of the stimulant effects of caffeine (e.g. jitteriness). In fact, in a 2012 paper, L- theanine was shown to help prevent sleep-disturbance caused by caffeine.

In conclusion, it’s quite clear that L-theanine + caffeine has no long-term side effects, either individually or together. L- theanine was shown to have no adverse effects on the rats it was fed to over 13 weeks at any of the dosages, and there is less caffeine in a Green Tea Focus pill than there is in your morning cup of coffee. L- theanine and caffeine together are, if anything, even safer due to L-theanine’s tempering effect on caffeine.