The combination of caffeine and L-theanine, particularly at a 1:2 ratio, has garnered significant interest in the field of cognitive enhancement and mood modulation. Research indicates that this specific combination can lead to improved cognitive performance, increased alertness, and reduced anxiety, making it a compelling subject for further exploration.

Studies have shown that the combination of caffeine and L-theanine can enhance cognitive functions such as attention and memory. For instance, a systematic review by Camfield et al. suggests that the intake of L-theanine and caffeine together improves attention switching and intersensory attention in healthy adults (Kahathuduwa et al., 2020). Furthermore, Giesbrecht et al. found that the combination significantly improved cognitive performance and subjective alertness compared to placebo, highlighting the synergistic effects of these compounds (Giesbrecht et al., 2010). This is particularly relevant in contexts requiring sustained attention, as demonstrated in a study involving children with ADHD, where the combination was shown to enhance sustained attention and inhibitory control (Kahathuduwa et al., 2020).

Moreover, the physiological effects of this combination are noteworthy. Dodd et al. reported that L-theanine can mitigate the rise in blood pressure typically induced by caffeine, suggesting a balancing effect that could enhance overall cognitive function without the adverse effects commonly associated with caffeine alone (Dodd et al., 2015). This is supported by findings from Yoto et al., who noted that L-theanine could attenuate blood pressure elevation during mental tasks, further indicating its potential to counteract caffeine's stimulatory effects (Yoto et al., 2012).

The mechanisms underlying these effects may involve the modulation of neurotransmitter systems. L-theanine is known to promote relaxation by increasing GABA levels, which can counteract the excitatory effects of caffeine, a non-selective antagonist of adenosine receptors (Ritsner et al., 2010). This interaction suggests that while caffeine enhances alertness, L-theanine provides a calming effect, leading to a state of relaxed alertness that is beneficial for cognitive tasks (Zameer et al., 2013).

Additionally, the specific ratio of these compounds appears to be crucial. Research indicates that a higher ratio of L-theanine to caffeine, such as 2:1, may optimise cognitive benefits while minimising potential negative effects like anxiety or jitteriness associated with caffeine consumption (Giles et al., 2017). This is consistent with findings that suggest the balance between these two compounds can influence their overall efficacy in enhancing cognitive performance and mood (Unno et al., 2018).