Background/Objectives: Hypertension affects over 1.3 billion people globally, and inadequate therapy is reported in 80% of cases. Patients increasingly turn to complementary therapies, including hawthorn (Crataegus spp.), a traditional remedy for cardiovascular diseases. Hawthorn has long been used in folk medicine to lower blood pressure; however, its efficacy has not been fully established. This meta-analysis aimed to evaluate the antihypertensive effects and safety of hawthorn in randomized, placebo-controlled trials. Methods: A systematic review and meta-analysis were conducted, including six studies with a total of 428 participants. The trials focused on systolic (SBP) and diastolic blood pressure (DBP) changes over treatment periods of 10 weeks to 6 months. Literature searches were conducted in the Embase, PubMed, Cochrane, and Web of Science databases. Studies that met the predefined PICO criteria were included. Data analysis was performed using a random-effects model, and the risk of bias was assessed using the Cochrane Risk of Bias Tool. Results: Hawthorn statistically significantly decreased SBP (MD: −6.65 mmHg; 95% CI [−11.72; 1.59]) and non-significantly reduced DBP (MD: −7.19 mmHg; 95% CI [−15.17; 0.79]) after 2–6 months of treatment. Variations in dosage (250–1200 mg/day) and study protocols contributed to this heterogeneity. Conclusions: The effect of hawthorn on blood pressure is clinically significant. However, larger, well-designed trials are needed to establish optimal dosing, duration, and efficacy with greater reliability.

Background: Green tea (Camellia sinensis) has been consumed for centuries, and its beneficial effects on human health have been studied in recent decades. l-theanine, an active ingredient in green tea, has been used to improve cognition and mood. Although the effects of l-theanine on cognition have been investigated in clinical trials that have reported various results, these studies have not yet been critically evaluated in meta-analyses. Objectives: Our objective was to systematically evaluate the efficacy of l-theanine on cognitive functions compared to a placebo, in a meta-analysis based on randomized controlled trials (RCTs). Methods: PubMed, the Cochrane Central Register of Controlled Trials, Embase and Web of Science were searched for relevant studies until 31 July 2024 and registered in PROSPERO (registration number: CRD42024575122). Placebo-controlled clinical trials investigating the efficacy of l-theanine in healthy adults were included. Conference abstracts, study protocols and reports of non-RCTs were excluded. For risk of bias assessment, the Cochrane Risk of Bias Tool (version 2.0) was used. A random effects model was applied to conduct the meta-analysis. Mean differences (MD) with 95% confidence intervals (CIs) were calculated. Results: Based on the included five RCTs involving 148 healthy adults, l-theanine had a dose-dependent effect on cognitive function based on rapid visual information processing and recognition visual reaction time (MD: −15.20 ms; 95%-CI [−28.99; −1.41]). The effects of l-theanine were non-significant on reaction time to a simple stimulus (MD: −0.46 ms; 95% [CI: −15.65; 14.73]) and in the Stroop test (MD: −37.38 ms; 95%-CI [−86.39; 11.62]). Conclusions: The beneficial effects of l-theanine on cognitive performance could not be confirmed by all test methods. The contradictory results could be explained by the fact that l-theanine only affects certain cognitive domains, but also by the low number of trials and the heterogeneity of the test preparations. Further trials using standardized products with larger sample sizes are required for the accurate assessment of efficacy.