Twenty-four studies (2,619 participants; range 13 to 500) were included. There were 21 randomised controlled trials (RCTs) and three uncontrolled studies. Twenty studies were described as being double blind.
Passion flower: One small RCT (36 participants) found no difference between passion flower and oxazepam for chronic anxiety symptoms. Significant effects on anxiety, favouring passion flower, compared with placebo, were reported in two RCTs (one for passion flower alone and one in a combination). Mild adverse events were reported in one trial.
Kava: Six RCTs and one observational study indicated significant benefit from kava for anxiety, but four RCTs showed no benefit from kava either alone or with St John's wort. From the 435 patients taking kava, there were no reports of liver toxicity; mild-to-moderate adverse events were reported.
St John's wort: Three RCTs indicated no difference in effect, compared with placebo, but one RCT found a significant reduction in anxiety with St John's wort. The results of two observational studies were reported. All side-effects were mild to moderate.
Lysine: The results of studies in healthy volunteers indicated that lysine could reduce anxiety (one RCT) and the ability to handle induced stress through an increase in cortisol (one RCT). There were no reported adverse effects.
Magnesium: Three placebo-controlled RCTs indicated that magnesium could reduce anxiety, when taken as part of a combination, but there was no evidence that the effects were solely due to magnesium. One of these trials, of women with premenstrual anxiety, also found that magnesium alone was no more effective than placebo. There were very few reported side-effects.