Eight double-blind RCTs were included in the review. Four were crossover trials and one study was unpublished. The number of participants randomised was 340, but there was incomplete reporting of how many of these participants were analysed.
The results of the quality assessment showed that two studies scored 2 out of a possible value of 5 on the Jadad scale, three studies scored 3, two studies scored 4 and one study scored 5.
Four trials tested dietary supplements. Statistically significant differences were observed between the overall hangover symptom scores of groups in one trial using gamma-linolenic acid from borago officinalis (borage) and in another using a yeast-based preparation, when compared with placebo. Specific reductions in headache, laziness and tiredness were observed in the former trial (P<0.01). In the yeast-based trial, specific reductions in discomfort, restlessness and impatience were observed (P<0.05). The other two trials (testing cynara scolymus and opuntia ficus-indica) did not report any statistically significant differences between the groups (P>0.05).
The study that evaluated cynara scolymus reported redness in the face in one case of those receiving the intervention.
Four trials tested conventional agents. A statistically significant difference was observed in the overall hangover symptom score between groups given tolfenamic acid in comparison with placebo (P<0.01). Specific reductions in headaches, nausea, vomiting, thirst, dry mouth, tremor and irritation were seen. The remaining trials (employing propranolol, tropisetron, and fructose or glucose) did not report any statistically significant differences between the groups (P>0.05).
The study that evaluated tolfenamic acid reported swollen eyes and slight dysuria in two cases of those receiving the intervention.