Seven studies were reviewed; three RCTs, three cohort studies and one experimental study. The total number of participants was not reported.
One small placebo-controlled RCT (27 participants) that scored 86% on internal validity found that benztropine had a positive effect on drooling; however, the proportion of drop-outs was 30%. One experimental study that scored 57% on internal validity indicated that benztropine had a positive effect on salivary flow.
One RCT (39 participants) that did not have good internal validity (52%) concluded that a marked improvement in drooling was found with glycopyrrolate. However, treatment had to be withdrawn in 20% of cases because of adverse events.
The authors reported that, on the basis of a poor-quality cohort study scoring 40% on internal validity, no statement could be made about the efficacy of glycopyrrolate. A case series that scored 66% on internal validity also provided insufficient evidence on the effect of glycopyrrolate.
One cohort study that scored 67% on internal validity found that benzhexol hydrochloride had a positive effect on drooling and that the optimal dosage varied from 2 to 3 mg twice daily.
One poor-quality placebo-controlled RCT that scored 57% on internal validity provided evidence on the possible side-effects of a transdermal application of scopolamine.