Eight RCTs (909 patients), 21 comparative cohort studies (1,592 patients) and 157 uncontrolled studies (number of patients unclear) were included in the review. The quality of the RCTs was fair, but none of the trials blinded outcome assessors. The quality of the observational studies was limited. Follow-up duration ranged from one month to approximately 15 years, where reported.
Cabergoline was statistically significantly more effective in reducing the risk of persistent hyperprolactinaemia compared to bromocriptine (RR 2.88, 95% CI 2.20 to 3.74; two RCTs, three controlled cohort studies), amenorrhoea/oligomenorrhoea (RR 1.85, 95% CI 1.40 to 2.36; three RCTs, one controlled study) and galactorrhoea (RR 3.41, 95% CI 1.90 to 5.84; one RCT, two controlled studies). Where assessed, there was no evidence of statistical heterogeneity. There were no other significant differences between the two drugs.
There were no statistically significant differences between bromocriptine versus quinagolide (four RCTs, two controlled studies) on any outcome.
Compared to no treatment, dopamine agonists statistically significantly reduced prolactin levels (WMD -44.06, 95% CI -76.81 to -11.31, two controlled cohort studies) and risk of persistent hyperprolactinaemia (RR 0.90, 95% CI 0.81 to 0.99, two controlled cohorts). No other outcomes were statistically significant.
Dopamine agonists were more effective in reducing risk of persistent hyperprolactinaemia compared to surgery alone (three controlled cohorts), but no other outcomes were statistically different. There were no statistically significant differences in any outcomes between surgery versus surgery plus dopamine agonists, dopamine agonists versus surgery plus dopamine agonists.
Subgroup analyses showed no significant interactions based on sex or tumour size.
Uncontrolled cohort studies indicated consistent benefit with bromocriptine (39 studies), cabergoline (26 studies), quinagolide (15 studies) and other dopamine agonists. Prolactin levels were reduced with radiotherapy (eight uncontrolled studies), transsphenoidal surgery (27 uncontrolled studies) and surgery plus dopamine agonists (five uncontrolled studies). Other results were fully reported in the review.
The most frequently reported side effects were nausea, vomiting, headache and hypotension.