They used it at a very high dosage (just my opinion). That dosage in human terms goes from 3 to 5 grams, depending on your weight, per day.

It's a very useful supplement for a wide variety of issues though so it may well be worth a try, but I'm sure I won't be mega dosing it, like the study did.

Here;s a good link on it ..
http://examine.com/supplements/Berberine

Quote ..
Acute administration of Berberine at 5mg/kg injections can raise neural dopamine by 31% in mice, which increased to 53% over 15 days of administration; no further increase was noted at 10mg/kg injections over 15 days though (31%).[82] Ingestion of 20mg/kg Berberine in mice failed to significantly modify dopamine in the striatum, frontal cortex, or hippocampus.[83]