Trade between Ireland and Britain "declined sharply" following Brexit, according to a report from the Economic and Social Research Institute (ESRI).
The Initial impact of Brexit on Ireland-UK trade flows paper looks at trade patterns between Britain and Ireland and also for Northern Ireland before and after January 2021.
The ESRI isolated the contribution of Brexit to trade in the first eight months of this year from other factors, including the Covid-19 pandemic.
Researchers found that although Brexit did not cause a significant reduction in overall Irish exports to the UK, there have been sharp declines in food, beverage, fuel and animal fat exports to Britain.
The ESRI said the declines were partially offset by increased exports to Northern Ireland and the phased implementation of customs checks by the UK.
"This suggests that it may take further time for the full effects of Brexit to materialise," the paper said.
The report shows that the overall amount of Irish goods exported to Britain was almost 11% in 2015, but that fell to 6.3% this year.
Produce from Ireland being sent to Northern Ireland increased marginally over that period from 1.4% to 1.7%.
In 2015, Irish food exports to Britain stood at 27%; this year, that had declined to 18.6%.
There was a sharp fall in beverages sent to Britain from 17.6% to 7.2%; the export of fuel and animal fat to the UK also dramatically fell.
The amount of goods imported from Britain to Ireland fell from 23.2%in 2015 to 7.2% this year.
British food produce brought into Ireland fell from 29% in 2015 to almost 12% this year; beverages tumbled from 31% to 9.3%.
The amount of fuel imported to Ireland from Britain dropped from nearly 37% in 2015 to 11% this year; the ESRI said this can be explained by travel restrictions during the Covid-19 pandemic.
Machinery imports from Britain dropped from 15.2% to 5.3% over the timeframe.
Goods imported from Northern Ireland to Ireland increased from 1.5% in 2015 to 5% in the wake of Brexit.
The ESRI noted that the increase was from a low base and does not offset the decline in trade with Britain.
However, the think tank said that the boost in trade with Northern Ireland is significant and can be attributed to changes in supply chains, including companies redirecting trade routes.
The ESRI said that more information is needed to quantify how the increase in trade between Ireland and Northern Ireland is as a result of substitution away from trade with the UK by firms in the North.
The ESRI also noted that the impact of the Northern Ireland Protocol on trade is a potential avenue of research.