A semi-colon, not a comma, should go before a conjunctive adverb when it joins two sentences or independent clauses.
I don’t like cake, however, I love biscuits.
I don’t like cake; however, I love biscuits.
If the sentences or clauses that are being joined are not complete nor independent then a comma is used not a semi-colon.
- The picnic, however, will start as planned at 3pm.
