Unfortunately, I do not have a decent series of pictures of contemporary Roman medallions with which to compare, therefore I am left guessing.
I am compelled to ask the same question that echizento has posed:
'Can you say where it come from?'
Verified provenance in this case would be critical.
I would ASSUME that most genuine Roman medallions would have been struck, but my reasoning must leave the door open to allow for casting with large pieces of say, 40 grammes or more. Much effort would have been needed, even with the flan hot, to strike medallions of say, 40 grammes or more. This leads me to reasoning that the largest contemporary Roman medallions could have been cast.
Having thus given myself an 'out', my 'gut' feeling with this piece is that it is a cast copy or fantasy, made perhaps 200 or less years ago. It certainly appears that way to me; most of the details are rather fuzzy, indicating a cast copy.
The two examples pictured seem to be from the same mold. That is perhaps not surprising. Genuine or not, there would most probably have been one mold only.
Seth W. Stevenson in his book
'A Dictionary of Roman Coins' (929 pages, first publ. 1889),
has a four page essay on the subject of Roman medallions.