If you have Deep Packet Inspection (DPI) enabled and own the PEF license, you can set rules to block peer to peer sharing; including bit torrent.
An example configuration in policy:
ip access-list session block-p2p
user any app bittorrent deny
user any appcategory peer-to-peer deny
However, be sure to enable DPI in the Global Firewall settings as well as the individual role.