I'm not sure that there's an official viewpoint (someone correct me if I'm wrong) but I think it's anything goes provided you're not harming yourself or anyone around you. Respect for human life is an essential Catholic dogma, so engaging in any activity that is harmful would be frowned upon. I've known plenty of priests to have a drink or two and the occasional flutter (eg St Patricks Day) but I'm sure there are plenty of others who abstain too.