Hi dear, yes it is very troublesome to see your mate being a habitual drinker. It is very difficult to clean them off this habit of theirs.
Next Steps
Talk to him if he is suffering from any issues at workplace, other tensions bothering him, offer him help etc. Be optimistic n make him feel valued.
Health Tips
Make him food he likes. U could add some natural powder in his drink to either cause him diarrhoea or loose stools. Please do consult here for further details.