How do I tell my employer I need time off for treatment?

I did exactly this two years ago. Short version: I went to HR, not my manager, and said 'I need to request medical leave for a health condition.' That's the whole sentence — you don't have to say the condition. If your company has 50+ employees and you've been there a year, FMLA generally protects your job for up to 12 weeks unpaid (check your eligibility — HR has to tell you). Mine also had short-term disability that paid part of my salary. The conversation I dreaded for months took eleven minutes. Nobody at work knows why I was out, and I still work there. Getting help protected my job — the drinking is what was going to end it.