I have been known to have a bloody mary with breakfeast (Hey, tomato juice is a breakfast drink-- the vodka is incidental)... often.
Seriously, the bottom line is this- drinking is like anything in life: it's up to you to be responsible about it. I've known a guy who was a multimillionare software developer who spiked his coffee every single morning. I've also known total screwups who couldn't hold a job, but hadn't touched drugs or alcohol even once in their lives.
The key is knowing yourself. If you're going to have to be coherant (and that includes for simple tasks such as DRIVING) at some point later in the day, you probably shouldn't be putting away a half-rack beforehand.
And if you can't stop yourself, you need to see somebody about it.