This is controversial.
I am about 60% confident about the following argument.
I design two thought experiments to better understand the moral implications of drinking, driving, and killing, or all those similar situations where you voluntarily put yourself in a state of altered consciousness, and then commit something terrible.
Though experiment number 1. There is a red button in front of you. If you press it, you will perform an action: you will initiate an action, and you won't be able to stop it until the selected action is completed. You being conscious or not of your action is irrelevant. What is important is that you cannot control your body doing the action. The actions are randomly chosen across all the possible actions that a drunk person does. Most of these actions are harmless: most of the time you just have a nice night out with your friends, some time you'll do something stupid like getting a tattoo, but in a few cases you'll do something terrible and kill someone. You don't have to press the button.
If you do, and you end up killing someone, did you make an immoral choice?
My intuition says yes, and I bet yours does too.
Though experiment number 2. There is a blue button in front of you. If you press it, two actions can happen: 1) with 99% of chance, 10'000 people with incurable cancer will be cured immediately, or 2) with 1% of chance, 1 random person in the world will die. You don't have to press the button.
If you do, and you end up killing the one person, did you make an immoral choice?
My moral intuition says no. My moral intuition says that the immoral action is not pressing the button. But saying no to this though experiment changed my point of view about the first one.
The second though experiment suggests that we shouldn't morally judge people based on the outcome of their action. Their outcome may be just based on luck. We should morally judge them based on the integral over all possible outcomes from their action.
How is this connected with drinking and driving? Assume that when you get drunk, you enter in an altered state of consciousness. Within this altered state, someone is obviously doing an action, and this someone inhabits your body, but is not you as his/her mental state is substantially different from your average mental state. If this is true1 you shouldn't be judged based on the action itself (since is not you doing it), but you should be judged based on the decision of entering this new mental state (giving the reins of your action to drunk you). I argue that the way to judge this decision morally depends on all the possible outcomes estimated at the moment you are getting drunk.
To answer the question in the title:
Your moral responsibility in this case depends on the state of the world when you take the decision to get drunk 2. If you are about to drive home and now you get drunk, you are as more morally responsible as if you got drunk at home, alone, whatever is the outcome of your action. Let me spell it clearer: if you drink, drive, and not kill, you are as morally responsable as if you drink and drive3. Even more: if you are about to drive, but not driving yet, and now you get drunk, you are in the same moral landscape as someone that had now decided to drive, and ends up killing someone, even if you decide not to drive4.