When you are dealing with an individual who is struggling with a substance abuse issue, you’ll likely feel the need to set some boundaries for yourself.  I’m sure you can find 50 counselors who would tell you different, but I strongly advise against creating a home contract.  It may seem like a good idea to clearly express specific expectations in writing, but it’s gonna backfire on you.  Here is why…
1.  Wake up… You are dealing with addiction!  Addiction doesn’t play by any normal universal rules and it certainly isn’t going to abide by some silly home contract. I know you think that having the person sign their name on a piece of paper makes it “official” and that it will carry more weight, and that will certainly make them understand that you “mean business,” but the whole process is demeaning and irrational.  Having them sign their name on a piece of paper will not make them more likely to follow the rules, but will probably make them more likely to resent you.
2.  You are only going to back yourself into a corner!  I’ve been working with addicts and alcoholics for years and here is what will actually play out: The addict/alcoholic will be able to rationalize any decision or breach of the contract, but if you don’t follow it to the letter of the law, they will make sure to hold you accountable.
Here’s an example:
Let’s say you tell your loved one that they can’t drive the car if they fail a drug screen.What’s going to happen when you know for sure they have used but it’s not showing up on the screen (there are about a million ways this can happen).Now you are in a situation where you can’t prove it.They are going to back you into a corner by saying “you said as long as I passed my screens, I could drive.”Now, you have to stick to your word (you’re not nearly as good of a ninja rationalizer as the addict/alcoholic so you’re not gonna win this game).
Or here is another:
Let’s say you tell your loved one that if they relapse one more time they can’t live in the house.Now you have set up a scenario that is going to promote more lying and hiding.If the person messes up, they aren’t going to tell you! Or maybe you find out that they did have a lapse, but you really do think they are trying and they have learned from it. Now you’re backed into the corner again!
Making a home contract doesn’t make the person more likely to comply, but it will very much take your power away.  I advise family members to reserve the right to make “game time decisions.”  This disease is CUNNING AND BAFFLING!  You never know what kind of scenario you’re gonna end up with so leave your options open!
I’m not suggesting that you don’t have any boundaries or limits.  I’m suggesting you empower yourself to make whatever decisions you need to based on any given situation that comes up.  YOU DO NOT HAVE TO “GIVE A HEADS UP.”
 
Consider making  more general statements like “It’s your job to convince me that it’s a good idea for you to be driving”.  The difference here is that you are making it clear that the person isn’t entitled to driving privileges, but also leaves you the flexibility to make whatever judgement call you feel appropriate.
Boundaries should be about you, not about them.  If you want to make a contract, then make one for yourself. Make some decisions how you want to behave.  Write that down and sign it, or tell someone who will hold you accountable.  For example, you might want to make a contract with yourself that you won’t put yourself/family in financial jeopardy because of the person’s addiction, or you won’t allow yourself to ignore other important aspects of your life because of another person’s addiction.  If you make these promises to yourself, the decisions will be much clearer when the time comes to make hard choices.