Legal Question in Landlord & Tenant Law in California

Three day notice to conform to the lease or move. If he smokes after the three days you can file an unlawful detainer immediately.

First try talking to him and see if you can get him to stop. I am sure that he will not, but it is always best to do so. Then make sure the other roommates sign declarations about his smoking and drugs use before he is served with the three day notice, and then get them to sign amended declarations that he continued through the three day period, as you have no direct knowledge unless you can smell the odors directly and you do not want to go to court without evidence. Point out to him the disadvantages of getting a judgment against him in order to try to get him to leave. You might even want to give him a small bribe after he leaves to save the costs of going for an unlawful detainer [he will likely stop paying rent once served].