How much zanaflex will it take to kill you?

The manufacturer recommends that total daily dose should not exceed 36 mg. Additionally , the use of single doses greater than 12 mg is not recommended. Do not take more than three doses (36 mg) in a 24-hour period. Too much of this medication can damage your liver. - Source: Drugs.com

Thus, you shouldn't take it if you have liver problems and also limit use while drinking, please.