The overall goals of this study are to (1) expand knowledge about interactions of chlorzoxazone with alcohol by assessing the effects of chlorzoxazone compared to placebo in moderate and heavy social alcohol users and (2) to compare the effects of chlorzoxazone on visual cue induced alcohol craving to placebo in moderate to heavy social alcohol users.

The investigators propose a 45-day, double-blind, placebo-controlled crossover study in light to moderate and heavy alcohol users.

The specific aims are to:

1. Determine if chlorzoxazone alters daily alcohol consumption by comparing the mean drinks consumed per day during chlorzoxazone administration compared with the mean drinks per day consumed during placebo administration.
2. To determine if polymorphisms in genes encoding for neurotransmitters or receptors involved in alcohol reward, abuse, dependence, craving, or relapse may predict the level of response to chlorzoxazone's effects on alcohol consumption or craving.
3. To investigate any change in alcohol craving during a cue induced craving task where participants view and respond to a number of images.

Inclusion Criteria:

Inclusion Criteria: Healthy adults who are social drinkers 21 - 50 years of age.

1. Moderate to heavy social drinkers (women=10-25 drinks/week, men=14-30 drinks/week).
2. If female, must be non-lactating, not pregnant, and using a reliable contraception method (i.e. abstinence, intrauterine device [IUD], or hormonal birth control).
3. Able and willing to provide written informed consent.
4. Able to understand and follow the instructions of the investigator, and understand all rating scales.

Exclusion Criteria:

1. Use of cocaine, amphetamines, hallucinogens, "ecstasy", opiates, sedatives, pain pills, sleeping pills, or other psychoactive drugs more than twice a week.
2. A history of complicated alcohol or other drug withdrawal syndrome(s), e.g. delirium tremens or seizures.
3. Current physiological dependence on any psychoactive drug (except nicotine or caffeine) including alcohol, as determined by MD or NP assessment.
4. Current enrollment in an alcohol or other drug treatment program, or current legal problems relating to alcohol or other drug use, including awaiting trial or supervision by a parole or probation officer.
5. Currently trying to quit using alcohol and/or "recreational" drugs.
6. Clinically significant medical or psychiatric illness as determined by screening blood tests, medical history, and physical exam performed or reviewed by the study MD or NP.
7. Bilirubin more than 2 times the normal upper limit.
8. AST (SGOT), ALT (SGPT), or alkaline phosphatase more than 2 ½ times the normal upper limit.
9. Symptoms of liver disease, as assessed by MD or NP assessment (jaundice, Hx of hepatitis, itchy skin, etc.).
10. A current pregnancy, or a woman of child-bearing potential not currently using an adequate means of contraception.
11. BAC level greater than 0.05% at the beginning of Screening Visit, Visit 1 or Visit 4.
12. Neurological dysfunction or psychiatric disorder severe enough to interfere with assessment of outcome measures as defined above.
13. Known allergy to chlorzoxazone.
14. Has received an investigational drug within 30 days prior to Study Visit 2 (after screening visit).
15. Subjects who are unable to read or speak English.
16. Those who, in the opinion of the investigator, are considered unable to adhere to scheduled appointments, are unlikely to comply with the study protocol, or who are unsuitable for any other reason.

From enrollment through study completion, up to 45 days