Between 30% and 60% of individuals who take cocaine combine its use with alcohol. Clinical studies indicate that concurrent use of alcohol and cocaine are associated with increased mortality and morbidity from cardiovascular complications, hepatotoxicity, and behaviors leading to personal injury. In 74% of cocaine-related fatalities in the US, co-ingestion of another drug, usually ethanol, is present. The addition of alcohol to cocaine increases the risk of sudden death by 25-fold.
The concomitant use of alcohol and cocaine results in the in vivo formation of a third active compound of toxicological importance, ethylbenzoylecgonine, which is commonly known as cocaethylene. Although its behavioral pharmacology and psychomotor stimulant effects are similar to cocaine, the toxicity of cocaethylene is much greater; compared to cocaine, its plasma half-life is longer and inferential evidence suggests that its LD50 is much lower.
In dog studies, cocaethylene has been found to be a much more potent precipitant of convulsions and cause of lethality than cocaine. Cocaethylene blocks sodium channels more potently than cocaine. Although the toxic level of cocaethylene in humans is not known, the LD50 in mice was found to be 93 mg/kg for cocaine versus 60 mg/kg for cocaethylene. The process of cocaethylene formation continues over several hours, which may explain why sudden deaths may occur 6-12 hours after cocaine ingestion.
Cocaethylene, which is ultimately metabolized to benzoylecgonine, is not the only factor operative in ethanol's augmentation of cocaine effects (Rose, 1994). Consumption of ethanol before cocaine use also increases the bioavailability of cocaine.
Signs et al presents an exception to the weight of the literature in a study based on 57 emergency department patients who tested positive for both alcohol and cocaine. In these patients, blood pressure (systolic and diastolic), heart rate, and body temperature did not differ significantly between those testing positive for alcohol and cocaine both and for drug-free controls. This may be because chronic cocaine users reportedly develop tolerance to the cardiovascular effects of the drug. Based on the study of 57 patients, Sign et al concluded that the incidence of serious cardiovascular complications resulting from simultaneous use of cocaine and ethanol does not appear to be significantly higher than that observed in patient populations with use of cocaine only, use of ethanol only, or no drug use.
Taken from
http://www.emedicine.com/emerg/topic102.htm, scroll to the bottom for an extensive reference list.
While no one can say exactly how much worse the combination is for you, I think it is safe to say that it is worse.