The U.S. Food and Drug Administration banned ephedra in 2004 over concerns regarding severe safety risks. That ban did not apply to liquid infusions, or teas, made from the herb, because these are regulated as a food, not a supplement. Since then, ephedra has made its way into alcoholic beverages by way of energy drink mixers. Because alcohol depresses the central nervous system while ephedra stimulates it, the results can be unpredictable and dangerous.
As the ephedra stimulates your CNS, it masks the depressant effects of the alcohol. You'll feel more sober than you really are -- although you may feel like you've got it together, the ephedra does nothing to counteract errors in judgment and motor control produced by the alcohol. You may feel that you're fine to drive, even though your actual driving skills are still reduced to a level proportionate with the amount of alcohol you ingested, leading to potentially disastrous consequences. Even if you don't drive, you won't realize how intoxicated you are, which could lead you to drink more than you otherwise would. This puts you at risk for alcohol poisoning, which can be fatal.
Alcohol and ephedra have opposite effects on the body, and sending mixed signals to your brain causes unpredictable reactions. Whether the alcohol or the ephedra causes the dominant effect depends upon the dose of each and your individual constitution, but the interactions between the two can take the form of heart failure in severe cases. In less-severe cases, the reaction can land you in jail -- a 2001 report in the journal "Medicine, Science and the Law" outlines the case of a man who combined alcohol and ephedra, resulting in a temporary psychosis on two different occasions. Each occasion ended with a criminal conviction, large fine and mandatory twice-weekly alcohol tests. The man had no history of mental instability prior to these incidents.
Combining ephedra and alcohol leads to a worse morning-after for two reasons. First, you are more likely to drink more than your body is used to or can handle, because the ephedra makes you feel less drunk. Second, both ephedra and alcohol are dehydrating, and dehydration is one of the major causes behind hangover symptoms. It's not your imagination -- you really do urinate more when you drink, and ephedra intensifies this diuretic effect. If you overindulge, the dehydration becomes extreme and greets you the next day with a pounding headache, nausea and a general "sick" feeling that is compounded by the typical hangover feeling caused by the alcohol being processed from your body.
Mixing alcohol with any kind of stimulant is not safe. In fact, several states have banned premixed drinks of this type. Decide whether you want a stimulant or a depressant, and stick with your choice. As far as stimulants go, ephedra isn't the smartest choice due to the known side effects -- just because one form of it escaped the ban doesn't make it safe. Use caffeine instead -- although it can still cause negative side effects in high doses, it is more widely studied and understood than ephedra, and can be used by most people without risk. Alcohol is legal for those over 21, but again, that doesn't mean it's safe. Always drink responsibly and never drive when you've been drinking.