Chatting to a scientist at a party
When at a party and asked about body clocks alcohol is a great example to explain how our bodies respond to drugs differently at different times of the day (and no-one wants to be stuck talking to a scientist who doesn't have fun facts about their research). In Part 1 I've explained how our body clock can change how we respond to alcohol, but the same also works in reverse: alcohol affects our body clock with both short-term and long-term consequences.
Alcoholics often suffer from mood and sleeping disorders, and this could be exacerbated by how their own body clocks are damaged by chronic alcohol abuse.
Scientists look at the hormone melatonin to monitor body clocks. Melatonin is normally released only at night, and can be measured from urine samples, so it is a good and reliable indicator of an individual's clock time. In chronic alcoholics, their melatonin secretion is completely reversed: they produce it during the day! 
Melatonin rhythms are not affected in non-alcoholic healthy adults that drink alcohol , however, alcohol can still have a short-term disruption on body temperature rhythms. Normally, there is a 24-hour change in our core body temperature, dipping to its lowest of 36°C at 4am, and peaking during the day at around 37°C. Our body tries to keep to these temperatures by sweating when it's hot and shivering when it's cold etc.
Alcohol is thought of as a hypothermic agent, it makes your body cold, and hypothermia is an indicator of alcohol toxicity. Oddly however, taking alcohol at night time (when you should be asleep) raises body temperature. Drinking alcohol can change your body temperature's 24-hour profile.
A study was done on 9 healthy, non-alcoholic males, who had the arduous job of lying in bed all day and hourly either taking fruit juice or fruit juice and ethanol (to try and make it so they wouldn't know which they were taking). Their core body temperature was measured every 20 minutes (the old-fashioned rectal way), and it clearly shows that alcohol during the day lowers body temperature, but at night alcohol raises body temperature .
Alcohol changes the body clock's 24 hour temperature profile. Adapted from Danel, 2001
This is an excellent example of why a drug should be tested for its effects on the body with a complete 24 hour profile, not just seeing what its effect is during the day. For users, it warns us to be careful when drinking during the early hours, or even when our body thinks it's the early hours of the morning, such as shortly after a transmeridian flight. The effects of alcohol are not the same during the day and the night.
To sum up: body clocks can alter how we can tolerate alcohol, but alcohol in turn can alter our body clock.
 G. Murialdo, U. Filippi, P. Costelli, S. Fonzi, P. Bo, A. Polleri, and F. Savoldi, "Urine melatonin in alcoholic patients: a marker of alcohol abuse?," Journal of endocrinological investigation, vol. 14, Jun. 1991, pp. 503-7.
 T. Danel and Y. Touitou, "Alcohol consumption does not affect melatonin circadian synchronization in healthy men.," Alcohol and alcoholism (Oxford, Oxfordshire), vol. 41, 2006, pp. 386-90.
 T. Danel and C. Libersa, "The effect of alcohol consumption on the circadian control of human core body temperature is time dependent," Am J Physiol Regul Integr Comp Physiol, 2001, p. R52-R55.