Two of the most widely used drugs can affect sleep latency and sleep architecture. Individuals' reactions to these substances vary widely. Some people cannot handle a little caffeine right before bed without tossing and turning all night. Others feel little effects on sleep from caffeine and some say sleep better after a cup of coffee. Don't be skeptical of these claims. It's quite common for people to experience subjectively better sleep on caffeine. This should not be so surprising as caffeine is a stimulant and as as we have seen, sleep is a dynamic process during which the brain is active. Caffeine serves to suppress the neurotransmitter adenosine which does make us sleepy. But getting to sleep and staying asleep is a more complicated than just increasing adenosine levels.
However, at the first sign of insomnia, one tactic is to cut caffeine consumption so even if you are one of those people who normally has no problem with caffeine, pay attention when experiencing difficulty sleeping.
Alcohol is a depressant and often consumed in the evening. It is associated with sleep in the popular imagination, but alcohol is not a good candidate to replace prescription sleep aids in the larger insomniac population. For one thing, the effects of alcohol vary from person to person a lot more than the effects of non-benzodiazepine sleeping pills. And even though alcohol tends to relax people and may shorten sleep latency, it also tends to shorten time spent in slow wave sleep. This often leads to nocturnal awakenings. The person wakes up unrefreshed. The syndrome we call hangover is a bunch of symptoms and sleep inertia, sleep debt, and daytime sleepiness can be part of that.
Drunk driving and drowsy driving are twins. Both are dangerous risky behaviors to both the driver and other cars on the road. What is less appreciated is that they so often happen at the same time. Drinking happens more often at times of day (night) when sleep is normal. A night out often includes drinking past the normal bedtime. Police who stop dangerous drivers are more likely to charge a driver with DUI/DWI than with drowsy driving even if the driver is both sleepy and drunk. The policeman is just doing the logical thing. Few jurisdictions have specific laws against drowsy driving (although this may be changing). Officers generally can ticket or arrest drowsy driving under laws that cover disorderly or dangerous driving, but these are generally easier for the driver to get out of during the legal process than drunk driving. A DUI.DWI is a safer bet for law enforcement. Further, there is no easy roadside test for drowsy drivers. Drunk driving can be established by a breath test or blood test but there is no biomarker for sleepiness. And behavioral tests of wakefulness or the equivalent of sobriety tests like walking the line - those tests eventually might work but the problem is the person wakes up when he sees the flash of the police car lights in his rear view mirror.
It only makes sense for the police to pursue a DUI/DWI over a drowsy driving charge; hence higher reported rates of DUI.