Both caffeine and alcohol have significant effects on sleep patterns.

Caffeine, a stimulant found in coffee, tea, energy drinks, and chocolate, can disrupt sleep by blocking adenosine receptors in the brain. Adenosine is a neurotransmitter that promotes sleep and relaxation. By blocking its receptors, caffeine can interfere with the natural sleep-wake cycle, making it difficult to fall asleep and reducing the overall quality of sleep. For example, consuming a cup of coffee in the afternoon can lead to difficulties falling asleep at night, as caffeine's effects can last for several hours.

On the other hand, alcohol is a depressant that initially may make you feel drowsy and help you fall asleep faster. However, it can disrupt the second half of the sleep cycle, leading to fragmented and less restorative sleep. This can result in waking up feeling groggy and tired, even after a full night's sleep. Additionally, alcohol can also worsen conditions like sleep apnea and snoring, further impacting sleep quality.

References:

1. "Caffeine and Sleep." Sleep Foundation. www.sleepfoundation.org/nutrition/caffeine-and-sleep
2. "Alcohol and Sleep." National Sleep Foundation. www.sleepfoundation.org/nutrition/alcohol-and-sleep