When to drink coffee will not affect the night sleep.

The half-life of caffeine in the human body is between 2 and 12 hours. Although some of us metabolize caffeine faster than others because of genetic differences, the typical half-life of caffeine is about 5 hours. Caffeine usually stays in the body for 10 hours (or more) (technically, it takes up to five half-lives to remove drugs from the body).

So if you drink coffee at 7 p.m., by the time you want to go to bed at midnight, the caffeine in your body is still working on your central nervous system. Experience tells us that if you want to go to sleep at midnight and stay asleep, just to be on the safe side, you'd better not drink coffee after 2 p.m. (source: http://www.npr.org/). Of course, it also depends on your ability to metabolize caffeine.

In addition, studies have shown that high caffeine intake can affect REM sleep, which is also disadvantageous if you don't get enough sleep for a long time.

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1. For example, if the half-life of a drug is 6 hours (usually denoted by T1 dial 2), the blood concentration of the drug is half of its highest value after 6 hours; it is reduced by half again after 6 hours; and it is reduced by half again after 6 hours, and the blood concentration is only 1 / 8 of the highest concentration.

The half-life of the drug reflects the rate of elimination (excretion, biotransformation and storage, etc.) of the drug in the body, and indicates the relationship between the time of the drug in the body and the blood concentration, which is the main basis for determining the dose and times of drug administration. drugs with long half-life indicate that they are eliminated slowly in the body, and vice versa.

The half-life of each drug is different; the half-life of the same drug is not exactly the same for different individuals; and the half-life of the drug is different between adults and children, the elderly, pregnant women, healthy people and patients. The half-life of a drug is usually an average. In patients with hepatorenal insufficiency, the drug elimination rate is slow, and the half-life will be relatively prolonged (source: half-life).

At this stage, the activity of the brain's neurons is the same as when it is awake. Most of the vivid dreams that can be recalled after waking up occur during REM sleep.

Because REM sleep is very different from other sleep stages in physiology, the sleep stage other than REM is called non-REM sleep (NREM).

Often the former stage is shorter and the latter stage is longer. Humans usually wake up for a while after REM sleep, with about 90 to 120 minutes of REM sleep each night (source: REM sleep).