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Comment by danieltillett | Hacker News Reader

The thing to remember with caffeine is its half-life in non-smokers is 8 hours (it is 3 hours in smokers). I have a rule to never have any drink with caffeine after midday - if I break this rule even by an hour I suffer that night and the next day. Caffine is a morning drug.

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This is highly personal, and there's no substitute for experiment. My rule is no (caffeinated) soda within an hour of bedtime, and no coffee within 3-4 hours, so the variation is wide. I don't smoke, by the way.

As an aside, the whole "8 hour half-life" is astonishingly high, to me. Caffeine is nice, but it doesn't seem to have that strong an effect on me, and certainly nothing I notice 5-8 hours after. I drink quite a lot of caffeine these days, but even at times when I went off caffeine for a few weeks, I didn't get effect durations any longer than 1-3 hours.

As you say, the variation is wide. I can drink tea up until about 6pm without any problems, but if I have even one coffee after lunchtime I'm going to be up half the night regretting it.

It's the opposite with me. I can have coffee in the late afternoon, in some cases even in the evening, without problems--but if I have a tea after 3 pm or so, I'm sure to have trouble.

Might have something to do with the strength of the tea, though.

Depending on the type of tea you drink, this could be due to the calming effects of l-theanine [1] in tea.

I have the genes that extend caffeine half-life. If I drink an American large coffee, I get anxious. I can drink a whole pot or two of green tea and feel a nice lift in mood.

As others have mentioned, any coffee after noon and I can't fall asleep until around 2am. I avoid caffeine most days except for the occasional morning kombucha.

[1] https://www.reddit.com/r/nootropics/wiki/faq#wiki_l-theanine

There's also a gene that determines if you're a fast or slow metabolizer, I think it affects half life by around a factor of two. 23AndMe checks the associated SNP.

Yes this is true. I should have added these times are averages, not constants.

Metabolism of drugs like caffeine is genetically quite variable and is quite an issue for pharmaceutical companies.

you may want to rethink that practice after having a look at this: http://www.ncbi.nlm.nih.gov/pubmed/7796154

short summary: 200mg at 7 a.m., and going to bed at 11 p.m. had following effect: "Compared to placebo, sleep efficiency and total sleep time were significantly reduced."

I can drink coffe at night before going to bed and still sleep like a baby. I wonder if something is wrong with me.

Built-up tolerance? After drinking triple espressos like water in university I could drink coffee at 10 pm and still fall asleep an hour later. Of course, I'd wake up feeling more tired than before with a splitting headache, but that's what the triple espressos were for.

For me I've found that it takes a while to take full effect. I normally go to sleep around 9:30. If I drink a cup at 9pm I'll fall asleep okay at 9:30. If I drink a cup at 6pm, I'm going to have problems sleeping.

It varies a lot per person.

The effects are 6 hours for me, less than 1 hour for my father (who smokes), and can last over 18 hours for my wife and mother-in-law.

I haven't seen the studies on caffiene half-life, but I suspect the variation is very high.

I personally take it early morning and after a siesta.

Yes! When I have coffee after ~14:00, I have trouble falling asleep at night (even though I am a smoker, then again, I am not exactly a chain smoker).

Green tea is less of a problem (then again, the way I prepare it, it contains much less caffeine).

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