I'm trying to reduce my dependence on caffeine from needing ~160mg in the morning to needing 80mg. My strategy is to slowly reduce my intake, dropping maybe 20mg every 3 days. So far so good. 

But sometimes I feel tired later in the day, and also want caffeine. So I have 80mg more, 10 hours after the morning 160mg. Is this going to screw up my attempt at tolerance reduction? 

The argument for Yes: Daily caffeine intake is what matters. You can't reduce yourself down to needing less than 160mg in the morning by taking 240mg a day.

The argument for No: The important thing is the max amount of caffeine in you at any given time. Since the half-life of caffeine is between 1.5 and 9.5 hours (with a middle guess of 5 hours), by evening, you only have 160mg * 0.5 * 0.5 = 40mg in your system. Adding 80mg brings you to 120mg. This is less than the 160mg max dose your body is used to hitting, so it's not a big deal. As long as you keep the maximum caffeine in your system below 160mg, you can keep reducing your tolerance.

Which of these arguments is more right? Or is there a third view of the situation, better than either?

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Reference: https://examine.com/nutrition/how-caffeine-works-in-your-brain/

So, we see three vectors of caffeine dependence:

  1. You aren't getting enough sleep, and your adenosine level at 6 am is increasing from day to day, requiring a higher concentration of caffeine to out-compete it.
  2. Your brain makes more adenosine receptors to accommodate the large concentrations of both caffeine and adenosine in your system, so you again need a higher concentration of caffeine molecules to keep your brain from getting enough adenosine signals. This theory is supported by at least one paper: https://www.sciencedirect.com/science/article/abs/pii/002432058590325X
  3. Your rate of adenosine production AND destruction goes up, so you need a higher dose of caffeine to compensate for the larger swings your body is generating. This is just an alternate mechanism for "building up resistance" and would have the same remedies as #2

For case #1, you just need to get more sleep. This could be a typical pattern for people who drink coffee T-F and then sleep in on the weekend - their body resets and a little boost is sufficient.

For case #2, it's about the concentration of caffeine + adenosine in the bloodstream, over time (since it takes ?hours? to form or deconstruct adenosine receptors - regardless it's not instantaneous). Taking more caffeine in the afternoon is counterproductive, since it is maintaining the same high blood concentrations of active molecules. To reduce resistance you need to give your body time at low levels of stimulator molecules so it gets rid of the excess receptor sites.

In conclusion - don't use caffeine in the afternoon if you are trying to reduce your need for it

The focus on caffeine's effects through their action on adenosine binding is a useful frame that I hadn't been thinking in terms of - thanks!

However, when you say:
Taking more caffeine in the afternoon is counterproductive, since it is maintaining the same high blood concentrations of active molecules. To reduce resistance you need to give your body time at low levels of stimulator molecules so it gets rid of the excess receptor sites.

If I take caffeine in the afternoon, like, 4 hours after the morning dose, sure, I get it, that's bad. But if I take it 10 h... (read more)

Adosyne builds up over the course of the day. Your brain makes more receptors when there is more of the applicable agent around. So, if you have morning level of Adosyne + 120 mg caffeine in your blood in the morning, and afternoon levels of Adosyne + 80 mg caffeine + residual in the afternoon, that is going to keep the "need for receptors" high throughout the day. Then, also, having caffeine in your system as you sleep will also keep more receptors around until the morning than happens for people without caffeine in their system.
1Maxwell Peterson2y
That helps me better see what you mean - thanks.

Thanks! I’ve been vaguely thinking I’d like to be able to cycle but I think I have to reduce my dependence first, to not be dead on the off days.

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MikkW has been replacing caffeine with theobromine from cocoa powder, which (anecdotally) has been working better (an energy boost without the negative side effects), and is also supposed to be less addictive than caffeine. This at least suggests the possibility of replacing some caffeine with cacao. I've also started experimenting with it.

Very interesting! Thanks!

If you're able to adjust by 20mg/3 days, it seems this question can just be tested directly.  I look forward to hearing how it goes, and how it compares with any advice you get.

I’m actually not sure I can and it feels rough already to decrease. My “so far so good” was more meant as like… “so far, logically straightforward”, not “so far, good clear progress”. My life is a little bit consistently worse under these decreases and I do want to finish the reductions sooner rather than later, without accidentally burning progress through use of night caffeine.

Ah, I see.  It's been a long time since I've tried to moderate my consumption, but when I did (and when friends have done so), the metric was "total consumption per day", so I don't have much evidence either way whether the distribution across time matters.  The preferred way to reduce was to cut out non-morning intake, then to reduce late-morning intake, then to taper and remove initial-morning intake.  This can be done by brewing a mixed decaf/caf blend, and making it weaker (more decaf) after your first.

https://www.ncbi.nlm.nih.gov/books/NBK223808/ gives some data about metabolic clearing rate of caffeine (1.5 to 9.5 hour half-life, not very helpful, but if you're at the midpoint of that (5.5 hours to clear half of the caffeine in your bloodstream), that implies your afternoon dose is on top of significant remnants of the morning, and "total daily dose" matters more than "max ingestion at any one time".  

I've been wondering the exact same thing, thanks for asking.

[note: moved answer to comments]