How does long-term use of caffeine affect productivity?

Since this study first came out, I've thought it was known that caffeine likely doesn't have any long-term benefits as a stimulant simply because of tolerance and withdrawals. Has anything changed since then?

I am trying to figure out whether caffeine helps productivity in the long run. Looking back 10 years from now, how much more/less productive will I have been if I were to drink coffee every day, or every second day?

While you're looking for studies, have you considered just starting a double-blind experiment? If you've read my page on nootropics, it should be pretty clear how you could do it with a water-soluble substance like caffeine and where you could get cheap bulk caffeine.

Am I the only one who finds it astonishing that there isn't widely known evidence that a psychoactive substance used on a daily basis by about 90% of North American adults (and probably by a majority of LWers) is beneficial if used in this way? What explains this apparent lack of interest? Discounting (caffeine clearly has short-term benefits) and the belief that, even in the unlikely case that caffeine harms productivity in the long run, the harm is likely to be small?

Your genome may have something to do with caffeine's long-term effectis. According to 23andMe, I have a variant of the marker rs762551 which supposedly makes me a "fast caffeine metabolizer." Apparently the alleles for slow caffeine metabolism can increase your heart attack risk from drinking coffee.

Reference:

Coffee, CYP1A2 genotype, and risk of myocardial infarction.

http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Search&db=pubmed&term=16522833

Anecdotally, it doesn't feel like I get overall improved functioning from caffeine, but I can use it to gain control of when my high-alertness and low-alertness periods will happen. This is 100% a must for the kind of shift work schedule I'm doing right now, which definitely was not intended for humans. I usually consume caffeine at work only and minimize it on my days off; ideally this adds up to consuming it on 4/9 days, in practice more because I take overtime. I take longer breaks whenever possible. Caffeine is pretty much what allows me to function during 12 hour night shifts.

I think that maybe if I could completely remove the effects of current caffeine dependence, I might be able to handle 12 hour day shifts (7 am-7 pm) caffeine free, but I'm not sure about that. Caffeine helps smooth out dips and slumps in my circadian rhythms, and I need all of the alertness I can muster to take care of humans on ventilators.

I basically gave up on caffeine almost a year ago. I've not noticed any overall changes, aside from not having an addiction. There is one short-term benefit that regular users seem not to have - if I've had a very late night or for some other reason I'm very tired but I need to keep going, I can take some caffeine and run normal(ish) for several hours. It's saved me a few times, I'd be disappointed to lose that tool.

I do miss the taste of coffee though.

I'm aware that my caffeine use might have little benefit to total productivity over the course of a week.

I do attach value to using caffeine to choose to be less susceptible to tiredness for the next few hours.

Does that make sense?

Long term caffeine tolerance can be problematic. To combat this problem, every 2-4 months I stop taking caffeine for about 2 weeks (carefully planned for less hectic weeks). In my experience and that of at least one other colleague this method significantly lowers and possibly removes the caffeine tolerance. Two people does not make a study, but if you need to combat caffeine tolerance it may be worth a try.

As far as I'm aware there are no long-term effects of caffeine that are positive for productivity, unless you count repeatable short-term effects aggregating over a long time period as a 'long-term effect'.

When I drank coffee for about a year, I didn't have any noticeable impairments, at least nothing that slapped me in the face.

The withdraws though... oh god the withdrawals.