I've heard this over and over, but as far as I can tell, caffeine = caffeine = caffeine. I'm not a chemist, but I can't find any mention of any different forms -- it's C8H10N4O2. [1]
Is there any scientific evidence that alertness is related to anything but the quantity of caffeine, regardless of whether it's delivered as black tea, mate tea, coffee, pills, etc.? Assuming that the caffeine makes it into the bloodstream at the same rate?
But if a Coke is ~3mg caffeine 100ml and coffee is ~40mg per 100ml, drinking 13.3 "units" of cokes will not be equivalent to 1 "unit" of coffee.
1. Timing of the intake will affect the efficacy (x mg of caffeine over 2 hours vs. 20 minutes is very different to the body)
2. Controlling for time-dependent intake (the spherical human consumed both quantities instantly), concentration of the substance affects the rate / efficiency of absorption by the body (I cannot predict for which way it will go, this stuff is complex) so the net absorbed caffeine will be different between the two substances
3. Delivery mechanisms are different: Coke is very sugary, black coffee is not and is a colloidal suspension. The local chemical environment for the caffeine within these two substances will be different. Sugar is known to affect osmosis, meanwhile who knows wtf the gunk in coffee is doing at the chemical level.
So to sum up "caffeine = caffeine = caffeine" is probably a useful rule of thumb and will get pretty far, but at the physiological/biochemical level, that is as useful as armchair pseudoscience is.
To use a possibly relatable issue: most people find consuming shots of vodka more efficacious than consuming the equivalent amount of beer by alcohol. 3 shots will probably get you more wasted than necking 3 beers
But it won't, after drinking 3 beers after each other your BAC will go to the same level, just takes a little more time to get there.
Subjectively, you start feeling drunk much more quickly because the change is faster with Vodka, but your capabilities are as much impaired.
Though my intuition tells me that chugging three beers would get me more drunk than drinking three shots. Sigh. The things I do for science.
The obvious question is what you're drinking - with the rise of craft beer scene, 3 beers could easily be substantially more alcohol than 3 shots. But assuming you match alcohol volume and consumption speed, absorption rates can still vary substantially.
From what I can find, it looks like beer actually would get you (and everyone) more drunk: diluting alcohol substantially speeds up absorption, and carbonating dilute alcohol probably does also.
I know it was just an example, but after looking into this earlier this year, coke and pepsi have a much higher caffeine content at 10mg/100ml and 13mg/100ml (for coke and pepsi respectively)
The espresso I drink never contains sugar or milk.
The coca cola zero I drink doesn't contain sugar either.
I cannot stand the highs and lows of sugar. I notice it especially at birthday parties. I mean, its already boring... and them comes up of the sugar rush followed by a low where I start yawning and feeling sleepy. I so not wanna be there anymore at that point.
The general trick though, is dosages. You want to keep it stable when it matters, and at the end of the day wind down. Which means you do not want to drink caffeine drinks anymore in the evening.
For the rest, I can highly recommend mindfulness to help increase focus (but before I started it, I found it super annoying when someone suggested it and then I tried it myself and it didn't work out; so I am following a course on it, for people with autism). Meds can help out as well.
Their site says it contains 27g sugar/8.4 fl oz. Pretty sure sugar is a stimulant.
For me, the same whisky has very noticeable differences in the effect and after-effect depending on how it's served / mixed.
That's a big if. Others have listed a few factors to consider, another example is Guaraná powder which contains a lot of fiber, thereby slowing the caffeine intake.