Taking as a parameter the first sip of coffee we drink, and taking 10 minutes to drink a cup of coffee, how soon are the effects of caffeine to appear?
I'm sure there are a lot of studies out there - but ultimately it's personal. It's like asking, how long after drinking a glass of wine do you start to feel the affects?
Averages can be arrived at but ultimately everyone is different.
As for me, it may be psychological, but I start to feel the affects seconds after my first sip. (Assuming it's high octane coffee and not the lukewarm water found in some diners.)
I've seen several articles say that coffee takes ten minutes to kick in. Others say 45 minutes.
I don't know how they're measuring things but speaking for myself, and numerous others, the psychological affects kick in much sooner. I don't think coffee would be as popular as it is if it took 10-45 minutes to kick in.
It takes around 45 – 60 minutes for caffeine to kick in after it is consumed. https://www.scienceabc.com/humans/how-does-caffeine-work-affect-brain-body-adenosine-receptors.html
see also: https://www.caffeineinformer.com/caffeine-metabolism and: http://www.dailymail.co.uk/health/article-1100767/A-cup-coffee-works-just-10-minutes-drink-greater-impact-men.html
The scienceabc.com article continues with:
One of the reasons coffee remains so popular is that the effects of caffeine can often be felt for 4-6 hours.
4-6 hours? Ha. Maybe in a controlled environment, where one can measure things to the last drop. In the work environment coffee addicts need to a boost in far less time than that.
The effects of coffee is (if not solely) mostly related to caffeine. The science that considers the effect of any chemical on human body is known as pharmacology. As a branch of this, the science that analyzes temporal effects is known as pharmacokinetics.
Therefore, I would like to provide a EU resource on pharmacokinetics of caffeine as it is from a more trustworthy body.
According to this presentation, the absorption of caffeine is around 30-120 minutes. Means, it takes half an hour to two hours to feel a cup of coffee's effect.
It adds caffeine passes through any bodily tissue, and totally absorbed.
Then, it has an half life of 2-8 hours to metabolize. This means, human body gets rid of half of the caffeine in 2-8 hours.
(But it doesn't mean it gets rid of all of it in 4-16 hours. As the amount of caffeine decreases, human body cares less about it in the next cycle and gets another half at each cycle. Think like that.)
So, a cup of coffee's effect may remain a few hours for some or during the day for some others.
A study was conducted by the University of Barcelona and published in 2008. The Stanford Sleepiness Scale was used to asses the decrease in somnolence induced by caffeine pre-consumption, post 10 min, post 20 min, and post 30 min. Scores for "subjective activation" were also recorded at the same intervals.
Many previous studies assessed the effects of larger than normal amounts of caffeine 30-40 min after consumption whereas this study focused on the appearance of early responses in the subjective state associated to caffeine at typical doses between 100-250 mg.
According to the study:
The appearance of such effect in our study was very quick, at 10 min after caffeine intake, and then it progressively increased at 20 min and showed the highest effect at 30 min post-administration.
They also mention that the results were similar to other studies conducted in 1998 and 2000 which state that the levels of caffeine may already be 50% of Tₘₐₓ within 10 min post-consumption, reaching a maximum plasma concentration (Tₘₐₓ) around 30-40 min after oral administration.
It should be noted that the effects were documented or recorded at 10 min post consumption (50% Tₘₐₓ), meaning that the initial effects can be felt at least 10 min after drinking coffee but maybe sooner at 20%. Caffeine is one of those drugs that your body quickly adjusts to which is why the effects wear off when the blood concentration falls to 50% roughly 5 hours after consumption but when you reach an initial concentration of 50% or less, it can be noticeably felt.
So, if it takes you 10 min to drink a cup of coffee, you may begin to feel the effects as soon as you are finished with your first cup. The full effect (at least 75% Tₘₐₓ) may be felt after an additional 10-25 min.