Morning coffee really does "turn on joy": the effect is stronger in the first 2.5 hours after waking up

If you smile after your first cup, it's not just the placebo effect. Scientific Reports published a paper by a team from Bielefeld University: in two independent "real life" studies, scientists tracked the connection between moments of caffeine consumption and people's current emotions over the course of weeks. The conclusion is simple and practical: caffeine is consistently associated with an increase in positive affect (inspiration, satisfaction), especially in the first 2.5 hours after waking up; there is no such pattern for negative affect (sadness, irritability). Moreover, personal characteristics - from the usual dose of caffeine to the level of anxiety/depression and quality of sleep - hardly changed this connection.

Background

Caffeine is the most widely used psychostimulant on the planet: most adults use it daily, mainly for its alertness and “mood-boosting” benefits. However, for decades the literature has painted a mixed picture: in laboratories, caffeine almost invariably increases alertness and subjective energy, but some of the effects on performance and mood in coffee regulars were attributed not to “pure” stimulation but to the relief of withdrawal symptoms after an overnight pause (headache, lethargy, irritability). So it remained unclear to what extent caffeine in real life is associated with positive emotions and whether it influences negative affect – sadness, anxiety, irritability.

Another important uncertainty is the time of day. In the morning, most people experience sleep inertia—a brief decline in attention, mood, and reaction time immediately after waking, especially if the person woke up close to circadian zero or after a sleep deficit. Caffeine has been suggested as one of the few practical countermeasures, but the data on when (or whether) it provides the greatest emotional benefit are patchy. This makes key questions about timing of use, context (fatigue, social environment), and individual differences.

The methodological field is also changing. Instead of one-time laboratory tests, experience sampling / ecological momentary assessment is increasingly used - multiple short surveys on a smartphone in a natural environment. This design allows us to catch the "micro-effects" of caffeine on emotions throughout the day, and not just in standardized conditions, and to check whether the connection depends on sleep, the usual dose of caffeine, anxiety / depression, etc. This approach formed the basis of a new study in Scientific Reports, where three ideas were tested on two independent samples of young adults (14 and 28 days of observation, >28 thousand reviews): (1) is caffeine associated with an increase in positive affect; (2) does it reduce negative affect; (3) does the strength of the connection change depending on the time after awakening and personal characteristics.

The results are especially important in context because emotional well-being varies greatly depending on sleep and circadian rhythms: sleep deprivation increases negative background and inflammatory markers, late rising and sleep structure are associated with the severity of morning inertia, and daytime mood swings have stable diurnal dynamics. Against this background, a “real-world” assessment of caffeine’s contributions is a chance to separate routine (“removal of undercaffeination”) from a true rise in positive affect, to see windows of greatest benefit, and to understand who and when caffeine really helps noticeably.

It is these gaps—pure emotional effect vs. withdrawal, the role of time of day, and ecological validity—that provide the scientific background for the study, which found that caffeine was consistently associated with an increase in positive affect, especially in the first ~2.5 hours after waking, while no systemic effect was found on negative emotions.

How was this tested?

• Design of "everyday experience". We used the "experience sampling" method: the smartphone asked short questions "right now" several times a day.
• Two samples of young adults: 115 participants aged 18–25 (14 days, 8,335 responses) and 121 participants aged 18–29 (28 days, 19,960 responses).
• What was recorded: in each survey - whether there was just caffeine (any source), levels of positive and negative affect, fatigue, social context (alone/with others), whether it was a work day, etc.
• Key time variable: how many hours have passed since awakening (0-2.5; 2.5-5; …; >12.5 h).

An important advantage of this approach is its ecological validity. This is not a laboratory: no one is handing out pills or monitoring the lighting; scientists are looking at “real” life with its lack of sleep, deadlines, chats with friends and the occasional cappuccino. That is why the results are easier to transfer to everyday practice.

The main results - short and to the point

• Positive affect ↑ after caffeine. The relationship was present in both samples; most pronounced in the first 2.5 hours after waking up (probably helps to “overcome” sleep inertia). A moderate second rise appeared in the evening (10-12.5 hours after waking up).
• Negative affect - without a clear pattern. In one of the samples it decreased, but the effect was much weaker and unstable; in another - not confirmed. No systemic "anti-negative" effect of caffeine was found.
• Who you are is almost unimportant. Neither the usual "dose" of caffeine, nor the addiction/expected "withdrawal", nor depression, anxiety or quality of sleep changed the strength of the effect. That is, the context and state are more important than the "personality portrait".
• The context is important: the more tired a person is at the time of the survey (and even if he was tired minutes earlier), the stronger the "mood boost" from caffeine. But among people the "bonus" is weaker - it seems that sociality itself already supports positivity.

To avoid getting lost in the nuances, here is a “working version” of the conclusions about the time of day:

• Morning (0-2.5 hours after waking): maximum increase in positive affect after caffeine.
• Day (≈2.5-10 h): the effect decreases and is often statistically insignificant.
• Evening (10-12.5 hours): a small but significant “second hill” of positivity.
• Negative affect: there are no obvious “windows” - caffeine does not systematically extinguish it.

Why might this be?

Caffeine blocks adenosine receptors, increasing dopamine/norepinephrine - hence the vigor and subjective "lift". In the morning, this block is especially noticeable: we are just emerging from the "inertia of sleep". In the evening, social factors (coffee on the way to a meeting or before training) and the "second shift" of fatigue can also play a role. But negative affect is often "tied" to difficult contexts - chronic stress, events, well-being - and brief stimulation of the central nervous system does not erase it in itself.

What does this mean for the reader (and how to apply it without fanaticism)

• Looking for the "most effective" coffee? It makes sense to plan your first cup in the first 2.5 hours after waking up: that's when the effect on your positive mood is greatest.
• Are you sagging towards night? A small boost in positivity is possible 10-12.5 hours after waking up - but remember about sleep: late-night coffee can "eat up" the quality of the night.
• Tired - Will Help More If you are objectively exhausted, the "mood boost" from caffeine will probably be greater.
• Coffee is not an antidepressant. It has a weak and unstable effect on negative emotions; if the background of anxiety/melancholy persists, this is a task for sleep hygiene, psychotherapy and/or a doctor.

Important Disclaimers

• Self-reports and young sample. Participants self-reported whether they had caffeine and their emotions; both samples were young adults, so generalization to other age groups requires testing.
• No exact time or dose. The authors did not record how much caffeine was consumed and when (e.g. double espresso vs. tea).
• Chronotype was not measured directly. Owls/larks may have confounded the picture; objective circadian markers are needed in the future.

What will scientists test next?

• The first cup of the day and the "withdrawal syndrome". Divide the effect of "removing undercaffeination" and the actual stimulation.
• Objective data: sleep/heart rate trackers, accurate timestamps and caffeine doses.
• Age and clinical groups: does the same pattern apply to adolescents, older adults, people with depression/anxiety, shift workers?

Summary

Your morning coffee is indeed associated with a better mood - especially in the first hours after waking up; however, the "anti-blues" from caffeine is a myth or an isolated case. Therefore, it is wiser to get enough sleep, communicate and move, and use coffee as a gentle moderator of your day, and not as a "magic button of happiness."

Source: Hachenberger, J., Li, Y. M., Realo, A. et al. The association of caffeine consumption with positive affect but not with negative affect changes across the day. Sci Rep 15, 28536 (2025). https://doi.org/10.1038/s41598-025-14317-0