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Why does coffee make me sleepy instead of awake?


Coffee is known for its ability to provide an energy boost and increase alertness. However, some people experience the opposite effect – feeling sleepy after drinking coffee! This can be perplexing, especially if you rely on your morning cup of joe to help you start the day feeling energized. So why does coffee make some people sleepy? There are several potential reasons.

Caffeine tolerance

Caffeine is the main stimulant found in coffee. It works by blocking adenosine receptors in the brain. Adenosine is a neurotransmitter that promotes sleep. When caffeine blocks adenosine receptors, it causes neurons in the brain to fire more rapidly. This stimulates the release of other neurotransmitters like dopamine and norepinephrine, which boost mood, focus, energy, and alertness.

However, with regular caffeine consumption, your body can build up a tolerance. This means it takes higher amounts of caffeine to get the same stimulant effect. If you’ve built up a strong tolerance, coffee may no longer provide the energizing boost it once did. The dose you used to rely on just makes you feel normal, while higher amounts can lead to jitteriness or anxiety.

Some signs of caffeine tolerance include:

  • Need more coffee than you used to in order to feel alert
  • Experiencing caffeine withdrawal symptoms like headaches, fatigue, and irritability when you don’t have your usual amount
  • Coffee no longer gives you the energizing “buzz” it once did

Caffeine sensitivity

While caffeine tolerance occurs from regular use over time, some people are simply extra sensitive to the effects of caffeine. These individuals may feel overstimulated and anxious after just a small amount of caffeine. At higher doses, the overstimulation can be perceived as tiredness.

Caffeine sensitivity can depend on:

  • Genetics – Variations in genes can make you metabolize caffeine slower
  • Age – Older adults are more sensitive to caffeine’s effects
  • Medications – Some medication interactions increase caffeine sensitivity
  • Medical conditions – Conditions like anxiety disorders can increase sensitivity

If you have a low caffeine tolerance, even just one cup of coffee could make you feel jittery and unsettled, eventually leading to sleepiness as you come down from the caffeine high.

Adenosine receptor differences

We know caffeine blocks adenosine receptors to provide an energizing effect. But some people may have differences in their adenosine signaling that causes caffeine to have more of a depressant effect.

Research has found that mice bred to lack a particular type of adenosine receptor (A2A receptors) experienced sedation when given caffeine. Normal mice given caffeine became more active. This suggests variations in adenosine signaling can alter the effects of caffeine.

In humans, differences in adenosine receptor genes may predispose some people to feel sleepy after caffeine intake. More research is still needed to confirm links between adenosine receptor variants and caffeine sensitivity.

Withdrawal effect

For people who consume caffeine regularly, skipping your morning coffee can trigger withdrawal effects. Caffeine withdrawal symptoms like fatigue and low energy are common among those with a physical dependence.

These withdrawal effects can make you feel sleepier than you normally would later in the day after abstaining from caffeine. Once you ingest caffeine again, it will perk you up temporarily by relieving the withdrawal. But then the crash comes after as the caffeine leaves your system again.

This cycle can make it seem like the caffeine is causing sleepiness. When in reality, it is alleviating your caffeine withdrawal, which recurs once the caffeine wears off.

Sugary coffee drinks

Coffee itself does not make you sleepy. But the extra ingredients added to popular coffeehouse drinks like lattes, frappuccinos, and macchiatos can.

These sugary coffee-based drinks often contain:

  • Added sugar
  • Flavored syrups
  • Whipped cream
  • Chocolate
  • Other carbohydrate sources

Consuming carbohydrates triggers your body to produce more insulin. Insulin promotes the uptake of amino acids to muscles, as well as the synthesis of serotonin. Serotonin is a neurotransmitter that has calming effects and can induce sleepiness.

The combination of caffeine and sugar found in many coffee drinks causes an energy spike, and then a crash as insulin levels spike and fall. This can make you feel very sleepy a couple hours after consumption.

Disrupted sleep cycles

Caffeine consumed too late in the day can disrupt your natural sleep cycle. The effects of caffeine can last for 3-5 hours (or even up to 8 hours for some). Coffee consumed in the late afternoon or evening can make it harder to fall asleep at night.

This can reduce total sleep time and quality of sleep. The resulting sleep deprivation the next day causes daytime sleepiness. Since you consumed coffee the day before, it creates an association between coffee and sleepiness.

Timing is important – an afternoon or evening cup of coffee is more likely to cause sleepiness the next day compared to morning coffee.

Dehydration

Caffeine has a mild diuretic effect, meaning it causes fluid loss. Coffee in particular can be dehydrating since caffeine is a diuretic, and coffee also contains diuretic compounds besides caffeine.

Even mild dehydration of 1-2% fluid loss can cause daytime sleepiness and fatigue. If you do not drink enough water to counteract the fluid loss from coffee, you may become dehydrated.

Aim for at least 8 glasses of water per day when consuming coffee regularly to avoid dehydration effects.

Low blood sugar

Caffeine triggers the release of epinephrine (adrenaline), which signals the liver to produce extra glucose. But after this initial blood sugar boost, caffeine can also inhibit insulin release. Insulin helps shuttle glucose from the bloodstream into cells to be used for energy.

Without enough insulin, blood sugar levels can fall. Hypoglycemia, also known as low blood sugar, can cause symptoms like fatigue, dizziness, shakiness, and confusion – which may present as sleepiness after drinking coffee on an empty stomach.

Eating something small with coffee can help maintain more stable blood sugar levels.

Stomach irritation

For some people, coffee is irritating to the stomach lining. This can be due to the acids present in coffee, the temperature, or the caffeine content.

Stomach irritation from coffee can cause indigestion, feelings of nausea, and gut inflammation. Your body has to expend energy responding to this irritation.

When the body’s energy is directed towards digestion, it leaves less available for cognitive focus and wakefulness. This can lead to sleepiness after drinking coffee, especially in those prone to indigestion.

Habit

If you regularly feel sleepy after drinking coffee in the morning or afternoon, it may simply be behavioral habit and conditioning.

Our bodies follow circadian rhythms that dictate times of day when we naturally feel more alert or sleepy. For many people, sleepiness sets in during the mid-afternoon.

If you regularly have a coffee break at that time, your body associates the routine with sleepiness. The act of drinking coffee becomes tied to feelings of sleepiness even if the coffee content itself is providing energy.

Changing the timing of when you have coffee may help break this association.

Table: Summary of why coffee causes sleepiness

Reason Explanation
Caffeine tolerance Regular use builds tolerance so caffeine has less of an energizing effect
Caffeine sensitivity Some people are extra sensitive to caffeine’s effects
Adenosine receptor differences Variations in adenosine signaling may alter caffeine’s effects
Caffeine withdrawal Skipping coffee triggers withdrawal fatigue that caffeine intake relieves temporarily
Sugary coffee drinks Added carbohydrates and sugar cause an energy crash
Disrupted sleep Late day caffeine impairs sleep quality
Dehydration Coffee has a mild diuretic effect that can cause dehydration and fatigue
Low blood sugar Caffeine can inhibit insulin, leading to hypoglycemia
Stomach irritation Coffee irritates the stomach in some people, using energy and causing sleepiness
Habit A conditioned response creates an association between drinking coffee and feeling sleepy

Conclusion

There are many reasons why coffee may be causing sleepiness instead of energy, despite its caffeine content. Understanding the root cause can help you take steps to minimize this effect, so you can enjoy your coffee without the unintended drowsiness.

Pay attention to your caffeine tolerance, timing of intake, sleep habits, hydration, nutrition, and whether coffee upsets your stomach. Adjusting these factors can help optimize your coffee routine for energizing effects.

However, some individuals will always be extra sensitive to caffeine and prone to negative symptoms like jitteriness and sleepiness. If coffee continues to make you feel sleepy no matter what you try, consider lowering your intake or opting for lower-caffeine or decaf varieties. Prioritize getting enough sleep, regular exercise, hydration, and a balanced diet to maintain your energy levels.