Within the first 30-45 minutes after waking, your cortisol levels naturally increase sharply (Clow, 2010), typically reaching their highest levels early in the morning — typically between 6 a.m. and 9 a.m. This surge, often called the “cortisol awakening response,” is designed to help you wake up and feel alert. Unfortunately, this happens to be the exact time most of us reach for that first (or second and third) cup of coffee.

Caffeine’s relationship with cortisol is complex—it’s not just about waking you up; it directly affects how your body responds to stress. Here’s how caffeine interacts with your stress hormones and how your coffee habit can be affecting your cortisol levels.

1. Caffeine Blocks Adenosine, Your Brain’s “Sleep Signal”

Caffeine’s primary job is to block adenosine, the brain chemical that promotes relaxation and drowsiness. By doing this, you feel more alert and focused. However, this same blockade signals your body to produce adrenaline and cortisol — both of which are tied to the body’s “fight or flight” response. In other words, caffeine isn’t just telling you to wake up; it can make your body scream, “danger!”.

Essentially, caffeine is hijacking a system evolved over thousands of years to help us survive life-or-death situations, like outrunning a predator on the savannah. But instead of fleeing from lions, we’re now sitting at desks, staring at laptops, and stressing over deadlines—proof that our biological wiring isn’t always the best fit for our modern lives.

2. Caffeine Can Spike Cortisol Levels

Numerous studies indicate that caffeine consumption can lead to a cortisol spike, even in daily coffee drinkers (Cole, 2024; Lovallo, 2005; Lovallo, 2006). While regular coffee drinkers may develop some tolerance over time, factors like stress, lack of sleep, and dehydration can amplify the effect.

For example, if you exceed your usual amount of caffeine on a particularly hectic day, you might experience an even bigger surge in cortisol—and the accompanying jitters, anxiety, and wired feeling. This is why that extra cup of coffee during a stressful workweek might leave you feeling more frazzled and less focused while a cup of coffee on a calm weekend morning has no negative effects.

3. The Domino Effect on Blood Sugar and Energy

Caffeine doesn’t just affect cortisol and perceived stress levels—it can also lead to a short-term spike in blood sugar by decreasing insulin sensitivity (Shi, 2016; van Dam, 2004). In simpler terms, caffeine makes it harder for your body to process sugar efficiently, which can contribute to the energy crash you may feel later in the day.

If you’ve ever experienced a “coffee crash” a few hours after drinking coffee, this cortisol-blood sugar connection might be to blame. It’s a double whammy: caffeine gives you a quick boost, but the resulting cortisol spike and blood sugar imbalance can leave you feeling even more drained than before.

Now that we’ve explored how caffeine affects cortisol, let’s look at why timing matters—especially first thing in the morning—and how a few strategic tweaks to your routine can help you maintain steady energy levels all day long.