Caffeine is a stimulant. This means it can make people feel more awake and alert. Other effects caused by activating the nervous system can include an increase in heart rate and feeling shaky. Caffeine works by blocking the docking station, or receptor, on nerve cells for the chemical Adenosine. Adenosine is a constituent of the energy molecule ATP, which is produced when food is metabolized. One theory of caffeine’s effect is that as we go through the day and burn energy, adenosine builds up and starts to signal that we are tired. Caffeine blocks that effect. However, like other habit-forming chemicals, the body develops dependency to caffeine.

The two components of dependency are tolerance and withdrawal. Because of tolerance, the body needs more and more caffeine to achieve the same effect because it becomes used to the caffeine. On a molecular level, nerve cells (or neurons) start producing more adenosine receptors to account for being blocked by caffeine, so there are more receptors to trigger sleepiness and lowered alertness. Withdrawal occurs when uncomfortable symptoms are caused when the body doesn’t get the regular amount of caffeine it is used to, and the nervous system screams out for it, and is sluggish without it. Caffeine withdrawal symptoms can include fatigue, headaches, irritability and low mood.

People may feel as though their thinking is sluggish. With frequent caffeine consumption, some people who are sensitive to its effects may experience withdrawal symptoms even if they don’t have caffeine at the usual time of day. An example of this is with coffee drinkers who may have their morning cup of coffee later on the weekend than usual. Migraine sufferers are particularly sensitive to those effects. So, the effect of caffeine is similar to other habit-forming compounds — at first the person experiences a positive effect, but then tolerance sets in, requiring the person to consume more and more, creating a steady habit of use, and eventually caffeine doesn’t enhance the way a person feels, but they have to keep consuming it just to not feel worse than usual because of withdrawal.

This is how people can get hooked on coffee. What about the direct, negative psychiatric effects of caffeine? These can include irritability, short-fuse, depression, anxiety, and insomnia. Caffeine can contribute to insomnia when consumed anytime after the early afternoon. Because of the effect of caffeine on anxiety, it has been used to actually trigger Panic Attacks in some studies of this disorder. The general health effects of caffeine is a matter of debate, with some studies suggesting an elevated cardiovascular risk, and others finding a health benefit thought to be related to the antioxidants found in coffee.

Best Regards, Neal G. Ranen, M.D.