Have you been drinking coffee for years and are starting to feel weird sensations after a cuppa?
You’ve got to know something.
If you suddenly find yourself going through unusual post-caffeine effects such as anxiety, headache, faster heartbeat and tremors, you may be experiencing a shift in how your body metabolizes caffeine.
Two words: caffeine sensitivity.
According to Caffeine Informer: 
Caffeine sensitivity is determined by the efficiency of the human body to process and metabolize caffeine.
This shouldn’t be confused with caffeine tolerance, which describes how the body responds to caffeine over time.
Caffeine sensitivity is not necessarily a bad thing. Sometimes, it’s all a matter of our body adapting to caffeine in our system.
However, if all of a sudden you start to feel things that didn’t used to happen after having your java fix, then it’s time to watch that caffeine intake!
There are three kinds of caffeine consumers - those who experience intense reactions to it at minimal amount, those who can go overboard because having way too much doesn’t really affect them, and those who are somewhere in the middle.
In scientific terms, people are divided according to three levels of caffeine sensitivity:
This is where the majority of the people fall under. With normal sensitivity, they can consume up to 400 milligrams of caffeine in a day and not experience anything unpleasant. 
(Related article: Here’s how much caffeine you should have in a day)
If you normally consume caffeine in the morning and can go on the day without feeling any of caffeine’s bad rap, i.e. jitters, palpitations, anxiety, then you’re part of this group!
A 2011 study identifies 10 percent of the entire population to be hyposensitive. They have the ability to consume caffeine at a higher-than-normal dosage and not experience any adverse effects. 
If you find yourself drinking coffee until late afternoon - or even at night - and still hit the hay without any difficulty, then consider yourself hyposensitive to caffeine.
Those who fall under this category experience amplified effects of caffeine even at a small dosage, say 100 mg.
If you notice that you go through negative effects like a headache, insomnia, tremors, and palpitations with a few sips of tea or coffee, then your body must be taking longer to metabolize caffeine.
Caffeine sensitivity is not a random phenomenon that can just happen to any coffee-lover like you. There are a number of factors why you respond to caffeine the way you do:
Certain medications react to caffeine differently. The medicine you take may either amplify or diminish its effects on your body. If you want to find out which medicines have reactions to caffeine, you may check out this article, “Caffeine and medication: can you combine them?”
The body’s ability to metabolize caffeine depends on your genetic makeup:
Because caffeine binds to adenosine receptors, its effects depend on the type of receptors found in your brain (correct ones should exist to get the most of your caffeine fix). 
Caffeine sensitivity becomes more likely when a woman takes oral contraception or becomes pregnant. This is because of higher estrogen levels, which hampers CYP1A2 from fully functioning.
According to "Is caffeine safe during pregnancy?"
Having a bun in the oven slows down the body’s ability to break down caffeine, so higher levels of caffeine stay longer in the bloodstream. The farther along you are, the longer caffeine stays in your system, and the more intense its effects are in your body. 
While not necessarily detrimental, caffeine sensitivity may bring about inconvenience and discomfort.
•feelings of jitteriness and unease
• anxiety or nervousness
•trouble sleeping or insomnia
• upset stomach
•elevated heartbeat or blood pressure
•involuntary muscle spasms
The most logical - albeit not the easiest - way to get rid of caffeine sensitivity is to take it easy on your caffeine fix. It makes total sense to try easing off on your go-to caffeine (or rid it altogether if you can).
Be extra cautious on your caffeine intake. It doesn't hurt if you'd start reading the label more and monitor your caffeine mg's. Find out up to what amount of caffeine your body can take and stick to it.
Veer away from highly caffeinated products. Try switching to decaf or have some black or green tea instead.
You may find more tips on laying low on caffeine in the article, "Caffeine withdrawal symptoms and how to reduce them."
Ask yourself this existential question - why do I still drink coffee?
But humor aside, since you don't necessarily get the positive effects of caffeine (you seem to be immune in it anyway), assess whether you still get any advantage from getting caffeinated. Otherwise, you may as well switch to decaf so you can steer clear of the adverse effects of consuming caffeine over a long period. 
Just always remember the acceptable amount of caffeine and don't go overboard. Here's how much caffeine you should have in a day.
You can also check how much caffeine is in your favorite brand of coffee here.
What kind of caffeine sensitivity do you think you have? Got any tips on how to overcome it? Leave them in the comments section below!
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Considered as supplements, these are your caffeine fix taken in capsule form. They may have natural caffeine straight from the brewing process, while others may have synthetic or artificial caffeine.
Caffeine pills provide the same stimulating benefits as coffee and other caffeine beverages.
Note that caffeine pills aren’t exactly those caffeine powder you see in bulk from the retail stores. In fact, the US Food and Drug Administration or FDA considers caffeine powder as “potentially dangerous.”  Caffeine pills are generally safe, though there are some precautions to note, which we’ll talk about later.
If you’re trying to lose weight (or at least not gain a few extra pounds), then the best thing to do is eat healthy and go to the gym more religiously, right?
But if you’ve been going at it for a while now and haven’t been seeing much progress, then you may want to look into something else.
Like your coffee consumption.
Now you may ask: what does an innocent cup of joe have to do with weight gain?
Let me tell you.
It’s not as innocent as it seem.
That cup of coffee you buy on your way to work? It may be sneaking in a few extra calories (more than you’d like and expect). And if you buy more than one cup a day, you may be racking up a few calories from a “dessert” that disguises itself as your go-to caffeine fix.
The holidays are upon us. It’s only October but with the rate this year has gotten to the tail-end, we’ll all be wearing our favorite sweatshirts (forcibly or otherwise) and devouring the holiday away in no time.
The forward-looking you will already be starting to watch that *extra holiday weight* before the holiday even starts.
But one step at a time, right? After all, there’s a few weeks left before the celebrations and holiday parties officially kick in.
If the java lover in you has ever been curious whether caffeine can help curb the appetite, now is the perfect time to find some answers.
The word on the street is that caffeine is one of the best appetite suppressants.
Spoiler alert: researches tell us the jury’s still out on this one.