Is the supposed "decaf" from your regular coffee joint keeping you up at night? Or is the expresso double shot not giving you the caffeine hit you hoped for?
One day, you might be able to find out why simply by shining a light into your cup.
Researchers from the National University of Singapore (NUS) have developed a fluorescent compound that will change colour to reveal the amount of caffeine in your drink. Shining a laser pointer into a drink sample will show you red-orange for high levels, yellow for medium and green for low.
This quirky bit of science could prove useful for those with caffeine allergies, or those trying to avoid the stimulant for health reasons, said lead researcher Chang Young-Tae.
Medical studies have found that high caffeine consumption can have both good and bad effects. The addictive drug might lower the risk of diabetes, but could raise blood pressure.
Professor Chang likened his team's discovery, published last month in online journal Scientific Reports, to a traffic light. A reddish-orange colour would be a "stop sign" for people who cannot take caffeine, yellow would provide a "warning signal" and green would indicate a "safe zone".
First water, baking soda and ethanol are added to a drink sample to extract the caffeine. Then, the fluorescent compound called Bodipy is added, after which a laser pointer is used to reveal the caffeine level.
The entire process takes just a minute - current techniques using chromatography to separate and analyse mixtures need up to 20 minutes.
Tests performed by researchers found that gourmet coffee from a well-known cafe chain contained significantly more caffeine than typical energy drinks. A popular brand of soft drink contained only slightly more caffeine than decaffeinated coffee.
Researchers hope to attract interest from the industry to develop a quick test kit that consumers can use to check their regular cup of joe or drinks they pick up at a convenience store.
Such applications might sound trivial to some, but Prof Chang was quick to point out that fluorescent compounds could have many other life-changing uses.
Another compound he has synthesised lights up when a potent "date-rape" drug is detected. A third could in future test for Alzheimer's disease.
Prof Chang's team has amassed a collection of more than 10,000 such compounds for tests, a library which, he said, is the largest in the world.