“Caffeine intoxication” became official in the medical community when the “Diagnostic and Statistical Manual of Mental Disorders,” known as DSM-5, added the diagnosis last year.

So do cappuccino lovers need to worry about limiting their consumption?

One expert, Matthew Johnson, associate professor in the department of psychiatry at Johns Hopkins University, explains how caffeine works in the body and when to cut back.

Caffeine works by blocking adenosine, a neuromodulator in the brain that puts the brakes on excitatory neurotransmitters like dopamine and norepinephrine. “Caffeine allows these stimulating chemicals to flow, which can have a rousing effect, even at very low doses,” says Dr. Johnson, a psychopharmacologist who studies the influence of drugs on behavior and mood.

Some people will get edgy from a weak cup of tea. For others, a double espresso is required to get them into the shower in the morning.

Most coffee drinkers are familiar with at least some symptoms of overindulging—nervousness, excitement, insomnia, rambling thoughts. But a large majority of people who consume caffeine don’t experience severe consequences, Dr. Johnson says.

Click for more from The Wall Street Journal.