Got to have that morning rush, whether it is from coffee, tea, chocolate, soft drinks, energy drinks or some other form of caffeine?

You are not alone. In North America 90% of adults use caffeine. It is the most widely consumed psychoactive drug, yet it is legal and largely unregulated.

Caffeine acts on the brain through several metabolic mechanisms. Most important is to counteract adeno­sine, a neurotransmitter that suppresses activity in the central nervous system.

Because caffeine blocks adenosine receptors, it also affects most of the other major neurotransmitters, including dopamine, acetyl­choline, serotonin and, in high doses, norepinephrine and gamma-aminobutyric acid. To a small extent it affects epinephrine, glutamate and cortisol.

There are both positive and negative aspects to caffeine. For example, it stimulates the brain’s pleasure centers, but it is mildly addictive. It can lead to complications in pregnancy when consumed in large amounts, but it might provide protection against Parkinson’s and some cancers.

The relatively small amounts consumed by most people have low health risks even over long-term use. Every person responds differently to caffeine, which makes it difficult to make general statements about health risks.

A growing caffeine food industry has caused the Food and Drug Administration to scrutinize the amount of caffeine in food products.

As of July 2013 the agency has restricted beverages to containing less than 0.02% caffeine. The FDA also said that less than 400 milligrams per day does not generally have dangerous negative effects, and it considers 1,000 mg the borderline for toxicity.

This recent regulation arose because manufacturers have begun to put large doses in larger serving sizes. The FDA is concerned about the cumulative effects of intake throughout the day, which the agency fears could lead to strong dependency. Furthermore, consumption by children may be linked to neurological and cardiovascular problems.

There have been at least seven deaths from caffeine since 2009. Compared with other substances such as acetaminophen (the active ingredient in Tylenol), the death rate is small, but the fact that it has caused deaths raises a red flag.

In October 2013 a man in the U.K. died after eating a tin of 12 chocolate mints, each one of which contained 80mg of caffeine — nearly as much as a can of Red Bull. The tragedy occurred despite a warning on the package to not eat more than five mints in a 24-hour period.

Coffee contains the highest amount of caffeine of any natural beverage. A 20-ounce Starbucks beverage can contain over 400 mg, equivalent to two shots of 5-hour Energy.

There is growing concern among health professionals that manufacturers are deliberately spiking high concentrations in their products specifically to rely on the addictive qualities of caffeine in children’s drinks in order to recruit long-term users of their products.

Caffeine is not the only player in the energy drink business. Other additives such as taurine, niacin, L-carnitine and pyridoxine have been implicated in deaths from energy drinks. In concert with alcohol or heart disease, the lethal amount is reduced for anyone.

This is by far not the complete story of caffeine. It has been extensively studied, and because it is so ubiquitous, the studies continue.