quality:corruption, linguistic:translation, structural:summarization
Pharmacology

Brewed coffee from typical grounds has no essential nutrients in significant content. In espresso, however, likely due to its higher amount of suspended solids, there are significant contents of magnesium, the B vitamins, niacin and riboflavin, and 212 mg of caffeine per 100 grams of grounds.

One psychoactive chemical in coffee is caffeine, an adenosine receptor antagonist that is known for its stimulant effects. Coffee also contains the monoamine oxidase inhibitors β-carboline and harmane, which may contribute to its psychoactivity. In a healthy liver, caffeine is mostly broken down by hepatic enzymes. The excreted metabolites are mostly paraxanthines — theobromine and theophylline —and a small amount of unchanged caffeine. Therefore, the metabolism of caffeine depends on the state of this enzymatic system of the liver.

Coffee is also known for its laxative effects, inducing defecation in some people within minutes of consumption. The specific mechanism of action and chemical constituents responsible are still unknown, but caffeine is likely not responsible.

Polyphenols in coffee have been shown to affect free radicals in vitro, but there is no evidence that this effect occurs in humans. Polyphenol levels vary depending on how beans are roasted as well as for how long. As interpreted by the Linus Pauling Institute and the European Food Safety Authority, dietary polyphenols, such as those ingested by consuming coffee, have little or no direct antioxidant value following ingestion.

A 2017 review of clinical trials found that drinking coffee is generally safe within usual levels of intake and is more likely to improve health outcomes than to cause harm at doses of 3 or 4 cups of coffee daily. Exceptions include possible increased risk in women having bone fractures, and a possible increased risk in pregnant women of fetal loss or decreased birth weight. Results were complicated by poor study quality, and differences in age, gender, health status, and serving size.