Coffee Interactions

Coffee (and orange juice) sharply reduce the absorption of alendronate, an oral bisphosphonate whose baseline absorption is already very low. Taking the tablet with coffee instead of plain water can cut the absorbed amount enough to make the dose ineffective for protecting bone.

Coffee can reduce how much levothyroxine you absorb when the two are taken at the same time. Chlorogenic acids and other compounds in coffee appear to bind the hormone in the gut, and coffee can also speed gastric transit, leaving less time for the tablet to dissolve. The effect largely disappears when the dose and the coffee are separated by enough time.

Caffeine in coffee acutely raises heart rate and blood pressure, which can partly counteract the heart-rate and blood-pressure-lowering effects of propranolol, a non-selective beta-blocker. Propranolol does not fully block this caffeine pressor response. Older claims that propranolol slows caffeine clearance appear to be wrong: a human study found propranolol slightly speeds caffeine elimination rather than slowing it.

Coffee contains chlorogenic acid and other polyphenols with galloyl groups that bind non-heme iron in the gut, forming poorly soluble complexes the intestine cannot absorb. Drinking coffee with or shortly after an iron-rich meal or supplement meaningfully reduces how much non-heme iron you take up.

Ciprofloxacin inhibits CYP1A2, the liver enzyme that clears caffeine, slowing caffeine metabolism so a normal amount of coffee produces higher, longer-lasting caffeine levels and stronger stimulant effects.

Some antidepressants slow how fast the body clears caffeine by inhibiting the liver enzyme CYP1A2 — fluvoxamine does this most strongly, while fluoxetine, sertraline, paroxetine, and duloxetine have milder effects. At the same time, caffeine independently worsens anxiety, insomnia, tremor, and a racing heart, the very symptoms antidepressants are often prescribed to relieve. With MAOIs, very high caffeine intake has been linked in case reports to blood pressure spikes.

Sertraline is a weak inhibitor of CYP1A2, the enzyme that clears caffeine, so it can slow caffeine metabolism mildly. More relevant in practice, caffeine can add to the jitteriness, palpitations, anxiety, and insomnia that often appear in the first weeks of sertraline. The pharmacokinetic effect is far smaller than with fluvoxamine and is usually minor.

Coffee and tea were historically labeled antithiamine beverages, but later biochemistry walked the claim back: chlorogenic and caffeic acids do not destroy thiamine under physiological conditions, and the real activity comes from polyphenol oxidation products and tannins, which are lower in coffee than tea. The net effect on thiamine status is modest and unlikely to matter for well-nourished people; it becomes relevant only on a marginal diet or in groups already prone to deficiency.