We’ve become a nation of coffee drinkers, downing 500 cups a year. But when we have that first cup of coffee in the morning, many of us also consider it a good time to take our medications — and that’s not always a good thing.
Researchers have found that coffee can affect the way some medications are absorbed, broken down and eliminated from the body, sometimes with serious consequences.
Blood pressure pills
If you are one of the quarter of UK adults who suffer from high blood pressure, you may also want to reconsider taking your blood pressure medication with your morning coffee.
“Caffeine narrows blood vessels (by blocking adenosine receptors, which are responsible for widening them), which can increase blood pressure,” explains Professor Parastou Donyai, chief scientist at the Royal Pharmaceutical Society. “This can work against prescribed high blood pressure medications.”
Britain has become a nation of coffee drinkers: we drink 500 cups a year.
The effect is short-lived, but can also distort blood pressure readings.
Dr Natalie Rout, a GP in London, adds: “I recommend avoiding coffee altogether alongside blood pressure medication. And (if you do drink it), wait an hour or two after drinking coffee before measuring your blood pressure, to ensure an accurate reading.”
Medications for the thyroid
Caffeine increases the contraction of the muscles that move food through the intestine, meaning that medications may move too quickly before they can be absorbed.
This is a problem for people taking levothyroxine, a thyroid hormone medication prescribed to treat an underactive thyroid (hypothyroidism): the medication is absorbed through the barrier cell layer lining the gut.
Taking it with coffee can reduce the amount of levothyroxine absorbed, due to the faster rate at which it passes through the gut. Dr. Rout says, “Take your thyroid medications in the morning on an empty stomach and wait an hour before drinking coffee.”
Taking it at night is also an option: A 2022 study found that levothyroxine was just as effective when taken before bed, hours after eating.
Medications for heartburn
Millions of Britons take omeprazole for indigestion, heartburn and acid reflux, but caffeine negates the drug’s desired effects, says Dr Rout.
Omeprazole is a proton pump inhibitor, which means it stops the cells in the stomach lining from producing too much acid. Reducing the amount of acid in turn reduces the symptoms of acid reflux and may also prevent stomach ulcers.
Caffeine, on the other hand, stimulates the secretion of hydrochloric acid.
‘Take omeprazole on an empty stomach and consider giving up coffee altogether because hopefully then you won’t need to take the medication at all,’ advises Dr Rout.
However, she adds, caffeine may not be the culprit: “Aside from caffeine, there are several things that can make acid reflux worse: tobacco, alcohol, spicy foods, fruit juices and carbonated drinks. Sometimes elimination trials are necessary to determine which factors are causing it.”
Anticoagulants
One medication that people should be especially careful about taking with coffee is the blood thinner warfarin, especially older people.
As Dr. Rout explains: “Each drug is metabolized by the body in a particular way, and many of them are metabolized in the liver by something called the P450 system (enzymes in the body involved in drug metabolism). Drugs either “induce” or “inhibit” the P450 system.
Researchers have found that coffee can affect the way some medications are absorbed, broken down and eliminated from the body, sometimes with serious consequences.
‘Caffeine is also metabolized by the P450 system, so it interacts with certain medications, such as warfarin, causing an increase in the availability of the drug.’
High levels of the anticoagulant mean that the blood takes longer to clot, which increases the risk of bleeding.
“I recommend taking warfarin with water, not coffee, to avoid increasing the risk of bleeding,” says Dr. Rout.
Pills for depression
The P450 process is also a reason you might want to reconsider taking antidepressants like fluvoxamine (a type of selective serotonin reuptake inhibitor, or SSRI) with coffee. (The effect hasn’t been studied in depth with other SSRIs, such as Prozac.)
Fluvoxamine blocks the P450 enzyme, which lengthens the time it takes for the body to eliminate caffeine. The same process can also counteract the desired effects of ADHD medications and cause agitation.
As Professor Donyai explains: “Caffeine is a stimulant (so it speeds up the central nervous system, increasing heart rate and blood pressure), and combining it with stimulant drugs used for ADHD can increase the side effects of the medication,” which include irritability and anxiety.
Supplements
It’s not just prescription medications that people need to be aware of: some over-the-counter medications can also interact with coffee.
Caffeine prevents the release of a compound called antidiuretic hormone, which in turn causes more urine to be produced.
This is because antidiuretic hormone controls the amount of water released by the kidneys. Caffeine prevents the release of this compound, which results in increased urine production.
As a result, important minerals and vitamins, including B vitamins, magnesium and calcium, can be excreted in urine. Coffee can also reduce iron absorption (by forming a compound with it that is insoluble, so the iron cannot be absorbed by the intestine), so doctors recommend taking a break before drinking tea or coffee after taking iron supplements.
Some medications work better with it.
Headaches: Combining the painkillers aspirin and paracetamol with caffeine may make them more effective.
In a 1986 study, scientists in Thailand found that drinking the equivalent of two cups of coffee along with aspirin led to more of the drug being absorbed. And in 2019, researchers in Malaysia found that caffeine interacted through the P450 system to increase paracetamol levels in the body.
Debbie Shipley, director of information and support services at The Migraine Trust, said: ‘Caffeine works by inhibiting an enzyme called cyclooxygenase which mediates inflammation and pain at certain sites and by blocking certain receptors in the brain called adenosine receptors, which may help relieve migraines.’
She adds that it is important to be consistent with caffeine consumption, as it can be a trigger for migraines. Therefore, if you are taking in additional caffeine through painkillers, you should adjust your coffee and tea intake by drinking less.
Combining the painkillers aspirin and paracetamol with caffeine may make them more effective.
Movement disorders: Surprisingly, coffee may reduce dyskinesia, a movement disorder characterized by uncontrollable tremors, tics or jerks, caused as a side effect of levodopa, a Parkinson’s drug.
Studies have shown that the effect can be produced with one and a half cups of coffee a day.
Michael Schwarzschild, professor of neurology at Harvard Medical School, said: ‘Evidence in people and mice shows that caffeine can block the action of brain receptors called adenosine A2A receptors, which may prevent dyskinesia.
‘This means that caffeine may reduce the risk of developing dyskinesia in Parkinson’s if combined with levodopa from the start, but this needs to be tested in a clinical trial.’
Bottom line? “In general, take medications with a glass of water and wait an hour before drinking any caffeinated beverages,” Dr. Rout advises.