Revealed: The Commonly Used Tablets That Stop Working When You Take Them With Coffee

We’ve become a nation of coffee drinkers, consuming as many as 500 cups a year. But when we reach for that first cup in the morning, many of us also see it as a good time to take our meds — and that’s not always a good thing.

Researchers have discovered that coffee can affect the way certain medications are absorbed, broken down and removed from the body, sometimes with serious consequences.

Blood pressure pills

If you’re among the quarter of adults in the UK who have high blood pressure, you may also want to consider taking your blood pressure medication alongside your morning coffee.

‘Caffeine narrows blood vessels (by blocking adenosine receptors, which cause them to widen), which can increase blood pressure,’ explains Professor Parastou Donyai, chief scientist at the Royal Pharmaceutical Society. ‘This may work against drugs prescribed for high blood pressure.’

The effect is short-lived, but it can also disrupt blood pressure measurements.

Dr Natalie Rout, a GP in London, adds: ‘I would recommend avoiding coffee completely with blood pressure medication. And (if you do drink it), wait one to two hours after drinking coffee before measuring your blood pressure, to ensure an accurate reading.’

Thyroid medications

Caffeine increases the contraction of the muscles that move food through the intestines, which can cause medications to be absorbed too quickly.

This is a problem for people taking the thyroid hormone drug levothyroxine, which is prescribed to treat an underactive thyroid (hypothyroidism), because the drug is absorbed through the layer of barrier cells that line the gut wall.

Taking it with coffee can reduce the amount of levothyroxine that is absorbed, due to the increased speed at which it passes through the intestines. Dr. Rout says, “Take your thyroid medication 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 at bedtime, hours after eating.

Medication for heartburn

Millions of Britons take omeprazole for indigestion, heartburn and acid reflux, but caffeine cancels out the desired effects of the medication, says Dr Rout.

Omeprazole is a proton pump inhibitor, which means that it stops cells in the stomach lining from producing too much acid. Reducing the amount of acid in turn reduces acid reflux symptoms and can also prevent stomach ulcers.

Caffeine, on the other hand, stimulates the secretion of hydrochloric acid.

‘Take omeprazole on an empty stomach and consider cutting out coffee altogether. Hopefully, you will then not need to take any medication at all,’ Dr. Rout advises.

However, she adds that caffeine may not be the culprit: “Several things besides caffeine can aggravate acid reflux: smoking, alcohol, spicy foods, fruit juices, and sodas. Sometimes it takes a process of elimination to determine what the causative factors are.”

Blood thinners

One drug that people should be extra careful about when taking coffee is the blood-thinning drug warfarin, especially in older people.

As Dr. Rout explains, “Every drug is metabolized in the body in some way, and many 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 discovered that coffee can affect the way some medications are absorbed, broken down and removed from the body, sometimes with serious consequences

‘Caffeine is also metabolized by the P450 system and therefore interacts with certain drugs, such as warfarin, increasing the availability of the drug.’

A higher concentration of blood thinners means that it takes longer for the blood to clot, increasing the risk of bleeding.

“I recommend taking warfarin with water, not with coffee, to increase the risk of bleeding,” says Dr. Rout.

Depression pills

The P450 process is also why you might want to reconsider taking antidepressants like fluvoxamine (a type of selective serotonin reuptake inhibitor, or SSRI) with your coffee. (The effect hasn’t been well studied with other SSRIs, such as Prozac.)

Fluvoxamine blocks the P450 enzyme, which increases the time it takes for caffeine to be cleared from the body. The same process can also counteract the desired effects of ADHD medications and lead to agitation.

Professor Donyai explains: ‘Caffeine is a stimulant (so it speeds up the central nervous system, increasing your heart rate and blood pressure). If you combine it with stimulant medications used for ADHD, the side effects of the medication can be increased.’ These include irritability and anxiety.

Supplements

People should not only think about prescription drugs. Some over-the-counter medications can also interact with coffee.

Caffeine prevents the release of a substance called antidiuretic hormone, which in turn causes more urine to be produced.

This is because antidiuretic hormone regulates the amount of water released by the kidneys. Caffeine prevents the release of this compound, resulting in increased urine production.

This can cause important minerals and vitamins, including B vitamins, magnesium, and calcium, to be excreted in the urine. Coffee can also reduce the absorption of iron (by forming a compound with it that is insoluble, preventing iron from being absorbed from the intestines) — which is why doctors recommend taking a break from tea or coffee after taking iron supplements.

Some medications work better with it

Headache: Combining the painkillers aspirin and paracetamol with caffeine can make them more effective.

In a 1986 study, scientists in Thailand found that drinking the equivalent of two cups of coffee with aspirin led to greater absorption of the drug. And in 2019, researchers in Malaysia found that caffeine interacted with the P450 system to increase the amount of acetaminophen in the body.

Debbie Shipley, head of information and support services at The Migraine Trust, said: ‘Caffeine works by blocking an enzyme called cyclo-oxygenase, which causes inflammation and pain in certain areas. It also blocks certain receptors in the brain called adenosine receptors, which can help relieve migraines.’

She adds that it’s important to be consistent with your caffeine intake, as caffeine can be a migraine trigger. So if you’re taking extra caffeine with your painkillers, you should adjust your coffee and tea intake by drinking less.

Combining the painkillers aspirin and paracetamol with caffeine can make them more effective

Movement disorders: Surprisingly, coffee can reduce dyskinesia. Dyskinesia is a movement disorder characterized by uncontrolled tremors, tics, or shaking. This disorder is a side effect of the Parkinson’s drug levodopa.

Research has shown that the effect is already noticeable when drinking one and a half cups of coffee a day.

Michael Schwarzschild, a professor of neurology at Harvard Medical School, said: ‘Evidence in humans and mice shows that caffeine can block the action of brain receptors called adenosine A2A receptors, which can prevent dyskinesia.

‘This means that caffeine may reduce the risk of developing dyskinesia in Parkinson’s disease if combined with levodopa from the start. However, this still needs to be tested in a clinical trial.’

The bottom line? “In general, take medications with a glass of water and wait an hour before consuming caffeinated beverages,” Dr. Rout advises.