Brits taking a certain medication are reminded to stick to a 4pm rule. Failing to stick to this advice could keep you up at night.

Bumetanide is a type of medication called a diuretic, designed to make your kidneys produce more urine to help your body get rid of excess salt and water. In the UK, it is prescribed to treat heart failure, which affects almost one million people.

Bumetanide is only available on prescription. It comes as tablets and as a liquid that you swallow.

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Bumetanide also comes mixed with another diuretic called amiloride to treat oedema. However, as is the case with any medication, there are rules about how it should be taken.

On the NHS website, it offers several important guidelines to consider when taking bumetanide. This includes one rule about timings.

According to the NHS, you should not take bumetanide after 4pm as this could mean you need to get up in the night.

It said: “Do not take bumetanide after 4pm or you may have to wake up in the night to go to the toilet.” On top of this advice, there are other recommendations about when to take it and what you should eat.

“You'll usually take bumetanide once a day, in the morning or afternoon – or twice a day, in the morning and afternoon,” the NHS said. “Most people need to pee about 30 minutes after taking bumetanide, and again within a few hours.

“Avoid foods that have a lot of salt in them (processed foods or ready-meals), and the salt substitute, Lo Salt. It can affect how your medicine works.” But the NHS added: “You can take bumetanide with or without food.”

Some people should also be especially careful when taking bumetanide. The NHS said that to make sure that it's safe for you, tell your doctor if you have:

• Ever had an allergic reaction to bumetanide or any other medicines


• Low blood pressure (hypotension)


• Symptoms of dehydration, such as being thirsty, having a dry mouth and dark pee


• Liver disease


• Diabetes


• Difficulty peeing


• Gout

If you're going to have a glucose test, you should also tell your doctor you are taking bumetanide.

There are also some common side effects of bumetanide that happen in “more than” one in 100 people. There are things you can do to help cope with them:

• Peeing more than normal


• Feeling thirsty


• Dry mouth


• Headaches


• Feeling confused or dizzy


• Muscle cramps or weak muscles

You should speak to a doctor or pharmacist if the advice on how to cope does not help and a side effect is still bothering you or lasts more than a few days.

Serious side effects are rare, the NHS said. You should call your doctor or call 111 now if you have:

• Unexplained bruising or bleeding, a high temperature, sore throat and mouth ulcers – these could be signs of a blood disorder


• Ringing in your ears (tinnitus) or loss of hearing

The NHS added: “In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to bumetanide.” In 2023 the UK experienced a national shortage of bumetanide that was expected to resolve in 2025.

As a result, many patients were switched to furosemide, which is also affected by the 4pm guidance.