Lithium and diuretics: why water tablets need care

The NHS describes lithium as a mood stabiliser used for mood disorders such as mania, hypomania, repeated episodes of depression where other treatment has not worked, and bipolar disorder. It also says lithium can help reduce aggressive or self-harming behaviour. It comes as regular or slow-release tablets and as a liquid.

Lithium is unusual because the level in the blood is checked regularly. The NHS says you will have blood tests to see how much lithium is in your blood, and your results are recorded in your lithium record book. You are also given an alert card to keep with you at all times, which tells health professionals in an emergency that you take lithium. Both exist because small changes in how the body handles lithium can matter.

Diuretics, often called water tablets, make you pee more. The NHS describes furosemide as used to treat a build-up of fluid in the body, often caused by heart failure, chronic kidney disease or severe liver damage, and says it can also be used for high blood pressure. Bendroflumethiazide is described as used to treat high blood pressure and a build-up of fluid. Its side effects, the NHS says, include needing to pee more often, dehydration, and low or high levels of salts such as potassium or sodium in your blood.

The NHS lithium page says that some medicines may affect the way lithium works and this can change the levels of lithium in your blood. It lists diuretics such as furosemide or bendroflumethiazide first among the examples. The furosemide page lists lithium in the group of medicines that may not mix well with it. Both pages ask you to speak to your doctor or pharmacist about them.

The pages read for this guide do not explain the mechanism in detail, so this guide does not either. The practical thread running through the NHS advice is that lithium levels are sensitive to salt and fluid balance, and diuretics change both.

The NHS lithium side effects page says that although it is rare, having too much lithium in the blood can cause problems with the kidneys and other organs. It says to call 999 or go to A&E now if you have any of these symptoms, which it calls signs of lithium toxicity, and that you should stop taking lithium straight away:

• Stomach ache, feeling sick and diarrhoea.

• Problems with eyesight, such as blurred vision.

• Feeling very thirsty, needing to pee more than normal, and lack of control over pee or poo.

• Feeling light-headed or drowsy, confusion and blackouts.

• Shaking, muscle weakness, muscle twitches, jerks or spasms affecting the face, tongue, eyes or neck.

• Difficulty speaking.

The NHS gives practical steps. Go to the blood tests arranged by your doctor. Do not reduce your salt intake suddenly, and talk to your doctor if you want to cut salt. Drink plenty of fluids, especially if you are doing intense exercise or in hot weather when you sweat more. Alcohol makes the body lose water, so the NHS says it is best not to drink too much. Always tell any doctor or pharmacist that you take lithium before taking a new medicine.

Illness is another moment to take care. The NHS lithium side effects page advises sips of water if you are being sick, to avoid dehydration, and says to drink plenty of fluids with diarrhoea. The bendroflumethiazide page says that if you have diarrhoea or vomiting from a stomach bug or other illness, you may need to stop taking it for a short time. Ask the prescriber or pharmacist what to do with each of your medicines on a sick day, and do this before it happens, not during.

The NHS lithium page lists several groups besides diuretics: non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, celecoxib or diclofenac; ACE inhibitors such as enalapril, lisinopril or ramipril; some antidepressants such as fluvoxamine, paroxetine or fluoxetine; antibiotics such as oxytetracycline, metronidazole, co-trimoxazole or trimethoprim; and epilepsy medicines such as carbamazepine or phenytoin. It stresses that these are not all the medicines that can affect lithium.

There is also a caution about herbal remedies. The NHS says there is not enough information to say that complementary medicines, herbal remedies and supplements are safe to take with lithium, because they are not tested in the same way as pharmacy and prescription medicines.

For people who take a diuretic and an ACE inhibitor as well as lithium, which is a fairly common combination in older adults with heart or kidney problems, the number of items on the list adds up quickly. A medicines review with a pharmacist or the prescriber is the place to sort this out.

The NHS says taking lithium for a long time can cause problems with the kidneys or thyroid gland, and that the doctor will arrange blood tests to check for changes. It lists signs of an underactive thyroid, such as tiredness, weight gain and feeling depressed, and signs of kidney problems, such as swollen hands or ankles, feeling tired and short of breath, changes in pee and feeling sick. Because diuretics are also processed by the kidneys, the same blood tests help to watch the combination.

On the NHS, lithium monitoring is usually shared between mental health services and the GP surgery, with the lithium record book and alert card as the common reference. Community pharmacists can check over-the-counter products against lithium. A private psychiatrist may also arrange blood tests and prescriptions, but the same principles apply: whoever prescribes a new medicine or diuretic needs to know you take lithium, and results should reach the clinician who is responsible for your lithium.