Thiazides are medications that are used to treat high blood pressure or to reduce fluid retention in cases of oedema.

  1. Treat high blood pressure and fluid retention.
  2. Can be used in combination with other medications.
  3. May also be referred to as diuretics or water pills.

If you have any concerns relating to the conditions described above, you can speak with one of our GPhC-registered clinicians via our online video consultation service. They are available for appointments between 9.30am-4.30pm, Monday to Friday.

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Product information

What are thiazides?

Thiazides belong to a group of medications called diuretics, sometimes referred to as water pills. They are available as tablets or as a liquid suspension and are generally well tolerated, and do not require a prescription. 

They are primarily prescribed to treat hypertension (high blood pressure) either independently or in combination with other medications, but they may also be used to reduce fluid retention in instances of oedema, including cases relating to the body’s major organs. They work by helping the body to flush excess fluid and salt from the system, making it easier for blood to flow more freely through the blood vessels and reducing the swelling and discomfort associated with oedema.

What is hypertension?

Hypertension is a very common condition in the UK, affecting approximately one third of adults. It rarely presents with any symptoms and many people are not aware that they have it. If it’s left untreated, however, it can lead to serious health events, including heart attacks, strokes, heart disease, heart failure, vascular dementia, kidney disease, aortic aneurysms and peripheral arterial disease. The only way of establishing if you have high blood pressure or not is to get your blood pressure checked.  

Blood pressure is measured using two numbers: systolic pressure (the force that the heart pumps blood around the body) and diastolic pressure (the resistance that this force meets in the blood vessels). High blood pressure is diagnosed when these numbers exceed 140/90mmHg (millimetres of mercury). If you are over the age of 80, this increases to 150/90mmHg. Ideal blood pressure is thought to be between 90/60mmHg and 120/80mmHg.  

You can get your blood pressure checked at your doctor’s surgery and many pharmacies. Some workplaces may also provide tests as a matter of course. You can also check your blood pressure yourself using a home test kit. 

What causes hypertension?

Causes of hypertension vary, and in many cases there seems to be no specific trigger. There are however some factors that significantly increase the risk of it presenting, such as poor diet, a lack of exercise, age (the older you are, the more likely it will occur), excessive alcohol consumption, poor sleep, obesity, excessive salt intake, consumption of large quantities of alcohol and a family history of the condition. Having an African or Caribbean background also increases your risk of developing high blood pressure.

How is hypertension treated? 

Making changes to your lifestyle can be effective in many cases, and may mean that you do not need to take medication to reduce your blood pressure. This includes cutting down your intake of salt and eating more fruit and vegetables. Reducing alcohol and caffeine may also provide significant benefits, as well as quitting smoking. 

In the event that you do require medication to control your blood pressure levels, you will likely be given an ACE inhibitor, or an angiotensin-2 receptor blocker (ARB) if an ACE inhibitor is unsuitable for you. 

If you are over 55 years of age or of an African or Caribbean background, you may be offered calcium blockers. Diuretics such as thiazides tend to be prescribed when calcium channel blockers are not well tolerated, but they can be used alongside other treatments in some cases.

What is oedema? 

Oedema can develop anywhere in the body, but it typically presents in the legs, ankles and feet. It’s a build-up of fluid in these areas that is usually caused by the consumption of too much salt, standing for prolonged periods of time, pregnancy, obesity and certain medications (antidepressants, other hypertension medications, the contraceptive pill and steroids). 

Although less common, it may also be caused by blood clots, insect bites or stings, injury, infection or liver or heart and kidney problems. 

Oedema tends to go away on its own after a few days, but if it doesn’t, you should see your doctor to rule out the possibility of something more serious causing the issues. This is particularly important if the swelling only occurs on one leg, ankle or foot (when no injury has happened), you have a fever, you have diabetes, the area affected is hot to the touch, the swelling is particularly bad or if it presents as sudden pain.

How is oedema treated? 

You can treat the symptoms of oedema by avoiding standing for long periods of time and wearing loose fitting clothing until the swelling subsides. Ensuring that your feet are dry at all times can also help avoid infections.

If these practices do not produce the desired results, your doctor may prescribe a diuretic to flush the excess fluid from your system.

If you would like to discuss thiazides or any related conditions, you can book an appointment with one of our registered clinicians for our online video consultation service. They are available from 9.30am-4.30pm, five days a week. Our clinicians can also issue fit notes and referral to specialists for treatment, where appropriate.  

Page last reviewed:  23/07/2020
Side effects and warnings

What side effects can thiazides cause?

All medications carry some risk of side effects. In most cases, thiazides are well tolerated, and produce few issues, particularly when taken at lower dosages. Nonetheless, it is important to be aware of any potential side effects, no matter how rare they are. Your prescribing clinician can advise you about side effects, and you can also refer to the patient information leaflet that comes with your medication for more information. 

Because there are different types of thiazides available, the information below may not be relevant for your specific treatment. The following information relates to the medication bendroflumethiazide.

If you experience any of the following symptoms, discontinue use and seek immediate medical attention: sudden and severe stomach pain, yellowing skin or eyes, dark urine or pale faeces, extreme thirst, dizziness or you are urinating less than four times a day.

You should contact your prescribing clinician immediately if you experience any of the following: 

Allergic reaction (unknown frequency) that includes: rashes including skin that is red, flaky and peeling (exfoliative dermatitis), sensitivity to sunlight or sunbeds, viral infections in the lungs (pneumonitis), fluid in the lungs (pulmonary oedema). 

Blood (up to 1 in 1,000 people): altered numbers and types of blood cells. If you notice increased bruising, nosebleeds, sore throats, recurring infections, extreme fatigue, loss of breath when exerting yourself and abnormal paleness of the skin, you should inform your doctor, who may decide to conduct a blood test. 

The following side effects have been reported but their frequency is not known:

Metabolism: bendroflumethiazide may occasionally affect blood sugar levels (if you are an insulin-dependent diabetic, you insulin dosages may need to be adjusted as your body’s ability to manage insulin may be impacted); An increase in uric acid in your blood that may cause gout. 

Chemicals within the body: (shown in blood tests): low blood potassium levels (hypokalaemia) (which may cause an increase in the frequency and amount of urination, general discomfort and illness, muscle weakness or cramp, dizziness, feeling or being sick and loss of appetite, low blood magnesium and sodium levels, high levels of calcium in the blood (hypercalcaemia), low blood levels of chloride ions with increased alkalinity in the body (hypochloraemic alkalosis).

Stomach and intestines: feeling or being sick, diarrhoea, constipation, stomach irritation 

Other: inflammation of the pancreas; blocked bile flow within the liver (which may present as jaundice, yellowing of the skin or whites of the eyes, dark urine and pale stools); an inability to maintain an erection; dizziness when standing up due to low blood pressure; dizziness. 

Can thiazides cause interactions with other medications? 

All medications can interact with other substances, including other drugs, supplements and even food and drink. You should tell your doctor about any medications you are currently taking, or have recently taken, before starting treatment. You can also refer to the patient information leaflet that comes with your treatment for more information about interactions with other treatments. 

The information below relates to the medication bendroflumethiazide.

Your doctor may consider this treatment unsuitable if you have recently or are currently taking the following: Allopurinol, colestyramine, colestipol, disopyramide, amiodarone, flecainide, quinidine, lidocaine, mexiletine, tricyclic antidepressants, reboxetine, monoamine-oxidase inhibitors (MAOIs), sulfonylureas, carbamazepine, amphotericin, prazosin, ACE inhibitors, angiotensin-II antagonists, pimozide, thioridazine, calcium salts, calcium channel blockers, moxisylyte, corticosteroids, digoxin, aminoglutethimide, toremifene, lithium, baclofen, tizanidine, tubocurarine, gallamine, alcuronium, pancuronium, indometacin, ketorolac, ibuprofen, piroxicam, naproxen, oestrogens, combined oral contraceptives, sympathomimetics, theophylline, carbenoxolone and vitamin D. 

Warnings and precautions when taking thiazides 

You should make your prescribing clinician aware of any health conditions you have or are prone to before starting treatment with thiazides. 

It’s particularly important that you tell them about any of the following conditions: allergies to Bendroflumethiazide tablets, thiazides in general or to any ingredients of this medicine, severely impaired kidney function, severely impaired liver function, high levels of calcium in the blood, low levels of sodium in the blood, low levels of potassium in the blood, gout and Addison’s disease. 

Your doctor may need to consider an alternative treatment if you have any of the following: moderately impaired kidney, moderately imparied liver function, alcoholic cirrhosis of the liver, diabetes, systemic lupus erythematosus (SLE) or porphyria.

Is it safe to take thiazides if you are pregnant? 

If you are planning on becoming pregnant, think you might be pregnant, are pregnant or are currently breastfeeding, you should not use these treatments. Your doctor may be able to find another suitable medication in these circumstances. 

What types of thiazides are available? 

Thiazides are usually available in one of two forms: tablets or liquids, which are taken orally.

In the UK, the most common products available include: Bendroflumethiazide and cyclopenthiazide (Navidrex), chlortalidone (Hygroton), indapamide (Natrilix) and xipamide (Diurexan).

Page last reviewed:  23/07/2020
Questions and Answers

Can thiazides affect your ability to drive? 

Some thiazides may produce side effects that will affect your ability to operate heavy machinery, including dizziness and blurred vision. While the risks are small, you should be aware of them before starting treatment and avoid driving if you experience them. 

Can I consume alcohol during treatment? 

As drinking alcohol alongside these medications can cause low blood pressure, it is recommended that you do not consume significant amounts of alcohol during treatment. If you are unsure, discuss with your prescribing doctor.  

Can thiazides cause allergic reactions? 

All substances may cause allergic reactions. You should inform your doctor of any allergies you have prior to use, and you can refer to the patient information leaflet that comes with your treatment, which lists the ingredients in the medication. 

Tablets may contain lactose, which some people may have an intolerance of.  

Can I buy thiazides over the counter?

No. Thiazides are only available on prescription. 

Can I buy thiazides online?

You can discuss thiazides and any related conditions with one of our GMC-registered clinicians via our online video consultation service. They are available for appointments between 9.30am-4.30pm, Monday to Friday. They can also provide referrals to specialists for treatment and fit notes, where suitable.  

Page last reviewed:  23/07/2020

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