Olmesartan Medoxomil/Hydrochlorothiazide (Olmetec Plus)
Is It Right for You?
A complete guide to Olmesartan Medoxomil/Hydrochlorothiazide (Olmetec Plus) — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Olmetec Plus?
Olmetec Plus is a fixed-dose combination antihypertensive tablet containing olmesartan medoxomil — an angiotensin II receptor blocker (ARB) — and hydrochlorothiazide (HCTZ) — a thiazide diuretic. It is available in two strengths: olmesartan 20 mg / HCTZ 12.5 mg and olmesartan 20 mg / HCTZ 25 mg.
Olmesartan blocks the effects of angiotensin II on blood vessels, reducing vasoconstriction and aldosterone-mediated salt and water retention; hydrochlorothiazide promotes urinary excretion of sodium and water, reducing circulating blood volume. This complementary dual mechanism addresses two independent drivers of elevated blood pressure, providing additive antihypertensive efficacy with generally good tolerability. Fixed-dose combination tablets improve adherence by reducing pill burden compared to taking two separate antihypertensive agents.
Olmetec Plus is a prescription-only medication in the UK. A clinician must assess your blood pressure, renal function, electrolyte levels, and medical history before prescribing.
What Conditions Is Olmetec Plus Used For?
Olmetec Plus is indicated for:
specifically for patients whose blood pressure is not adequately controlled on either olmesartan monotherapy or hydrochlorothiazide monotherapy alone; also used as initial combination therapy in patients with significantly elevated blood pressure where dual therapy is anticipated to be necessary from the outset
olmesartan provides additional renoprotective benefit in this group; the fixed combination may be used when diuretic therapy is also clinically indicated
through blood pressure lowering; the combination does not provide additional cardiovascular endpoint benefits beyond those attributable to blood pressure reduction
Olmetec Plus must typically be taken indefinitely. Stopping treatment without medical advice will result in blood pressure returning to elevated levels. Lifestyle modification — including salt restriction, regular aerobic exercise, healthy weight maintenance, and reduced alcohol intake — is an essential complement to pharmacological therapy and may allow dose reduction over time.
How Does Olmetec Plus Work?
Olmetec Plus combines two complementary mechanisms targeting different physiological pathways that regulate blood pressure:
Olmesartan medoxomil (ARB component): Olmesartan medoxomil is a prodrug that is completely hydrolysed during gastrointestinal absorption to olmesartan — the active form — which is a potent, selective, and irreversible competitive antagonist at the angiotensin II type 1 (AT1) receptor. Blockade of the AT1 receptor prevents angiotensin II from exerting its principal effects: vasoconstriction of vascular smooth muscle, aldosterone release from the adrenal cortex (which drives sodium and water retention), and stimulation of sympathetic nervous system activity. The result is arteriolar dilation, reduced aldosterone-mediated fluid retention, and a fall in blood pressure. Unlike ACE inhibitors, olmesartan does not inhibit bradykinin breakdown and therefore very rarely causes cough.
Hydrochlorothiazide (thiazide diuretic component): HCTZ inhibits the sodium/chloride cotransporter (NCC) in the distal convoluted tubule of the kidney, reducing the reabsorption of sodium and chloride from tubular fluid into the bloodstream. This increases urinary sodium and water excretion, reducing circulating blood volume and cardiac preload. HCTZ also has a direct mild vasodilatory effect on vascular smooth muscle. Plasma potassium loss is a recognised side effect (hypokalaemia), which is partially counteracted by the potassium-retaining effects of olmesartan's aldosterone suppression.
The combination therefore acts on both resistance vessels (through ARB-mediated vasodilation) and circulating volume (through diuresis), producing a more robust and sustained blood pressure reduction than either agent provides alone.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Take once daily at the same time each day. The combined long half-lives of both components provide 24-hour blood pressure coverage with once-daily dosing.
Can be taken with or without food. Food does not significantly affect the absorption of either component.
Maintain adequate fluid intake. The diuretic component increases fluid loss; maintain normal hydration, particularly in hot weather or during illness with vomiting or diarrhoea.
Take in the morning where possible. Taking a diuretic-containing preparation in the morning reduces the risk of nocturia (the need to urinate at night).
Do not stop suddenly without medical advice. Abrupt discontinuation risks blood pressure rebound; taper under clinical supervision.
Promptly report symptoms of dehydration. Dizziness, dry mouth, reduced urination, or muscle cramps may indicate volume depletion from the diuretic component — particularly during intercurrent illness.
Side Effects of Olmetec Plus
Most side effects are mild and resolve on their own. Serious side effects are rare but require immediate medical attention.
- Dizziness and lightheadedness (orthostatic hypotension)
- Hypokalaemia (low potassium)
- Hyponatraemia (low sodium)
- Increased blood urate and gout exacerbation
- Raised fasting glucose
- Acute kidney injury --- both ARBs and diuretics can precipitate acute renal deterioration
- Severe hypokalaemia --- cardiac arrhythmias may develop
- Angioedema --- swelling of the face, lips, tongue, or throat
- Severe hypotension --- particularly at initiation
A syndrome of severe chronic diarrhoea and significant weight loss has been specifically linked to olmesartan. It can develop months or years after starting the medication and resolves on discontinuation.
Drug Interactions
Olmetec Plus may interact with other medications, including aliskiren, lithium, and NSAIDs. Always inform your clinician about all medications you are taking.
although HCTZ lowers potassium, the ARB component raises it; net effect is variable; concurrent potassium-sparing agents may cause clinically significant hyperkalaemia.
blunt the antihypertensive effect of both ARBs and diuretics; increase the risk of acute kidney injury; avoid regular NSAID use.
hypokalaemia from HCTZ increases the risk of digoxin toxicity and drug-induced arrhythmias; monitor potassium closely.
no clinically significant interaction at standard doses.
Important Warnings
Olmesartan (as an ARB) is absolutely contraindicated during pregnancy. ARBs cause severe fetal harm — including fetal renal dysplasia, oligohydramnios, skull hypoplasia, and fetal death — during the second and third trimester. Women of childbearing potential must use effective contraception. If pregnancy is confirmed during treatment, Olmetec Plus must be stopped immediately and an alternative antihypertensive commenced.
Olmetec Plus is contraindicated in bilateral renal artery stenosis (or unilateral stenosis of a single functioning kidney) due to the risk of severe acute kidney injury.
Persistent unexplained chronic diarrhoea and significant weight loss in patients on olmesartan-containing medications must prompt clinical investigation and consideration of olmesartan as the causative agent. Discontinuation leads to resolution.
Serum electrolytes (sodium, potassium, creatinine, eGFR) must be checked before starting Olmetec Plus, 1–4 weeks after initiation or dose change, and then at least annually in stable patients. More frequent monitoring is required in patients with renal impairment, diabetes, or those on concurrent medications affecting electrolytes.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Olmetec Plus FAQs
Fixed-dose combination tablets such as Olmetec Plus improve treatment adherence by reducing the number of tablets you need to take each day. They also provide predictable combined pharmacology and have been shown to achieve better blood pressure control in patients requiring dual therapy. Where your clinician has already individually titrated both components, a fixed combination is a convenient step to simplify your regimen.
Yes. Renal function (eGFR, creatinine), serum potassium, and sodium should be checked before starting, 1–4 weeks after initiation or any dose change, and annually in stable patients. The HCTZ component can lower potassium and sodium, while the olmesartan component can raise potassium and affect renal function.
Possibly. Olmesartan has been specifically linked to a rare but serious sprue-like enteropathy causing chronic severe diarrhoea and significant weight loss — which can develop months or even years after starting the medication. If you are experiencing these symptoms, inform your clinician promptly so that olmesartan can be considered as the cause and appropriate investigations undertaken.
Regular NSAID use (ibuprofen, naproxen, diclofenac) should be avoided. NSAIDs blunt the antihypertensive effect of both olmesartan and HCTZ and, particularly in combination with an ARB and a diuretic (the "triple whammy"), significantly increase the risk of acute kidney injury. Paracetamol is the preferred analgesic for regular use in patients on antihypertensive therapy.
HCTZ raises serum uric acid levels and can precipitate acute gout attacks in susceptible patients. If you have a history of gout, inform your clinician before starting Olmetec Plus so that alternative diuretic combinations or additional urate-lowering therapy can be considered. Any acute joint pain, swelling, or redness during treatment should be reported promptly.