Diclofenac

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Diclofenac on Prescriptsy

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Diclofenac is a non-steroidal anti-inflammatory drug (NSAID) widely used in the United Kingdom for the relief of pain, inflammation, and fever.

It is one of the most extensively studied and prescribed anti-inflammatory medicines worldwide, with applications spanning musculoskeletal conditions, post-operative pain, acute injuries, and dysmenorrhoea.

Diclofenac is available in multiple formulations including standard-release and modified-release tablets, dispersible tablets, topical gels, suppositories, and injections.

Oral formulations are prescription-only medicines (POM) in the UK, while certain topical gel products are available as pharmacy (P) medicines.

Pain and inflammation are among the most common reasons patients consult a GP in the UK.

Osteoarthritis alone affects over 8.5 million people in England, while rheumatoid arthritis affects approximately 400,000 adults.

Acute musculoskeletal injuries, post-surgical pain, and primary dysmenorrhoea account for millions of additional consultations each year.

NSAIDs remain the pharmacological cornerstone for many of these conditions, and diclofenac is distinguished within the class by its potent anti-inflammatory efficacy and the breadth of its evidence base.

However, important safety considerations, particularly regarding cardiovascular and gastrointestinal risk, mean that prescribing must be carefully individualised.

This page provides a comprehensive clinical overview of diclofenac, covering its mechanism of action, dosing, side effects, safety warnings, drug interactions, and how to obtain it in the UK.

Important safety information about diclofenac

Before reading further, note the following essential safety points.

• Diclofenac is contraindicated in patients with established cardiovascular disease (heart disease, stroke, peripheral arterial disease) and severe heart failure. The MHRA classifies its cardiovascular risk as similar to COX-2 selective inhibitors.
• All NSAIDs, including diclofenac, can cause gastrointestinal bleeding and peptic ulceration. Take oral diclofenac with food and report any signs of GI bleeding (dark stools, vomiting blood) immediately.
• Use the lowest effective dose for the shortest necessary duration.
• Do not take diclofenac with other NSAIDs (including ibuprofen and naproxen) or low-dose aspirin without medical advice.
• Diclofenac must not be used in the third trimester of pregnancy.
• Seek emergency medical help (call 999 or attend A&E) for signs of heart attack, stroke, GI bleeding, or a severe allergic reaction.

Understanding pain and inflammation

When tissues are damaged by injury, infection, or autoimmune processes, cells release arachidonic acid from their membranes.

Cyclooxygenase (COX) enzymes convert arachidonic acid into prostaglandins, prostacyclin, and thromboxane A2.

Prostaglandins, particularly PGE2, sensitise peripheral pain receptors (nociceptors) to mechanical and chemical stimuli, lower the pain threshold, and promote the cardinal signs of inflammation: redness (rubor), heat (calor), swelling (tumor), and pain (dolor).

They also act on the hypothalamic thermoregulatory centre to produce fever.

Two main COX isoforms are clinically relevant. COX-1 is constitutively expressed in most tissues and produces prostaglandins that maintain gastric mucosal integrity, platelet aggregation, and renal blood flow.

COX-2 is induced at sites of inflammation and is the primary source of pro-inflammatory prostaglandins.

The therapeutic effects of NSAIDs derive primarily from COX-2 inhibition, while many of their adverse effects (gastrointestinal injury, renal impairment, bleeding tendency) result from COX-1 inhibition.

How diclofenac works: mechanism of action

Diclofenac is a potent inhibitor of both COX-1 and COX-2, with a relative selectivity for COX-2 that is greater than that of traditional NSAIDs such as naproxen and ibuprofen, though less selective than celecoxib.

This COX-2 preference contributes to its strong anti-inflammatory potency.

By reducing prostaglandin synthesis at sites of tissue injury and inflammation, diclofenac alleviates pain, reduces inflammatory swelling, restores joint mobility, and lowers fever.

Beyond COX inhibition, diclofenac has additional pharmacological actions that may contribute to its clinical efficacy.

It partially inhibits the lipoxygenase pathway, reducing leukotriene production, and modulates the thromboxane-prostacyclin balance. Some evidence suggests it may also affect ion channels involved in pain signalling.

These multiple mechanisms may help explain why diclofenac is considered one of the most effective NSAIDs for inflammatory pain in head-to-head comparative studies.

The COX-2 selectivity of diclofenac is, however, a double-edged sword.

It is the same property that underpins the heightened cardiovascular risk observed with COX-2 selective inhibitors and with diclofenac, as reduced prostacyclin (a vasodilator and inhibitor of platelet aggregation) without proportional reduction in thromboxane A2 may promote a prothrombotic state.

Clinical evidence and MHRA safety guidance

Diclofenac has been available for over 40 years and is supported by an extensive body of clinical trial evidence.

Systematic reviews and meta-analyses consistently rank it among the most effective oral NSAIDs for pain relief in osteoarthritis, rheumatoid arthritis, acute musculoskeletal injury, and post-operative pain.

The Cochrane Collaboration has published multiple reviews supporting its efficacy across these indications.

In 2013, following a major meta-analysis by the Coxib and Traditional NSAID Trialists' (CNT) Collaboration involving over 353,000 patients, the MHRA issued updated safety advice.

The CNT analysis confirmed that diclofenac 150 mg daily was associated with approximately one additional major vascular event per 1,000 patient-years compared with placebo, a risk magnitude similar to that of the COX-2 selective inhibitor celecoxib.

In contrast, naproxen and low-dose ibuprofen showed lower cardiovascular risk.

The MHRA subsequently reclassified diclofenac, contraindicating it in patients with established cardiovascular disease and advising caution in those with cardiovascular risk factors.

Despite these restrictions, diclofenac remains a valuable option for patients without cardiovascular disease who require potent anti-inflammatory therapy, particularly when other NSAIDs have been ineffective or poorly tolerated.

Dosage and administration

The fundamental prescribing principle for all NSAIDs, including diclofenac, is to use the lowest effective dose for the shortest necessary duration.

Standard-release diclofenac sodium tablets are typically prescribed as 25 mg or 50 mg two to three times daily with food, up to a maximum of 150 mg per day.

Modified-release (MR) formulations are available as 75 mg (taken twice daily or once daily depending on formulation) or 100 mg once daily, providing convenient dosing for chronic conditions such as arthritis.

Diclofenac potassium tablets are formulated for more rapid absorption and are often preferred for acute pain states and dysmenorrhoea.

The usual dose is 50 mg two to three times daily.

For period pain, treatment should begin at the onset of symptoms and continue for 2 to 3 days per cycle.

Topical diclofenac gel (such as Voltarol Emulgel) is applied to the skin over the affected area two to four times daily, depending on the formulation strength.

It provides effective local anti-inflammatory and analgesic action for conditions including osteoarthritis of the knee and hand, sprains, strains, and tendinopathy.

Systemic absorption from topical application is approximately 6% of that from oral dosing, significantly reducing the risk of systemic side effects.

Elderly patients should receive the lowest effective dose. No specific dose adjustment is required in mild to moderate renal impairment, but diclofenac is contraindicated in severe renal failure. In hepatic impairment, use the lowest dose and monitor liver function.

Side effects of diclofenac

Gastrointestinal side effects

Gastrointestinal adverse effects are the most common and include nausea, dyspepsia (indigestion), abdominal pain, diarrhoea, and flatulence.

More serious GI complications include gastric and duodenal ulceration, gastrointestinal bleeding (which may present as dark tarry stools or vomiting blood), and rarely gastrointestinal perforation.

These events can occur at any time during treatment, with or without prior warning symptoms, and can be fatal.

The risk is highest in elderly patients, those with a history of peptic ulcer disease, and those taking concurrent medications that affect the GI tract (anticoagulants, corticosteroids, SSRIs).

Cardiovascular side effects

Diclofenac, particularly at the 150 mg daily dose, is associated with an increased risk of atherothrombotic events including myocardial infarction and ischaemic stroke.

This risk is similar to that of COX-2 selective inhibitors. The risk increases with dose and duration of use.

NSAIDs including diclofenac can also cause fluid retention, oedema, and worsening of pre-existing hypertension or heart failure.

Renal side effects

NSAIDs inhibit prostaglandin-mediated renal blood flow regulation, which can lead to fluid retention, peripheral oedema, hypertension, hyperkalaemia, and deterioration of renal function.

Acute kidney injury is rare but can occur, particularly in patients who are dehydrated, elderly, or taking concurrent ACE inhibitors, ARBs, or diuretics.

Adequate hydration should be maintained during treatment.

Hepatic side effects

Elevated liver transaminases occur in a small proportion of patients and are usually reversible on discontinuation. Severe hepatotoxicity, including fulminant hepatitis and liver failure, has been reported rarely. If long-term treatment is planned, liver function tests should be checked periodically.

Other side effects

Less common adverse effects include headache, dizziness, skin rashes, photosensitivity, tinnitus, and visual disturbance.

Serious hypersensitivity reactions including angioedema, bronchospasm, and anaphylaxis can occur, particularly in patients with a history of aspirin-sensitive asthma.

Severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis) are very rare but potentially life-threatening.

When to seek medical advice

Seek emergency medical attention (call 999 or attend A&E) if you experience signs of GI bleeding (vomiting blood, dark or black tarry stools), chest pain, signs of stroke (sudden weakness, speech difficulty, facial drooping), severe allergic reaction (throat swelling, difficulty breathing, collapse), or a widespread blistering skin rash.

Contact your GP or NHS 111 for persistent indigestion, unusual bruising, ankle swelling, dark urine, jaundice, or any new symptoms that concern you.

Report suspected adverse reactions via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk .

Warnings and precautions

Cardiovascular risk

Diclofenac is contraindicated in patients with established ischaemic heart disease, cerebrovascular disease, peripheral arterial disease, and severe heart failure (NYHA class III-IV).

For patients with cardiovascular risk factors (hypertension, dyslipidaemia, diabetes, smoking, family history of premature cardiovascular disease), alternative analgesics should be considered first.

If diclofenac is used, the lowest dose for the shortest duration should be prescribed, with regular cardiovascular risk review.

Gastrointestinal protection

Co-prescribing a proton pump inhibitor (PPI) such as omeprazole or lansoprazole is recommended for patients at increased GI risk, including those aged 65 and over, those with a history of peptic ulcer disease or GI bleeding, and those taking concurrent anticoagulants, corticosteroids, antiplatelet agents, or SSRIs.

If a patient develops GI bleeding, diclofenac must be stopped immediately.

Renal considerations

Renal function should be monitored in patients with pre-existing kidney disease, heart failure, liver cirrhosis, dehydration, or concurrent use of medicines affecting renal haemodynamics (ACE inhibitors, ARBs, diuretics). Patients should maintain adequate fluid intake throughout treatment.

Drug interactions

Diclofenac has numerous clinically important drug interactions. It should not be combined with other NSAIDs (including over-the-counter ibuprofen) due to additive GI and cardiovascular risk.

Concurrent use with anticoagulants (warfarin, DOACs), antiplatelet agents (clopidogrel, aspirin), corticosteroids, and SSRIs increases the risk of bleeding.

Diclofenac may increase plasma levels of lithium, methotrexate, digoxin, and ciclosporin. It can reduce the efficacy of ACE inhibitors, ARBs, and diuretics.

The combination of an NSAID with an ACE inhibitor or ARB plus a diuretic (the "triple whammy") significantly increases the risk of acute kidney injury and should be avoided where possible.

Pregnancy and breastfeeding

Diclofenac is contraindicated in the third trimester of pregnancy due to the risk of premature closure of the foetal ductus arteriosus, inhibition of uterine contractions, and oligohydramnios.

Use in the first and second trimesters should be avoided unless clearly necessary. Diclofenac passes into breast milk in small amounts.

Short-term use at the lowest effective dose is generally considered compatible with breastfeeding, but discuss this with your prescriber or pharmacist.

Diclofenac compared with other NSAIDs

The UK market offers several NSAIDs with differing risk-benefit profiles.

Ibuprofen (at doses up to 1,200 mg daily) and naproxen have lower cardiovascular risk than diclofenac and are generally preferred for patients with cardiovascular risk factors.

However, diclofenac is considered more effective than ibuprofen for inflammatory pain in some studies and may be the preferred choice for patients without cardiovascular disease who have not responded to other NSAIDs.

Topical diclofenac gel offers an alternative that avoids most systemic risks while providing effective local relief for superficial musculoskeletal conditions.

How to get diclofenac in the UK

Oral diclofenac is a prescription-only medicine. Your GP can prescribe it following a clinical assessment that includes evaluation of cardiovascular risk, gastrointestinal risk, renal function, and current medications.

The standard NHS prescription charge in England is currently 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

Topical diclofenac gel (such as Voltarol Pain-eze Emulgel) is available as a pharmacy medicine and can be purchased from community pharmacies without a prescription following a consultation with the pharmacist.

This is a suitable option for short-term relief of localised muscle and joint pain in adults.

Authorised online prescribers registered with the General Pharmaceutical Council (GPhC) may also prescribe oral diclofenac following a suitable clinical assessment.

Practical tips for managing pain with diclofenac

Always take oral diclofenac with or after food to reduce gastric irritation. Do not lie down for at least 30 minutes after taking a tablet.

If you are prescribed regular treatment, take doses at evenly spaced intervals throughout the day.

For acute conditions, start treatment as early as possible and stop once the pain or inflammation has resolved.

For chronic conditions such as arthritis, combine diclofenac with non-pharmacological measures including regular physical activity, weight management, physiotherapy, and joint protection strategies.

If you are using topical diclofenac gel, apply a thin layer to the affected area and rub in gently. Wash your hands after application (unless treating the hands).

Do not apply to broken skin, wounds, or mucous membranes, and avoid covering the area with airtight dressings unless directed by your prescriber.

When to seek further medical advice

Contact your GP or NHS 111 if your pain does not improve within a few days, if you experience persistent indigestion despite taking diclofenac with food, or if you develop new symptoms during treatment.

Seek emergency care (call 999 or attend A&E) for signs of GI bleeding, heart attack, stroke, severe allergic reaction, or widespread skin blistering.

Report any suspected adverse reactions via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk .

Sources

• Diclofenac Sodium 50 mg Gastro-resistant Tablets, Summary of Product Characteristics (EMC)
• Diclofenac sodium, British National Formulary (BNF)
• NICE CKS: NSAIDs, prescribing issues
• Diclofenac, NHS
• MHRA Drug Safety Update: Diclofenac
• MHRA Yellow Card Scheme