Abstract

Knee osteoarthritis (OA) is the most common degenerative joint disease worldwide and a leading cause of disability among older adults. Current treatment strategies focus primarily on symptom control through non-pharmacological interventions, analgesics, nonsteroidal anti-inflammatory drugs (NSAIDs), intra-articular therapies, and ultimately joint replacement for advanced disease. Diacerein is classified as a symptomatic slow-acting drug for osteoarthritis (SYSADOA) and has attracted attention because of its potential disease-modifying effects through inhibition of interleukin-1 beta (IL-1β), a key mediator in cartilage degradation. Despite promising biological mechanisms, clinical evidence regarding its efficacy remains controversial. This article reviews the pharmacology, mechanism of action, clinical trial evidence, safety profile, guideline recommendations, and current role of diacerein in the management of knee OA.

Introduction

Osteoarthritis is characterized by progressive degeneration of articular cartilage, remodeling of subchondral bone, synovial inflammation, and deterioration of joint function. Traditionally regarded as a purely mechanical "wear-and-tear" disease, OA is now recognized as a complex inflammatory disorder involving cytokine-mediated cartilage destruction.

Among these inflammatory mediators, IL-1β plays a critical role by promoting:

Chondrocyte catabolism
Matrix metalloproteinase (MMP) production
Cartilage matrix degradation
Synovial inflammation
Progressive joint destruction

Diacerein was developed as an anti-inflammatory SYSADOA targeting this pathway and has been used in several countries for symptomatic management of osteoarthritis.

Pharmacology of Diacerein

Classification

Diacerein belongs to the group of:

Symptomatic Slow-Acting Drugs for Osteoarthritis (SYSADOA)

Other SYSADOAs include:

Glucosamine sulfate
Chondroitin sulfate
Avocado soybean unsaponifiables (ASU)

Unlike NSAIDs, SYSADOAs generally have:

Delayed onset of action
Potential structural benefits
Longer-lasting effects after discontinuation

Mechanism of Action

Conversion to Rhein

After oral administration, diacerein is rapidly metabolized into its active metabolite:

Rhein

Rhein mediates the pharmacological effects of the drug.

IL-1β Inhibition

The principal mechanism involves suppression of IL-1β activity.

IL-1β normally causes:

Increased MMP production
Collagen degradation
Proteoglycan loss
Cartilage breakdown

Diacerein reduces these effects by:

Decreasing IL-1β synthesis
May reduce IL-1 receptor signaling
Reducing inflammatory cytokine release

These anti-interleukin-1 effects have been demonstrated in human osteoarthritic synovium and cartilage cultures.[2]

Effects on Cartilage

Experimental studies suggest that diacerein may:

Reduce Cartilage Catabolism

Decreases MMP-1
Decreases MMP-3
Decreases MMP-13

Promote Cartilage Repair

Enhances transforming growth factor-beta (TGF-β)
Stimulates extracellular matrix synthesis
Supports chondrocyte survival

Effects on Synovium

Diacerein may:

Reduce synovial inflammation
Lower cytokine production
Reduce inflammatory cell infiltration

These effects theoretically slow OA progression.

Pharmacokinetics

Absorption

Well absorbed orally
Bioavailability improved with food

Metabolism

Converted to rhein in the liver

Half-life

Approximately:

4–10 hours

Elimination

Predominantly renal excretion

Dose caution is advised in:

Chronic kidney disease
Elderly patients

The clinical pharmacokinetics of diacerein and its active metabolite rhein have been characterized in detail.[3]

Clinical Efficacy in Knee Osteoarthritis

Pain Reduction

Multiple randomized controlled trials have reported modest reductions in:

Knee pain
WOMAC pain scores
Analgesic consumption

However, the magnitude of benefit is generally small.

Meta-analyses have demonstrated:

Small but statistically significant improvements compared with placebo
Delayed onset of efficacy (typically 4–8 weeks)

Unlike NSAIDs, symptom improvement is not immediate.[1]

Functional Improvement

Some studies reported improvements in:

Walking distance
Stair climbing
Physical function scores

However, benefits were inconsistent among trials.

Structural Modification

A major theoretical advantage of diacerein is possible disease-modifying activity.

Several imaging studies suggested:

Slower joint-space narrowing
Reduced cartilage loss

Nevertheless, evidence remains insufficient to establish true disease-modifying osteoarthritis drug (DMOAD) status.

Therefore, diacerein remains classified as a SYSADOA rather than a confirmed DMOAD.

Recent High-Quality Evidence

A multicenter, double-blind, randomized placebo-controlled trial published in JAMA Internal Medicine in 2026 (262 participants, 24 weeks) evaluated diacerein specifically in patients with symptomatic knee OA and MRI-confirmed effusion-synovitis — the inflammatory phenotype in which IL-1β blockade would be most expected to help.[6]

Key Findings

No clinically meaningful reduction in knee pain
No superiority versus placebo
No improvement in function or in local knee inflammation
Higher incidence of diarrhea and gastrointestinal adverse effects

These findings challenge earlier positive studies and raise concerns regarding routine use.

The between-group difference in knee pain was just −1.3 mm on a 100 mm scale (95% CI, −9.8 to 7.3), far below any clinically meaningful threshold, while diarrhea was markedly more frequent with diacerein (38.6% vs 22.3% with placebo). Because the trial enriched for inflammatory disease yet still found no benefit, it argues strongly that diacerein's analgesic effect is negligible and unlikely to justify its adverse-event burden in most patients.[6]

Safety Profile

Gastrointestinal Adverse Effects

The most common adverse effect is:

Diarrhea

Reported in:

20–50% of patients in some studies

Consequences may include:

Dehydration
Electrolyte disturbances
Treatment discontinuation

This is the major limitation of diacerein therapy.[1]

Hepatotoxicity

Rare cases of:

Elevated liver enzymes
Drug-induced liver injury

have been reported.

Because of reports of serious drug-induced liver injury (including a fatal case of fulminant hepatitis), the European Medicines Agency (2014) made diacerein contraindicated in any patient with current or past liver disease. Before starting, patients should be screened for liver disease, and liver enzymes (LFTs) should be monitored during treatment. Diacerein should be stopped immediately if signs of liver problems (e.g. jaundice, dark urine with malaise, abdominal pain) occur, and avoided with other hepatotoxic medications.[5]

Urine Discoloration

A benign but common finding:

Dark yellow urine
Brown urine

Caused by renal excretion of rhein and its anthraquinone metabolites (a harmless coloured pigment).

Patients should be counseled to prevent unnecessary concern. However, dark urine together with feeling unwell, yellow eyes or skin, or abdominal pain is not benign — stop the drug and see a doctor.

Regulatory and Off-Label Status

Diacerein's regulatory status varies widely by region. In the European Union, a 2014 safety review by the EMA's Pharmacovigilance Risk Assessment Committee (PRAC) kept diacerein on the market but with restrictions: treatment should start at half the previous dose (50 mg/day), it is no longer recommended in patients aged 65 years or older, it must not be used in patients with liver disease or a history of liver disease, and it should be stopped if diarrhea develops.[5] Diacerein is not approved by the US FDA and is not marketed in the United States, so any US use would be considered off-label. It remains approved for osteoarthritis in many Asian, European, and Latin American countries. Readers should follow local labelling and prescribing regulations.

Contraindications

Diacerein should generally be avoided in:

Absolute

Hypersensitivity to diacerein
Any current or past liver disease (per EMA 2014; diacerein is contraindicated, not merely dose-adjusted)

Relative

Patients aged 65 years and older (the EMA 2014 review no longer recommends diacerein in this group because of the risk of severe diarrhea and dehydration)
Chronic diarrhea
Inflammatory bowel disease
Severe renal dysfunction
Pregnancy
Breastfeeding

Dosing

Adult Dose

Initial:

Diacerein 50 mg orally once daily with food for 2–4 weeks

Maintenance:

Diacerein 50 mg orally twice daily

This gradual initiation aims to reduce diarrhea. If diarrhea develops, the drug should be stopped (per EMA guidance) and a doctor consulted. These doses are for reference only — diacerein is a prescription medicine and should be started, adjusted, and monitored by a physician, not self-administered.

Comparison With Other OA Therapies

Therapy	Pain Relief	Onset	Structural Effect	Safety
NSAIDs	High	Days	None	GI/CV risk
Paracetamol	Low	Hours	None	Good
Intra-articular steroid	Moderate-High	Days	None	Temporary
Exercise therapy	Moderate	Weeks	Functional benefit	Excellent
Weight loss	Moderate	Weeks-Months	Disease benefit	Excellent
Diacerein	Low-Modest	4–8 weeks	Possible	Diarrhea
Knee arthroplasty	Very High	Immediate after recovery	Definitive	Surgical risk

Current Guideline Position

American College of Rheumatology (ACR)

The 2019 ACR/Arthritis Foundation osteoarthritis guideline does not endorse diacerein as a recommended pharmacological therapy. (Note: diacerein is not marketed in the United States, so it is not a named, individually graded recommendation in the US guideline; the guideline instead strongly recommends against the related SYSADOAs glucosamine and chondroitin for knee and hip OA.) International reviews comparing guidelines confirm that, where diacerein is assessed, major bodies do not recommend it as routine therapy.[4]

Preferred treatments include:

Exercise
Weight reduction
Topical NSAIDs
Oral NSAIDs
Intra-articular glucocorticoid injections
Duloxetine (selected patients)

NICE Guideline

NICE recommendations emphasize:

Therapeutic exercise
Weight management
Education
Topical NSAIDs

Diacerein is not included among primary recommended therapies.[7]

ESCEO

The European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO) recognizes SYSADOAs, including diacerein, as possible options in selected patients but generally not as first-line therapy.[8]

Practical Clinical Role

Today, diacerein occupies a limited niche role.

Potential candidates include:

Mild-to-moderate knee OA
Patients unable to tolerate NSAIDs
Patients seeking a slow-acting oral alternative
Individuals accepting uncertain benefit

Diacerein should not replace:

Exercise therapy
Weight reduction
Evidence-based analgesic strategies

Key Clinical Pearls

Advantages

✓ Targets inflammatory pathways involved in OA

✓ Possible cartilage-protective effects

✓ Does not cause NSAID-related gastric ulceration (but carries its own risks: frequent diarrhea and liver toxicity)

✓ May reduce analgesic requirements

Disadvantages

✗ Slow onset of action

✗ Frequent diarrhea

✗ Uncertain magnitude of benefit

✗ Weak evidence for structural modification

✗ Not strongly recommended by major international guidelines

Conclusion

Diacerein is a SYSADOA that exerts anti-inflammatory effects primarily through inhibition of IL-1β signaling. Although biological rationale and early clinical studies suggested potential symptomatic and structural benefits in knee osteoarthritis, more recent high-quality evidence — including a 2026 randomized trial enriched for inflammatory disease — has demonstrated limited clinical efficacy and significant gastrointestinal adverse effects. Current international guidelines do not recommend routine use of diacerein as a first-line treatment for knee OA. Its role is therefore restricted to selected patients who cannot tolerate standard therapies and who understand the modest expected benefits and potential risks.

Diacerein in Knee Osteoarthritis: Mechanisms, Evidence, Benefits, Risks, and Current Role