The WHO Analgesic Ladder: Applying Stepwise Pain Relief Safely
The WHO analgesic ladder is a practical framework for selecting analgesia according to the severity, mechanism, and effect of pain. Originally developed in 1986 for cancer pain, its core principles—careful assessment, regular review, appropriate escalation, and individualised care—remain the cornerstone of pain management across all clinical practice.
It is crucial to remember that the ladder is not a substitute for diagnosis: relieving pain must occur alongside the aggressive investigation and treatment of the underlying cause.
Learning outcomes
- Describe the classical steps of the WHO analgesic ladder and its modern (bidirectional) application.
- Assess pain systematically before choosing an analgesic using validated tools (e.g., SOCRATES, numerical scales).
- Detail the pharmacology (Mechanism of Action, Indications, Contraindications, Adverse Effects, Interactions) of non-opioids, opioids, and adjuvants.
- Recognise when it is appropriate to move directly to strong opioid therapy, refer, or treat the cause of pain urgently.
- Prevent, monitor, and manage common adverse effects of analgesics, particularly opioid-induced respiratory depression and constipation.
1. The place of the ladder in modern pain care
The classical ladder features ascending steps. However, modern clinical pharmacology teaches that the ladder is bidirectional. The central aim is not to force a patient to “climb” from step 1; it is to achieve acceptable comfort, function, sleep, and quality of life with the least harm.
Do not apply the steps mechanically
- A patient with severe cancer pain, a major fracture, acute myocardial ischaemia, bowel obstruction, compartment syndrome, spinal cord compression, sepsis, or an acute abdomen requires immediate strong analgesia (Step 3) alongside urgent definitive treatment.
- In severe established cancer or acute trauma pain, a patient appropriately begins at the strong-opioid step rather than being made to “fail” weaker treatments first.
- Conversely, as acute pain resolves (e.g., post-operatively), the ladder should be climbed downwards (de-escalation) to prevent opioid dependence.
Pain is a symptom, not the diagnosis
Escalating analgesics without looking for a reversible cause can be highly dangerous. New severe back pain with weakness or sphincter disturbance (Cauda Equina/Spinal Cord Compression), sudden severe headache (Subarachnoid Haemorrhage), chest pain, peritonism, a painful cold limb (Ischaemia), or pain with fever and instability needs urgent assessment and escalation of care—not merely a higher analgesic dose.
2. Start with a proper pain assessment
Ask the patient to describe pain in their own words and document a baseline. Use the SOCRATES or PQRST mnemonic. A numerical rating scale (0–10), verbal scale, or Wong-Baker faces scale can be used, but the number alone is insufficient.
| Assessment domain | Questions and clinical meaning |
|---|---|
| Site and radiation | Where is it? Does it move? Map focal, dermatomal, bone, or visceral distribution. |
| Onset, timing, and pattern | Sudden or gradual? Constant, intermittent, incident-related, or nocturnal? New pain in a cancer patient may be a new complication (e.g., pathological fracture). |
| Quality (Mechanism) | Burning, electric shock, shooting (Neuropathic); Aching, tender, throbbing (Somatic Nociceptive); Cramping, colicky, deep pressure (Visceral Nociceptive). |
| Severity and functional effect | How does it affect walking, breathing, sleep, eating, work, mood, and personal care? Functional goals guide treatment. |
| Triggers and relief | Movement, cough, meals, position, dressing changes. Identifies incident pain requiring planned rescue doses. |
| Previous treatment | What drug, route, dose, timing, and adverse effects? Confirm adherence, availability, and use of traditional/herbal medicines. |
| Context and Comorbidities | Renal/hepatic disease, pregnancy, bleeding risk, substance-use history, depression/anxiety, family support, and medicine access. |
Breakthrough Pain
Breakthrough pain is a transient flare of pain despite otherwise controlled background pain. Ask whether it is predictable (incident pain, e.g., during wound care) or spontaneous; this changes the pharmacological rescue plan.
3. The classical WHO analgesic ladder
| Step | Usual pain severity | Analgesic strategy | Key message |
|---|---|---|---|
| Step 1 | Mild pain (1-3/10) | Non-opioid: paracetamol and/or an NSAID, ± adjuvant. | Use a safe, regular regimen; avoid NSAID duplication and assess organ risk. |
| Step 2 | Mild-to-moderate pain (4-6/10) that persists despite step 1 | Weak Opioid (codeine, tramadol) ± non-opioid ± adjuvant. | Review early. A weak opioid is not always the best bridge to a strong opioid; sometimes it just delays effective relief. |
| Step 3 | Moderate-to-severe pain (7-10/10), persistent or escalating | Strong opioid (morphine, fentanyl) ± non-opioid ± adjuvant. | Individual titration, prevention of adverse effects (constipation, nausea), and regular monitoring are essential. |
| Step 4 (Modern addition) | Refractory, intractable pain | Interventional procedures (nerve blocks, epidurals, neurolysis, PCA) ± adjuvant. | Requires specialist pain/anaesthesia referral. |
4. The five practical principles of WHO pain management
- By the mouth: Use the least invasive effective route. Oral treatment supports comfort and home care. Use IV/SC routes only when vomiting, dysphagia, malabsorption, or rapid titration makes oral therapy unsuitable. Avoid painful IM injections.
- By the clock: Persistent pain needs regular scheduled analgesia (e.g., q6h or q12h), not only PRN (when pain becomes unbearable). Add a separate PRN plan for predictable breakthrough or procedural pain.
- By the ladder: Choose the step that matches the patient’s present pain and clinical situation. Escalate, de-escalate, or bypass a step when clinically indicated.
- For the individual: Choose the agent, route, and monitoring plan tailored to that patient’s pain mechanism, organ function (renal/hepatic clearance), co-morbidity, beliefs, and treatment goals.
- Attention to detail: Write clear instructions, check understanding, anticipate constipation/nausea, check drug interactions, and review response. Good prescribing is only effective when the patient can follow the plan.
5. Step 1: Non-Opioid Analgesics (Pharmacology Deep-Dive)
Paracetamol (Acetaminophen)
- Mechanism of Action (MOA): Exact mechanism debated. Believed to inhibit COX-3 in the CNS and interact with the peroxidase site of COX enzymes. Has potent analgesic and antipyretic effects, but virtually no anti-inflammatory effects in the periphery.
- Indications: Mild nociceptive pain, fever, osteoarthritis (mild), adjunct to opioids for severe pain (opioid-sparing effect).
- Contraindications: Severe active liver disease.
- Adverse Effects: Extremely well tolerated at therapeutic doses. Overdose depletes hepatic glutathione, causing accumulation of the toxic metabolite NAPQI, leading to fatal centrilobular hepatic necrosis.
- Interactions & Dosing: 1g every 6 hours (max 4g/day in healthy adults). Reduce max dose (e.g., 2g-3g/day) in malnutrition, frailty, chronic alcoholism, or liver disease. Beware of accidental duplication in OTC cold remedies.
NSAIDs (Ibuprofen, Diclofenac, Naproxen, Celecoxib)
- Mechanism of Action (MOA): Reversibly inhibit Cyclooxygenase (COX-1 and COX-2) enzymes, preventing the conversion of arachidonic acid to prostaglandins and thromboxanes. This reduces peripheral inflammation, pain receptor sensitization, and fever. (Celecoxib is selectively COX-2).
- Indications: Inflammatory musculoskeletal pain, bone metastases, gout, dysmenorrhoea, post-operative inflammatory pain.
- Contraindications: Active peptic ulcer disease, acute GI bleeding, severe renal impairment (eGFR <30), severe heart failure, third trimester of pregnancy (premature closure of ductus arteriosus), NSAID-induced asthma.
- Adverse Effects:
- GI: Dyspepsia, gastric ulceration/bleeding (due to COX-1 inhibition reducing protective gastric mucus).
- Renal: Acute kidney injury (due to inhibition of vasodilatory prostaglandins acting on the afferent arteriole).
- CVS: Fluid retention, hypertension, increased MI/stroke risk (especially COX-2 inhibitors and Diclofenac).
- Interactions: Increases bleeding risk with anticoagulants/SSRIs. Blunts effects of antihypertensives (ACE inhibitors, diuretics).
Step 1 prescribing traps
- Using a combination cold/flu product without noticing additional paracetamol (risk of hepatotoxicity).
- Giving two NSAIDs together because one “did not work” (massively increases toxicity without adding benefit).
- Continuing an NSAID during dehydration, acute kidney injury, sepsis, or GI bleeding.
- Failing to reassess severe pain because a low-risk drug was prescribed first.
6. Step 2: Opioids for mild-to-moderate pain
Step 2 agents have a “ceiling effect” for analgesia but no ceiling for toxicity. Do not assume “weak opioid” means harmless. Assess sedation, respiratory rate, cognition, falls risk, and constipation at every review.
Codeine
- MOA: A weak prodrug. It must be metabolized in the liver by the enzyme CYP2D6 into morphine to exert its µ-opioid analgesic effect.
- Pharmacogenetics: Highly variable. Poor metabolizers get no pain relief. Ultra-rapid metabolizers (more common in certain African and Middle Eastern populations) convert it rapidly to morphine, risking fatal respiratory depression even at normal doses.
- Contraindications: Children under 12, breastfeeding mothers, acute respiratory depression.
- Adverse Effects: Severe constipation, nausea, drowsiness.
Tramadol
- MOA: Dual action. 1) Weak µ-opioid receptor agonist. 2) Serotonin and Norepinephrine Reuptake Inhibitor (SNRI) in the descending pain pathways.
- Indications: Moderate nociceptive and neuropathic pain.
- Contraindications: Uncontrolled epilepsy, patients taking MAOIs.
- Adverse Effects: Nausea, dizziness, lowers the seizure threshold (can cause seizures at high doses).
- Interactions: High risk of Serotonin Syndrome if combined with SSRIs, SNRIs, or TCAs. Metabolism relies on CYP2D6 and CYP3A4.
Clinical Note: A patient whose pain is genuinely severe or rapidly escalating may be better served by carefully titrated strong opioid therapy (Step 3) rather than repeated escalation of a weak opioid that has reached its ceiling effect.
7. Step 3: Strong opioids for moderate-to-severe pain
Morphine (The Gold Standard)
- MOA: Full, potent agonist at µ (mu) opioid receptors in the CNS and GI tract. Hyperpolarizes nociceptive neurons and inhibits substance P release.
- Pharmacokinetics: Metabolised in the liver to Morphine-3-glucuronide (M3G – causes neuroexcitation/myoclonus) and Morphine-6-glucuronide (M6G – highly potent analgesic). Both are renally excreted.
- Indications: Severe acute pain, trauma, myocardial infarction, advanced cancer pain, palliative care.
- Contraindications / Cautions: Renal failure (M6G accumulation causes prolonged fatal apnoea), raised intracranial pressure, acute asthma.
- Adverse Effects: Respiratory depression, intense constipation, nausea/vomiting, histamine release (causes pruritus/itching and hypotension), miosis (pinpoint pupils), urinary retention.
Fentanyl
- MOA: Highly potent, synthetic µ-opioid agonist (100x more potent than morphine). Highly lipophilic.
- Indications: Perioperative analgesia, severe chronic cancer pain (via transdermal patch).
- Advantages: Does not release histamine (hemodynamically stable). Has no active metabolites (the opioid of choice in severe renal failure).
- Adverse Effects: Profound respiratory depression. Chest wall rigidity if pushed rapidly IV.
Methadone
- MOA: µ-opioid agonist AND NMDA receptor antagonist.
- Indications: Opioid use disorder maintenance, severe refractory neuropathic pain (due to NMDA antagonism).
- Cautions: Extremely long, unpredictable half-life (risk of delayed overdose). Prolongs the QTc interval (risk of Torsades de Pointes). Requires specialist prescribing.
Safe strong-opioid initiation and review
- Titration: Start with an appropriate formulation (immediate release for acute titration, modified release for background chronic pain).
- Rescue Dosing: Always prescribe a PRN immediate-release rescue dose (usually 1/6th of the total daily background dose) for breakthrough pain. Do not write vague instructions like “morphine as needed.”
- Anticipate Side Effects: Prevent constipation from day one (prescribe a stimulant laxative like bisacodyl or senna). Prescribe an antiemetic (e.g., metoclopramide or haloperidol) for the first few days.
- Monitor: Document baseline pain, alertness, respiratory rate, renal function, and concurrent sedatives.
Opioid toxicity and overdose
Concerning features include increasing drowsiness, difficult arousal, slow or shallow breathing (RR < 10), pinpoint pupils, cyanosis, and hypotension. Stop further opioid, call for urgent help, support airway and breathing with a Bag-Valve-Mask (BVM), and use Naloxone (a competitive µ-opioid antagonist) according to protocol.
Caution: In a patient receiving long-term opioids for cancer/palliative pain, aggressive reversal may precipitate severe, agonizing pain and massive withdrawal; this requires senior, highly titrated management, not an automatic bolus.
8. Adjuvant analgesics: match treatment to the pain mechanism
Adjuvants are medicines with another primary indication that can improve selected pain syndromes or address an underlying cause. They are not “extra tablets for every patient.” Choose them deliberately and explain that their onset may be slower than conventional analgesics.
| Pain situation | Possible adjuvant approach & Pharmacology | Important clinical cautions |
|---|---|---|
| Neuropathic pain (burning, shooting, electric, allodynia) | Anticonvulsants: Gabapentin/Pregabalin (block voltage-gated Ca2+ channels). Antidepressants: Amitriptyline/Duloxetine (increase synaptic 5-HT/NE to boost descending pain inhibition). |
Assess for severe sedation, dizziness, falls, anticholinergic effects (Amitriptyline), and mood changes. Gabapentinoids require renal dose adjustment. Medicine must be titrated up gradually. |
| Bone metastasis or inflammatory tumour pain | NSAIDs (inhibit osteoclast-activating prostaglandins). Bisphosphonates (inhibit osteoclast bone resorption). Disease-directed treatments like radiotherapy. |
Do not rely on analgesics alone when orthopaedic stabilisation or oncological treatment is needed to prevent pathological fracture or cord compression. |
| Raised intracranial pressure or nerve/capsular stretch | Corticosteroids (Dexamethasone): Potent anti-inflammatory; reduces peritumoral oedema. | Watch for hyperglycaemia, immunosuppression, mood changes/psychosis, proximal myopathy, gastritis, and the need for a slow taper. |
| Colicky visceral pain / Bowel obstruction | Antispasmodics: Hyoscine butylbromide (Buscopan) blocks muscarinic receptors in smooth muscle. | Abdominal pain with vomiting, distension, or guarding requires urgent surgical diagnostic review. Do not mask peritonism. |
| Spasticity or severe muscle spasm | Muscle relaxants: Baclofen (GABA-B agonist), Diazepam (GABA-A modulator). | Sedating medicines compound opioid-related respiratory depression and dramatically increase falls risk. |
9. Non-drug and disease-directed treatment belong on every step
Effective pain care is multidisciplinary. Pharmacological agents are only one pillar of the WHO approach.
- Physical: Positioning, splinting, heat or cold where appropriate, physiotherapy, exercise/rehabilitation.
- Psychological: Explanation and reassurance, sleep support, relaxation, CBT, social and spiritual support. Good communication reduces fear (which neurochemically amplifies pain).
- Disease-directed: Treat the root cause. Drain an abscess, reduce a fracture, treat an infection, relieve urinary retention with a catheter, operate on a surgical abdomen, or use radiotherapy for bone metastases.
9A. Writing a safe analgesic prescription
A good prescription makes the intended plan visible to every member of the team and to the patient. Specify the drug, formulation, route, dose, frequency, maximum permitted rescue use, indication, and review time.
- For an opioid: Record whether it is background (modified-release) or rescue (immediate-release) treatment, the patient’s previous opioid exposure (opioid-naïve vs tolerant), and the bowel/nausea plan.
- For an NSAID: Record the reason it is appropriate and any gastroprotection (e.g., Omeprazole) or renal monitoring required.
Teach patients and caregivers to store controlled medicines securely. In chronic non-cancer pain, set a functional goal (e.g., sleeping through the night, mobilising to the toilet) rather than pursuing complete absence of all sensation at the cost of heavy, dangerous sedation.
9B. The pain mechanism changes the plan
- Somatic nociceptive pain: Well localised, aching, or sharp; worse with movement. Look for inflammation, fracture, or wound complication. Responds well to NSAIDs, Paracetamol, and Opioids.
- Visceral nociceptive pain: Deep, poorly localised, cramping; may have autonomic symptoms (nausea, sweating). Treat the organ cause. Responds to opioids and antispasmodics.
- Neuropathic pain: Burning, electric, shooting. Often needs a mechanism-specific adjuvant (Gabapentin/Amitriptyline). Responds incompletely to opioids alone.
10. Monitoring, de-escalation, and referral
Reassess after starting or changing treatment: pain at rest and on movement, function, breakthrough episodes, adverse effects, adherence, and the patient’s own treatment goal.
- The Reassessment Question: “What changed after the last intervention—pain intensity, ability to move or sleep, breakthrough episodes, adverse effects, or the underlying disease?” The answer determines whether to continue, change, escalate, de-escalate, or investigate.
- De-escalation: If acute pain is controlled and the tissue healing has progressed, step down to the lowest effective regimen (Step 3 -> Step 2 -> Step 1) rather than continuing high-risk drugs indefinitely.
- Referral: Seek specialist palliative care, pain medicine, anaesthesia, or oncology support for complex pain, rapid dose escalation, intolerable adverse effects, difficult opioid conversions (e.g., switching from oral morphine to fentanyl patches), or suspected misuse/diversion.
11. Children, acute pain, and special situations
- Paediatrics: The classical 3-step adult cancer-pain ladder should not be used as a rigid dosing tool for children. WHO guidelines for children utilize a two-step strategy (Step 1: Paracetamol/Ibuprofen; Step 2: Strong opioid like Morphine). Codeine is generally contraindicated in children due to unpredictable CYP2D6 metabolism. Pain requires weight-based prescribing and age-appropriate assessment scales (e.g., FLACC scale).
- Acute severe pain: Delaying adequate treatment because a patient has not “tried the lower step” is poor practice. Use a descending/bidirectional ladder approach.
- Organ Impairment: Pregnancy, frailty, renal impairment (avoid NSAIDs, Codeine, Morphine; prefer Fentanyl or Buprenorphine), hepatic impairment, and concurrent alcohol or benzodiazepine use drastically alter the benefit–risk balance, demanding lower doses, longer intervals, and senior input.
12. Worked clinical reasoning examples
Example 1: Mild inflammatory knee pain (Osteoarthritis exacerbation)
Reasoning: Assess diagnosis, rule out septic arthritis (red flag), and check renal/GI/CVS risk. Start with non-drug measures (weight loss, physiotherapy) and a non-opioid plan. Prescribe topical NSAIDs first. If oral is needed, prescribe short-course Ibuprofen with meals. Do not give oral Diclofenac and Ibuprofen together. Review functional mobility.
Example 2: Advanced cancer with severe, constant spinal bone pain
Reasoning: Assess severity, risk of pathological fracture, or spinal cord compression (red flag). Severe pain (9/10) justifies skipping Step 1/2 and starting Step 3 strong opioids immediately (e.g., regular modified-release Morphine + PRN immediate-release Morphine). Co-prescribe laxatives and antiemetics. Add an NSAID or Corticosteroid as an adjuvant for bone pain. Refer for palliative radiotherapy.
Example 3: Burning, bilateral diabetic foot pain, worse at night
Reasoning: The description strongly suggests neuropathic pain. Simply escalating Paracetamol or NSAIDs will fail and risk organ damage. Assess the foot urgently for infection/ischaemia. Optimise glycemic control. Initiate a mechanism-specific adjuvant (e.g., low-dose nightly Amitriptyline or Gabapentin), counsel on slow onset of action, and monitor for dizziness.
13. OSCE and exam pearls
- State the ladder clearly, but immediately demonstrate advanced clinical thinking: “Assess the cause and mechanism of pain; treat the patient, not the number.”
- For persistent pain, explain “by the clock”: regular background analgesia plus a clear, prescribed PRN plan for breakthrough pain.
- When prescribing any opioid in an OSCE, explicitly state you will prescribe a stimulant laxative to prevent constipation, an antiemetic, and monitor respiratory rate/sedation.
- When prescribing an NSAID, verbally verify renal function (eGFR), GI ulcer history, asthma, and bleeding risk; never combine two NSAIDs.
- In severe pain or red-flag presentations (trauma, ischemia), explicitly state that you will provide adequate strong analgesia immediately while resuscitating, rather than forcing step-by-step progression.
Knowledge check
1. What are the classical steps of the WHO analgesic ladder?
Step 1: Non-opioid (Paracetamol/NSAID) ± adjuvant. Step 2: Weak opioid (Codeine/Tramadol) ± non-opioid ± adjuvant. Step 3: Strong opioid (Morphine/Fentanyl) ± non-opioid ± adjuvant.
2. Give three features that suggest neuropathic rather than nociceptive pain.
Pain described as burning, electric shocks, shooting, pins-and-needles, or pain triggered by normally painless light touch (allodynia).
3. Why is it unsafe to combine two NSAIDs?
It provides no additional analgesic ceiling benefit but synergistically increases the risk of severe toxicity, including massive GI bleeding, acute renal failure, and cardiovascular events.
4. When may a patient appropriately begin at the strong-opioid step?
In cases of acute severe trauma, myocardial infarction, acute surgical abdomen, or severe established cancer/palliative pain where weaker drugs will clearly be insufficient.
5. Name four measures that should accompany the initiation of a strong opioid.
1) Co-prescription of a stimulant laxative. 2) Prescription of a PRN rescue dose for breakthrough pain. 3) Anti-emetic prescription for initial nausea. 4) Clinical monitoring of respiratory rate and sedation level.
6. Why is Morphine dangerous in severe renal failure, and what is the preferred alternative?
Morphine is metabolized to Morphine-6-glucuronide (M6G), an active, potent metabolite that is cleared by the kidneys. In renal failure, M6G accumulates, causing fatal, prolonged respiratory depression. Fentanyl or Buprenorphine (which have no active renally cleared metabolites) are preferred.
