What is Pain & What Do Analgesics Do?
- Pain is the body’s way of saying something is wrong — injury, inflammation, nerve damage, etc.
- Analgesics (also called painkillers) are medicines that help reduce or remove pain.
- Different kinds of pain (e.g. pain from inflammation, from nerves, from surgery) often respond differently to different painkillers.
Main Types of Analgesics
Analgesics can be grouped broadly into three categories:
- Non‑opioid analgesics (also called “simple analgesics”)
- Opioid analgesics
- Adjuvant analgesics (also called co‑analgesics or auxiliary pain medicines)
We’ll go through each, how they work, their pros/cons, and when they’re used.
1. Non‑Opioid Analgesics (Simple Painkillers)
These are typically used for mild to moderate pain. They usually have less risk of serious dependence or addiction than opioids.
Subtypes
- NSAIDs (Non‑Steroidal Anti‑Inflammatory Drugs)
- Acetaminophen (paracetamol)
- Topical analgesics
- Sometimes other less common ones (e.g. metamizole) are used in some places.
How They Work
- NSAIDs reduce chemicals called prostaglandins, which are part of the body’s inflammation process. By blocking enzymes called cyclooxygenase (COX), NSAIDs lower inflammation, reduce pain, and lower fever.
- Acetaminophen (paracetamol) works mainly in the brain (central nervous system) to reduce pain and fever. It doesn’t do much to reduce inflammation.
- Topical analgesics are applied to the surface of the skin (creams, gels, patches). They act locally (near where they are applied). Examples include topical NSAIDs or creams like capsaicin.
Examples
- NSAIDs: ibuprofen, naproxen, diclofenac, celecoxib, aspirin.
- Acetaminophen / paracetamol.
- Topical forms: diclofenac gel; capsaicin patches or creams.
Pros & Cons
Pros:
- Good for many common kinds of pain: headaches, muscle aches, mild arthritis, fever.
- Lower risk vs. opioids for things like addiction or severe sedation.
- Some NSAIDs also reduce inflammation and swelling. Good for injuries, joint pain etc.
Cons / Risks:
- NSAIDs can irritate the stomach, cause ulcers, increase risk of bleeding. Cause kidney problems if used long term, especially in people with kidney disease.
- Acetaminophen overdose can damage the liver.
- Some NSAIDs increase risk of cardiovascular problems (heart attack, stroke) especially with long term use.
- Some patients can’t take certain NSAIDs (e.g. because of gut issues, kidney problems, or certain heart conditions).
When They Are Used
- First choice for mild to moderate pain.
- Whenever inflammation (swelling, redness) is part of the pain.
- For fever reduction.
- In many situations, combining non-opioids with other analgesics (e.g. weak opioids) is helpful.
2. Opioid Analgesics
These are stronger painkillers. Used for moderate to severe pain, or when non‑opioids don’t work enough.
How They Work
- They act on opioid receptors in the brain, spinal cord, and other parts of body. There are different types of opioid receptors (mu [μ], kappa [κ], delta etc.).
- The binding leads to less transmission of pain signals and changes in how the brain perceives pain (so even if the pain signal is there, the brain reacts less).
Subtypes
- Strong/full opioids: e.g. morphine, oxycodone, hydromorphone, fentanyl, tapentadol.
- Weak opioids: e.g. codeine, tramadol, dihydrocodeine. These are less powerful and often used when pain is moderate and other painkillers aren’t enough by themselves.
- Some opioids also have mixed or partial agonist/antagonist actions — meaning they may activate some receptors and block others. These can have different risk profiles.
Examples
- Strong: Morphine, Oxycodone, Fentanyl, Hydromorphone.
- Weak: Codeine, Tramadol, sometimes weak doses or combinations with non-opioids.
Pros & Cons
Pros:
- Very effective for severe pain (surgery, cancer pain, major injury etc.).
- Can give relief when nothing else works enough.
Cons / Risks:
- Risk of dependence, addiction.
- Side effects: sedation, drowsiness; respiratory depression (breathing slows and may drop dangerously); nausea, vomiting; constipation.
- Tolerance: over time, higher doses may be needed.
When They Are Used
- Moderate to severe pain (post-surgery, cancer, severe trauma) when non-opioids are not enough.
- Sometimes used short‑term to avoid long‑term risks.
- Often combined with non‑opioid analgesics (multimodal pain relief) to reduce needed opioid dose.
3. Adjuvant Analgesics (Co‑analgesics)
These are drugs whose main purpose is not pain relief, but they help relieve certain types of pain, especially when other analgesics aren’t enough. Good especially for neuropathic pain (nerve pain), or special situations.
Types & How They Help
- Antidepressants (e.g. tricyclics like amitriptyline; SNRIs like duloxetine) — they can change levels of neurotransmitters (serotonin, norepinephrine) that influence pain perception.
- Anticonvulsants / anti‑epileptics (e.g. gabapentin, pregabalin, carbamazepine) — they calm down nerve excitability, helpful in nerve pain (like in shingles, diabetic neuropathy).
- Local anesthetics — numb a specific area (e.g. lidocaine patches) to block pain signals.
- NMDA receptor antagonists (e.g. ketamine) — used sometimes in severe pain, or when opioids are not enough or cause unwanted side effects.
- Corticosteroids (e.g. dexamethasone, prednisolone) — reduce inflammation strongly; used in specific situations (e.g. swelling of tissues pressing nerves, cancer pain).
- Muscle relaxants, spasmolytics — when pain includes muscle spasm.
Pros & Cons
Pros:
- Can help types of pain that non‑opioids/opioids struggle with (especially nerve pain).
- Sometimes reduce the needed dose of opioids or NSAIDs (so fewer side effects).
Cons / Risks:
- They also have side effects (e.g. sedation, dizziness, risk of interactions).
- Some require careful monitoring, dosage adjustments.
- Some are not fast‑acting and may take days/weeks to show full effect (especially antidepressants / anticonvulsants).
When They Are Used
- Neuropathic pain (burning, tingling, nerve injuries).
- Cancer pain, or pain from tumors / metastases where swelling or pressure is involved.
- When regular analgesics alone don’t give enough relief.
- Often combined with non‑opioids or opioids (multimodal analgesia).
Mechanisms: Where & How They Work
It helps to understand where in the pain pathway different analgesics work. Pain signals travel from the site of injury → up through nerves → spinal cord → brain.
- Non‑opioids usually block or reduce pain at the site of injury (inflammation) or block the chemicals that cause pain.
- Opioids mainly act in the spinal cord and brain, changing how pain is felt.
- Adjuvants often target nerve excitability or brain chemistry modifying how pain is processed or how the body reacts to pain.
Special Considerations: Safety, Dosing, Choosing the Right Analgesic
Here are important things to keep in mind.
- Dose & duration: Higher doses or long‑term use increase risk of side effects. Always use the lowest dose that works for the needed time.
- Patient factors:
- Kidney/liver function: Drugs like NSAIDs or acetaminophen can cause harm if these organs are already impaired.
- Age: Elderly people are more sensitive to side effects.
- Pregnancy/lactation: Some analgesics are safer than others.
- Other health problems: stomach ulcers, heart disease, breathing problems.
- Interactions: Some analgesics interact with other medicines. For example, combining multiple medicines that slow breathing or many sedatives. Or overlapping toxicities (e.g. liver damage if many drugs metabolized by liver etc.).
- Risk of dependence for opioids: Strong opioids can lead to dependence, addiction. Even weak opioids carry risks. Use carefully.
- Overdose risks: Especially with acetaminophen (liver), opioids (respiratory depression), NSAIDs (bleeding, kidney failure).
- Effectiveness vs side effects: Sometimes a slightly less effective drug with fewer risks is a better choice, especially for chronic pain.
- Multimodal analgesia: Using more than one type together (non‑opioid + adjuvant + maybe opioid) can give better pain relief with fewer side effects.
Putting It All Together: How They Are Used in Practice
Here’s a simplified “ladder” model to decide what to use:
- Step 1: Non‑opioids for mild pain (like acetaminophen, NSAIDs)
- Step 2: If pain is more severe or doesn’t respond, add or switch to weak opioids plus non‑opioids
- Step 3: For severe pain, strong opioids (often with non‑opioids and adjuvants)
Also, for certain kinds of pain (e.g. nerve pain, cancer pain) certain adjuvants are used earlier.
Summary Chart
| Type | Strength / When Used | Examples | Main Risks |
|---|---|---|---|
| Non‑opioids | Mild‑moderate pain; inflammation; fever | NSAIDs (ibuprofen, naproxen, diclofenac), acetaminophen, topical agents | GI upset, bleeding (NSAIDs); liver damage (acetaminophen) |
| Weak Opioids | Moderate pain when non‑opioids alone not enough | Codeine, tramadol etc. | Addiction, nausea, constipation, respiratory risk |
| Strong Opioids | Severe pain, acute/chronic (cancer etc.) | Morphine, oxycodone, fentanyl etc. | High risk of dependence, respiratory depression, sedation |
| Adjuvants | Nerve pain, pain with special features; boost effect | Antidepressants, anticonvulsants, steroids, NMDA antagonists | Side effects vary (e.g. sedation, mood changes, interactions) |
Sources
- “Pharmacology of non‑opioid analgesics” (PubMed) PubMed
- “Pharmacological Methods of Pain Management: Narrative Review of Medication Used” NCBI
- “Basic pharmacology of non‑opioid analgesics” PubMed
- “Opioid and non‑opioid analgesics” PubMed
- “Weak opioid analgesics: codeine, dihydrocodeine and tramadol” etc. PubMed
- “Medications for Chronic Pain—Opioid Analgesics” MedCentral
- “Adjuvant analgesics in cancer pain treatment” United Nations Office on Drugs and Crime+1
