[For Medical Professionals/Beginners🔰] A Rough Guide to Using Analgesics
First, the conclusion:
The medication changes depending on the "type" of pain.
Here is a rough classification of pain.
• Nociceptive pain (throbbing/inflammation/musculoskeletal): bruises, sprains, post-tooth extraction, joint pain, sore throat, etc.
→ Acetaminophen / NSAIDs are the mainstays
(Acetaminophen = use this if in doubt, watch out for liver damage)
(NSAIDs = strong effect, watch out for gastric ulcers/kidney damage)
• Neuropathic pain (tingling/burning/electric shock): radiating pain like sciatica, post-herpetic neuralgia, diabetic neuropathy, post-surgical numbness/pain, etc.
→ **Pregabalin, Duloxetine, TCAs etc. ("adjuvant analgesics") are the mainstays; general painkillers alone are often ineffective 
• Cancer pain (persistent pain + breakthrough pain, etc.):
→ Opioids + non-opioids + rescue medication design is the standard (including safety management) 
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1) Acetaminophen (Calonal, etc.): The "safest" option
Suitable for:
• Fever, cold-related pain, mild to moderate pain in general
• Since it is relatively gentle on the gastrointestinal tract, it is often the first choice for those where NSAIDs are a concern
Crucial points to note (just memorize these):
• For adult analgesia, the principle is dosing intervals of 4-6 hours or more, with a total daily dose of up to 4000mg (there are exceptions depending on the formulation/indication) 
• "Cold medicines/over-the-counter multi-symptom cold remedies" may also contain acetaminophen, so be careful of duplication (a typical case of exceeding the limit without knowing) 
• Liver damage risk: risk increases with large doses, continuous use, malnutrition, alcohol consumption, or existing liver disease (warnings based on the package insert) 
• **Aspirin-induced asthma (AERD)** patients may have restrictions such as "300mg or less per dose" according to the package insert, so be careful 
In a nutshell: "Start with this"
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2) NSAIDs (Loxoprofen, Ibuprofen, Diclofenac, etc.): Strong against inflammation, but with many landmines
Suitable for:
• Pain involving inflammation (sprains, arthritis, toothache, menstrual pain, etc.)
• Strong against "swollen and hot" types of pain
Common side effects (in order of importance):
• Gastrointestinal: stomach pain to ulcers/bleeding (hematemesis/black stools are red flags) 
• Renal: acute kidney injury, high potassium, edema (especially in cases of dehydration, elderly, or reduced renal function) 
• Cardiovascular: Risks such as myocardial infarction/stroke are sometimes discussed 
• Asthma: Can worsen. Especially aspirin-induced asthma
"Common but dangerous" combinations:
• ACE inhibitors/ARBs + diuretics + NSAIDs (the so-called triple whammy): risk of kidney damage skyrockets
Pregnancy •First, do not use
In a nutshell: "Strong against inflammatory pain. However, check for
stomach, kidney, pregnancy, and concomitant medications. Check these."⸻
3) COX-2 selective NSAIDs (Celecoxib, etc.): Relatively better for the stomach, but not a panacea
Features:
• While gastrointestinal damage is considered "relatively" lower, the basic stance of being cautious about cardiovascular events and using the minimum effective dose for the shortest period remains the same 
• Cannot replace aspirin (platelet effects are different) 
In a nutshell: "
Often an option for those worried about their stomach, but cardiovascular risk and long-term indiscriminate use are separate issues."⸻
4) Topical agents (patches/ointments): Seem safe, but pregnancy is a different story
• Topical agents often have fewer systemic side effects, but there have been reports of fetal ductus arteriosus constriction even with topical NSAIDs in the second trimester and beyond, so it cannot be said that "pregnancy = topical is okay" 
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5) Opioids (Tramadol to strong opioids): Effective, but 90% is "design" and "management"
When to use (roughly):
• Moderate to severe pain, cancer pain, pain insufficient with non-opioids, etc.
• However, for chronic non-cancer pain, "pre-start assessment, goal setting, and management of side effects and addiction risk" are super important (facility rules also play a role here)
Super practical points to note:
• Constipation, drowsiness, and nausea are "almost a set." Consider them with countermeasures included
• Do not lazily stack drugs of the same class because they aren't working; guidance suggests a mindset of switching or rotating to an opioid of appropriate strength 
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6) Adjuvant analgesics effective for "nerve pain": You'll get stuck if you don't know these
For neuropathic pain, increasing Loxonin often doesn't work.
Guidelines organize the efficacy of duloxetine, Ca channel α2δ ligands (pregabalin, etc.), TCAs, and opioids for each pathological condition 
Points to note (common issues):
• Drowsiness/dizziness (especially at the start/when increasing dose)
• Renal function requires dose adjustment for many drugs
• It may take some time to judge the effect (a different category from "fast-acting painkillers")
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Super rough quick reference for usage (if in doubt, look here):
• Fever, sore throat, mild pain: Start with Acetaminophen 
• Pain with strong swelling/inflammation: NSAIDs (but check stomach, kidney, pregnancy, and concomitant medications) 
• Tingling/numbness type: Consider drugs for neuropathic pain (do not stick only to general analgesics) 
• Severe pain/cancer pain: Design including "rescue medication and side effect countermeasures" along with opioids 
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Danger signs requiring detailed examination before "painkillers":
• Chest pain, paralysis, impaired consciousness, sudden severe pain, persistent severe abdominal pain
• Fever + neck stiffness, immunosuppression, severe pain during pregnancy
• Hematemesis/black stools after taking NSAIDs, shortness of breath, rapid increase in edema, clearly reduced urine output
→ These require evaluation before "choosing a drug."
In conclusion
How was it? Did you get a rough idea of how to distinguish between analgesics? Please feel free to dig deeper into any medications that caught your interest.
To be honest, what is commonly used and what is not depends on the hospital, the ward, and the doctor, so
asking your senior doctoris the fastest way.I hope to create a complete version with specific prescription examples in the future.
Thank you again!