Wiki of Painkiller’s type and how to use it for you by WHO

Do you see Wiki of Painkiller’s type and how to use it for you by WHO ? Pain is one of the most common symptoms displayed in both inpatients and outpatients. In case of pain, an appropriate use of painkillers will provide patients with effective treatment for their illness, improve their state of health, as well as enhance their adherence to treatment given by doctors.

Currently, painkillers are ubiquitous, so it’s not hard to find them at drugstores and on the internet. In fact, the common painkillers seem to be simply used that a lot of people just buy and take them in an arbitrary way. However, if you make a wrong choice of painkillers, your health will be negatively affected. So, in this post, we would like to equip you with types of painkillers and what to note when taking painkillers.

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According to WHO, based on medicinal effects, painkillers are categorized into 3 groups:

Type I: Peripheral analgesics, including non-opioid medicines, such as: Paracetamol, Acid Acetylsalicylic (Aspirin), Non-steroidal Anti-Inflammatory Drugs (NSAIDs), etc. These painkillers are used to alleviate slight and moderate pains.

Type II: Weak-opioid analgesics, such as code-ine, tramadol. They are used for moderate pains in combination with peripheral analgesics.

Type III: Strong opioids, such as morphine. In case of severe and unbearable pains,  a dose of strong opioids will be administered to the patients. In fact, the strong opioid analgesics are used when painkillers type I and type II take no effect.

Now, let’s dig deeper into each type of painkillers.

Painkillers type I:

Most painkillers type I (Paracetamol, Aspirin, NSAIDs) are well-tolerated. They cause no physical and psychological dependence to the patients. In reality, they are effective at alleviating slight-to-moderate pains. During the use of these painkillers, however, you should be careful to avoid potential unwanted effects. Let’s look at each specific type-1 painkiller below:

1. Paracetamol

Paracetamol is a popular painkiller for slight pains and fevers. Thanks to the balance between benefits and risks, they are regarded as the basic painkiller that can be used for both adults and children. Here are an table of standard Paracetamol doses:

Paracetamol has analgesic effects through the peripheral and central mechanism. They are often taken in combination with type-2 painkillers – code-ine Phosphate, exerting superior and more long-lasting analgesic effect compared to the single use of each drug.

Paracetamol is not recommended for inflammatory pain since it takes almost no anti-inflammatory effect. In a few rare cases, it causes allergies on the skin and thrombocytopenia.

There are two main contraindications to paracetamol:

  • Hypersensitivity to the drug and liver failure. However, compared to NSAIDs and other analgesics, Paracetamol has fewer contraindications and therefore is quite safe to use.

The overdose of Paracetamol can cause paracetamol poisoning: 10g/dose for adults and 150mg/kg of weight for children. If the patients, especially the elderly and those with poor liver function, use excess doses of Paracetamol for a long time, it may lead to even worse consequences like liver damage. The reason why Paracetamol may cause poisoning is that it is converted mainly in your liver. In particular, the main metabolic pathway for Paracetamol is sulfate and glucuronic.

Overdose symptoms: nausea and stomachache within 24 hours. Even worse, if liver enzyme elevates, it can lead to hepatic necrosis and coma.

Solutions: In case of paracetamol overdose and poisoning, the patient must be urgently taken to the hospital as soon as possible. They will be prescribed antidotes like N-acetylcysteine.

For the pregnant and breast-feeding, they must follow their doctors’ instructions to use Paracetamol with recommended doses and in a short period.


As a popular painkiller like Paracetamol, Aspirin is used to reduce fevers, inflammation,  and pain. Especially, Aspirin can treat rheumatism or  painful arthritis.



  • Hypersensitivity to Aspirin
  • Asthma,
  • Women in trimesters of pregnancy, breast-feeding women,
  • Coagulation disorders,
  • Stomach and duodenal ulcers,
  • Impaired kidney and liver function

Unexpected side-effects:

  • On the digestive system: stomachache, gastrointestinal bleeding (vomiting blood, or rectal bleeding)
  • On the nervous system: headache, dizziness, tinnitus, etc.
  • Others: urticaria, constriction responses, etc.

Interactions with other drugs:

  • Use in no combination with: anticoagulants, methotrexate, other NSAIDs, heparin.

Non-salicylate NSAIDs:

High doses of Non-salicylate NSAIDs can be used to reduce and control inflammation, while lower doses can ease slight-to-moderate pains like: toothache, headache, migraine, mild concussion, otolaryngological pains, etc.

Non-salicylate NSAIDs can combine with stronger painkillers to alleviate pains caused by cancer. Standard dose of Non-salicylate NSAIDs is dependent on different ages, physiological status (e.g: pregnant), and pain intensity.


  • Hypersensitivity
  • Stomach and duodenal ulcers,
  • Impaired kidney and liver function
  • Inflammatory Bowel Disease (IBD)
  • Dehydration
  • Malnutrition
  • Children under 15
  • Pregnant (From the 6th month) and breast-feeding

Unexpected effects:

  • On the digestive system: epigastralgia, indigestion, nausea, etc.
  • On the kidney: acute renal failure (for high-risk groups: those with cirrhosis, chronic kidney diseases, heart failure, the elderly above 75)
  • On the respiratory system: asthma, acute respiratory failure, bronchospasm, allergies.
  • On the blood system: anemia, low white blood cell count, thrombocytopenia, etc.
  • On the liver: hepatitis, jaundice.

Drug interactions:

  • No combination with: other NSAIDs, Aspirin, oral anticoagulants, unfractionated heparin, lithium, methotrexat (>20mg/week), pemetrexed (for those with serious kidney failure).
  • Careful use with: ciclosporin, tacrolimus, enzyme inhibitors, diuretics, angiotensin receptor blocker II (sartan), methotrexat (<= 20mg/week).

Note: Non-steroidal painkillers can raise the level of potassium in blood.

3. Floctafenine

Floctafenine is a painkiller taken by mouth in a 200mg tablet form. A standard dose of Floctafenine is 1 tablet at a time and no more than 4 tablets per day. The minimum interval between two doses of Floctafenine is from 4 to 6 hours.

Floctafenine may trigger some very rare but serious adverse reactions that require immediate discontinuation. In fact, there have been some cases of reactions to Flotafenine at various degrees: allergic or shocked.

4. Nefopam

Nefopam is a centrally-acting painkiller that impacts upon the brain and spinal cord to deaden the pain. If you are prescribed Nefopam, you will take it intravenously or intramuscularly. Nefopam is often administered to the patients who suffer from acute and sudden pains as well as post-op patients. It’s not used to help reduce the inflammation or fevers.

This drug is contraindicated in patients with a medical history of seizure disorders or a high risk of urinary retention (related to prostate problems), or coronary artery disease. In serious cases, it can cause nausea and vomiting.

Painkillers type II:

The analgesic effect of painkillers type II is similar to Morphine but lower.  They are weak opioids and often used in combination with Paracetamol. They are suitable for treating moderate-to-severe pains. Your doctor will prescribe you these drugs in cases as follows:

  • Painkillers type I bring about no effect
  • Post-op and post-concussion pain.
  • After injecting Morphine.

1. code-ine

It is a kind of weak opioid that can quickly convert into Morphine at a rate of 10%. Its effect can last for a long time and be compared to 10% of Morphine. The dosage of code-ine should be carefully considered to ensure tolerance.

Typical dosage:

  • For adults: 30-60mg within 4-6 hours.
  • For children: 1-3mg/kg/day in form of syrup, no more than 6mg/kg/day.
  • Overdose: overdose can cause the patients to go into convulsions.


  • Hypersensitivity to code-ine,
  • Cough with sputum,
  • Drug addiction,
  • opioid dependence,
  • Respiratory failure,
  • Asthma
  • Serious heart failure
  • The pregnant and breast-feeding

Unwanted effects:

  • Constipation
  • Sleepiness
  • Dizziness
  • Nausea and vomiting
  • Bronchospasm
  • Allergy
  • Respiratory failure
  • Drug withdrawal effect

Interactions with other drugs: code-ine should not be used with opioid agonists and antagonists like Nalbuphine, Buprenorphine, Pentazocine. Besides, you are not recommended using code-ine when drinking alcohol. In addition, avoid using code-ine in combination with hypnotics like Benzodiazepine, Barbiturate or other central nervous system depressants.

2. Tramadol:

Tramadol is a painkiller used to help dull moderate-to-severe pains. It has a less strong impact on your digestive and respiratory system than Morphine. Its effect can be compared to 1/10 – ⅙ of Morphine’s.

Dosage of Tramadol depends on the level of pain or the patients’ health condition:

  • Tramadol as tablets: 100mg for severe pains and 80-100mg for chronic pains. You should not take Tramadol more than 400mg/24 hours.
  • Tramadol via injection: slow injection (from 2 to 3 minutes) or infusion into intravenous fluids.
  • For people above 75: need to lengthen the interval between two doses (9h)
  • For those with liver failure: reduce the dose by a half and double the interval between two doses (12h).
  • For those with kidney failure: double the interval between two doses (12h). It is not recommended for the patient with the renal clearance under 10ml/minute.


  • Hypersensitivity to Tramadol and Opioids.
  • Respiratory Failure
  • Serious hepatic failure
  • People under 15
  • The breast-feeding
  • Seizure

The use of Tramadol needs to be considered based on the balance of benefits and risks.

Unexpected effects:

  • Neurological disorder (especially in the elderly)
  • Confusion
  • Illusion
  • Paranoia
  • Convulsion


  • Common side-effects: nausea, sleepiness, headache, dizziness, tiredness, dry mouth, constipation.
  • Rare side-effects: epigastralgia, diminished vision, heart disorders (fast heart rate, low blood pressure, hypertension, palpitations)
  • Very rare side-effects: allergies, angioedema, bronchospasm, urinary disorders (uncomfortable urination or urinary retention), drug dependence and withdrawal effect, hysterics, anxiety, stress, tremble, elevated liver enzyme.

Interactions with other drugs:

  • No use in combination with: opioid agonists and antagonists (buprenorphine, nalbuphine, pentazocine), alcohol, carbamazepine, naltrexone.
  • Careful use with: painkillers like Morphine, selective serotonin reuptake inhibitors, venlafaxine, tricyclic antidepressants, tranquilisers.

For the pregnant and breast-feeding, they must use Tramadol with the monitor and advice of doctors. They had better avoid using Tramadol in the first trimester of pregnancy.

Painkillers type III

The painkillers type III are strong opioids that can cause addiction and respiratory failure. That’s why they must be used cautiously and with doctors’ prescription only.

They are categorized into 3 types:

  • Agonists, like Morphine
  • Partial agonists, such as Bunerophine
  • Antagonists, like Nalbuphine.

Notes: never use 3 aforementioned types in combination with each other due to their antagonistic effects.

1. Morphine

Although Morphine is not the strongest painkillers, it is regarded as a reference drug. It is best used for persistent and severe pains, especially pains caused by cancer. Unlike what people are afraid of, Morphine will cause no illusion or dependence if it is used properly.

Typical dosage of Morphine is 60mg/day at the beginning. After 4 hours since the starting dose, the dose will be increased by 30-50%. During the interval between two doses, a preventive dose can be added if the patient suffers from unbearable pains.


  • Hypersensitivity to Morphine
  • Children under 6
  • Respiratory failure
  • Decompensated Maple Syrup Urine Disease (MSUD)
  • Serious liver failure
  • Chronic disease (traumatic brain injury, increased intracranial pressure, pressure-controlled ventilation.
  • Uncontrolled seizure
  • The breast-feeding

Adverse reactions and unwanted effects:

  • Inevitable repeated constipation
  • Sleepiness
  • Uncomfortable urination
  • Perspiration
  • Itchiness

Even worse, overdose of Morphine can cause:

  • Euphoria
  • Nightmare
  • Confusion (for the elderly)
  • Illusion
  • Respiratory failure
  • Urinary obstruction and retention (often related to prostate cancer)
  • Morphine withdrawal effect
  • Uncontrolled convulsions (with a very quick use of Morphine)

Interactions with other drugs: Morphine is a strong painkiller that has a direct impact upon the central nervous system, so do not use it with other drugs of the same type (Tranquilizers, Benzodiazepine, Baclofen, Thalidomide, Methyldopa, Histamine H1, Bprenorphine, Nalbuphine, Fentanyl, Naltrexone, Rifampicin, other opioid painkillers (Alfentanil, code-ine, Dextromoramide, Dihydrocode-ine, Fentanyl, Oxycodone, Phenoperidine, Remifentanil, Sufentanil, Tramadol), morphine-like antitussives (Dextromethorphan, Noscapine, Pholcodine), Barbiturat, Benzodiazepin).

2. Fentanyl

It is a morphine-like painkillers that has strong, quick, and long-lasting analgesic effects. In fact, its effect is 100 times stronger than Morphine’s. It is often administered to chronic and severe pains that cannot be treated by other opioids.

Using Fentanyl requires taking a consideration into previous opioid treatment regimes. There is no typical dose of Fentanyl, but it depends on the level of drug dependence, the patient’s health condition, and the severity of their diseases.


  • Hypersensitivity
  • Acute post-op pains
  • Neurological disorders
  • No previous use of strong painkillers

Unwanted side-effects:

  • On the heart: fast/slow heart rate, arrhythmia
  • On the nervous system: headache, feeling dizzy
  • On the skin: itchiness, perspiration.
  • On the psychology: loss of appetite, depression, stress
  • On the digestive system: vomiting, constipation, dry mouth, digestive disorders.

Interactions with other drugs: similar to Morphine.


  • Never use Fentanyl for children who never take opioids.
  • Fentanyl’s biological half-life is long-lasting in aged patients.
  • The pregnant and breast-feeding should be careful when using Fentanyl. They had better avoid using it.

3. Oxycodone

It is also an opioid agonist like Morphine. It can be used to reduce pains, anxiety, cough and act as a tranquilizer. Oxycodone is taken every 4-6 hours when the patient suffers from agonizing pains. Its effect can last about 12 hours.

Typical dosage of Oxycodone:

  • For adults (above 18): 5mg – 15mg in every 4-6hours as needed.
  • For children: Oxycodone is moderately unsafe to children, so they are not recommended using it.
  • For those with kidney and liver failure: Be careful to use it because the drug can be slowly processed.

Unwanted side-effects:

  • slowed breathing,
  • yawning, diarrhea,
  • teary eye,
  • runny nose.

Interactions with other drugs:

  • It can become dangerous to your health if you take Oxycodone with Anesthesia drugs (butorphanol, nalbuphine, pentazocine).
  • Its effects can be minimized (less effective)  in combined use with Antibiotics (Rifampin, Rifabutin, Rifapentine) and Anticonvulsants (carbamazepine, Phenytoin).
  • Its side-effects can be increased when used with: Antifungal (Voriconazole, Ketoconazole) and Antibiotics (Erythromycin, Clarithromycin).
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