How Long Does Acetaminophen Stay in the Body?

Topics Covered


The medicine used for treating pain and fever is acetaminophen, also commonly known as paracetamol. The medicine is best for treating mild and moderate pain; it is also known for relieving fever in children. The medicine is usually prescribed to a person along with other medications for treating the condition. Severe pain like cancer pain or post-surgery pain is also treated with this medicine. Acetaminophen is generally taken in the form of capsules, tablets, and drops. The effect lasts from two to four hours. Although the medicine is considered safe for use under recommended dosage, it can cause serious health issues like a liver failure when taken in too high dosage. Paracetamol was discovered in the 1877 and is the most popularly used medicine for pain relief in the United States even today.

How Long Does Acetaminophen Stay in the Body?

What is Acetaminophen?

Acetaminophen is the drug commonly known as paracetamol. This drug belongs to the class of drugs known as analgesics and antipyretics. The drug is known for its efficiency in relieving pain and reducing fever when taken orally or rectally, the two common ways of putting the drug to use. Although the actual action mechanism of this drug is not yet known, it is still believed to reduce the production of prostaglandins in the brain, the chemicals which cause swelling and inflammation. Acetaminophen works to reduce fever in a person by acting on the heat-regulating point of the brain by controlling the body temperature and bringing it back to normal when the temperature of the body is elevated. It also relieves pain by elevating the pain threshold, which helps the person to not feel the pain and hence, relieves him. Acetaminophen was approved by the FDA in 1951.

What is Acetaminophen Used for?

The main use of acetaminophen is to relieve pain and reduces fever, which can also be associated with many other conditions. For example, acetaminophen is used for relieving cancer pain and post surgery pain by using it in a combination with other medications to treat the condition. Acetaminophen is also used for treating pain caused due to mild arthritis, but does not have any effect on the redness or swelling of the joint. The pain treated with acetaminophen must not be due to inflammation, which is when it will work on relieving the pain just like aspirin, not otherwise. The drug is considered safe and is most commonly used by people all over the world for relieving pain and fever, but it must be used as suggested by the physician. Taking acetaminophen in high doses or for too long might be bad for health which is why it should be taken in a dosage as recommended by the physician.

If the drug is not used as recommended, it can lead to side effects like nausea, headache, and rash. Major side effects like skin reactions, anemia, kidney damage and hypersensitivity reactions can also take place when taken in too high dosage.

How Long Does Acetaminophen Stay in your Body?

Through a number of researches to understand the highest level of acetaminophen in one’s blood and the half life of acetaminophen, it has been noticed that the level of the drug in human plasma from 30 minutes to two hours reaches to its peak when taken orally. The half duration of acetaminophen is usually from two to four hours that means the drug starts acting on our body after 30 minutes of taking the medication orally. It remains in our blood and reaches its peak in one and a half hour and the level starts to decline in the flowing two hours, making the drug effective for the first four hours. Due to this duration of acetaminophen in our body, the drug has to be taken every 4 to 6 hours to relieve pain or fever in order to get the best results.

Factors that Determine How Long Acetaminophen Stays in your System

Apart from the fact that acetaminophen usually stays in the system for up to 4 hours and in some cases up to 6 hours, there are certain factors that determine how long the drug is going to be in your system. These factors can differ from one person to another and they are:

  • Body mass of the person.
  • Age.
  • The individual’s metabolic rate of drugs which will determine the rate of acetaminophen elimination from his body.
  • Whether you are a chronic or mild user of the drug.

There are other factors that could determine how long the drug will stay in your system like the level of glutathione in your body which, when low, can tend to keep acetaminophen longer in your system. Glutathione is important for the elimination of acetaminophen from your system as the process of elimination requires reactions like sulfation and sulfation is dependent on the level of glutathione in your body.

Different Tests that Determine the Presence of Acetaminophen in the Body

There are several ways to test the presence of acetaminophen in your body. The presence of this drug can be detected in urine, hair, saliva, blood, and fingernails. The acetaminophen blood test helps in determining the level of acetaminophen in the blood. The test is usually conducted to diagnose an overdose and check if there is a risk of liver damage. Through blood tests, the treatment required can also be determined. There are certain situations when an acetaminophen blood test is performed like:

  • If there has been an overdose or so is suspected, the blood sample is collected from the person’s body and sent for checking acetaminophen levels every four to six hours.
  • Sometimes, the sample can be taken early and the results might not show the exact levels of acetaminophen in the person’s blood which would require drawing samples again for testing.

The levels of acetaminophen in an individual’s body can also be detected through urine screening, where the urine samples taken from the person’s body helps to detect the levels of acetaminophen with good accuracy and check if there is an overdose.

Acetaminophen can be detected in the system of an individual for as long as the drug is active in the person’s body. Generally, then drug stays active in our system for 4 to 6 hours of taking the drug. But, in case of overdose, the body can even take more than twelve hours to eliminate half the amount. Thus, in cases of overdose, acetaminophen can be detected through various lab tests by taking samples of hair, fingernails, blood, urine, and saliva of the person from one to seventy hours of taking the drug.

Can Acetaminophen be Detected via Drug Tests?

The drug tests like 5-panel drug tests are tests for detecting certain narcotic analgesics like morphine, codeine, oxycodone, etc. and acetaminophen is not among them, which is why this drug cannot be detected with a drug test. Previously, the drug tests would show a false or positive result on detecting acetaminophen in the person’s system, when tested for narcotics. But, with the advancement in technology today, the labs can differentiate between narcotics and acetaminophen. Thus, acetaminophen cannot be detected via drug tests.

Drug Tests that Determine the Presence of Acetaminophen in the Body

There are two types of tests that can detect the presence of acetaminophen in the body they are:

  • Blood analysis
  • Urine analysis

When is Acetaminophen Tests Needed?

Acetaminophen overdose is one common reason for liver damages which can be pretty serious and life-risking if not diagnosed and treated at the right time. For adults, a dosage of not more than 4,000 mg of acetaminophen must be taken within 24 hours and 3,000 mg is the maximum you should take each day when you are using this drug for quite some weeks. A dosage of 7,000 mg or more is considered an overdose and dangerous. If your doctor suspect there has been an overdose of the drug, then he or she shall ask you to take the acetaminophen test to diagnose and see if you need to undergo any treatment for liver damage. There are 4 stages of overdosage. In the first stage, certain symptoms might arise within 24 hours or less from overdosing which includes:

  • Loss of appetite.
  • Stomach cramps.
  • Vomiting.
  • Nausea.
  • Fatigue.

The above-mentioned symptoms might go away within 72 hours, but if you find the signs and symptoms getting worse then you are in stage 2, the symptoms you might experience then are:

  • Frequent urination.
  • Liver gets enlarged.
  • Pain in the upper abdomen on the right side.

The symptoms will get worse from day 3 or day 4 and along with the symptoms from stage 1, you will experience more symptoms like:

  • Bleeding
  • Confusion
  • Jaundice

You might survive stage 3 and get rid of the above-mentioned symptoms between day 4 and day 7. If you reach this stage, you will recover, but some people still have liver or kidney damage upon reaching this stage. On noticing these symptoms which could be a result of overdosing or could also be a result of the build of this medicine in the body from taking it too often, the doctor will order the acetaminophen tests to be taken for further analysis and treatment.


When you realize that you are seeing signs and symptoms of acetaminophen overdose, do not try to fix your problem yourself with other medications. Instead, you must go and seek help from a physician right away. With prompt treatment, serious liver damage can be prevented which is why it is important to understand the symptoms of acetaminophen overdose and also use the drug very safely by taking the recommended dosage and not more than that.

Posts You May Like:

You May Also Like