The question of how long drugs stay in your system is not an easy one to answer.

First, there are thousands of drugs available for human consumption, both legal and illicit, and they all stay in your system for different amounts of time; and,

Second, there are other factors that determine how long a drug lasts, including your metabolism, body mass, hydration, how much of the drug you took, and how often you take it.

While you can find lists that show you how long certain drugs stay in your system, it’s impossible to provide that information for every drug in existence. However, what we can do is talk about the drug half-life, which is influenced by how your body processes different types of drugs — which can help you understand why certain drugs linger longer than others.

What is the Drug Half-Life?

The drug half-life is the amount of time it takes for half the dose of a given drug to clear your system.

For example, if you take 40 mg of a drug as a four-hour half-life, then it will take:

Four hours for 20 mg to clear your system;

Four more hours for 10 mg to clear;

Four more hours for 5 mg to clear;

Four more hours for 2.5 mg to clear;

Four more hours for .75 mg to clear, and so on.

This means that a drug with a four-hour half-life could remain in your system for 20 hours or more. However, as the dosage dwindles, so do the effects of the drug. Which means the drug could still be in your system, even if you no longer feel the effects.

Half-life is only part of the equation. There is also the way your body processes the drug that can determine how long it stays in your body. It can also influence how medications are used in drug detox and to treat certain illnesses.

How Your Body Processes Drugs and Alcohol

All drugs go through four basic stages inside your body: absorption, distribution, metabolism, and excretion.

Absorption

The absorption stage is the point at which you take the drug into your body, which can occur in several ways, such as through your mouth, through your nose, through your eyes, through your anus, or through your skin. The method by which you absorb the drug depends on how the drug is packaged.

For example, a steroid nasal spray is usually dispensed as an aerosol through your nose, while a steroid pill is usually ingested. A pain relieving patch is dispensed through your skin, while a pain-relieving liquid could be administered directly into the vein.

The way you absorb a drug can affect how well it works.

For example, the steroid nasal sprays goes straight to the treatment area, whereas the steroid pill has to go through the acid in your stomach, which can destroy some of the drug. The pain relieving patch has to make it through layers of fat beneath the skin, whereas an intravenous injection goes straight into the bloodstream. This is one of the reasons why certain absorption methods work well on some people, but not others.

Some drugs are only effective when absorbed in one way, such as insulin, which is always injected; others can be absorbed in multiple ways, such as opiate pain killers, which can be injected, administered in a patch, or ingested in liquid or pill form.

Distribution

Distribution is the process of carrying the drug to the target area in your body.

Some drugs have a very short line of distribution because they are applied directly to the affected area, like the steroid nasal spray in the example above, stomach medication ingested through the mouth, asthma medications inhaled into the lungs, topical medications applied directly to a damaged area of skin.

Other drugs have to travel through the blood stream to get to the treatment area, such as an aspirin or an IV painkiller taken for pain, an ingested for an allergy, antihistamine taken for an allergy, taken for a headache, or a nicotine patch used to curb cravings.

Drugs that are ingested into your stomach also have to pass through your intestines, and be filtered through your liver before they can reach your blood stream to be distributed to the treatment area.

It’s important to note that even when a drug is administered directly to the treatment area, it’s possible for some of it to end up in your blood stream, which is why some topical drugs can have other side effects. Because once it enters your blood stream, it can affect other areas of your body.

Several factors can influence how quickly a drug is distributed to the treatment area through your blood stream, including the concentration of proteins and fats in your blood stream, and whether or not it has to pass through the blood-brain barrier.

Metabolism

Metabolism is the process where your body breaks down the drug and transforms it into something else. Metabolism can actually occur before or after the distribution process, depending on how the drug was originally absorbed into your body.

Keep in mind that absorption can also occur in multiple ways at once.

For example, when you drink alcohol, some it is absorbed directly into your blood stream through your stomach lining, some of it is absorbed through your intestines, and some enters your blood stream through your liver.

When a drug enters your liver, the enzymes in your liver break down the drug, which alters its nature. Some drugs are designed to be dormant until the processes in the liver make them active; other drugs are designed to be active until the processes in the liver turn them off, which is another reason why some drugs can only be absorbed in certain ways.

The drug itself can also affect metabolism. If a drug, like speed, increases your rate of metabolism, it will also cause you to metabolize the drug faster. If a drug, like OxyContin, decreases your rate of metabolism, it will also cause you to metabolize the drug at a slower rate.

Excretion

Excretion is the process of the drugs leaving your body. Urination is the most common method of excretion, which is why labs use urinalysis to detect whether or not you have used certain drugs in the recent past.

You also excrete drugs through defecation, as well as through respiration and sweat.

For example, alcohol is excreted through respiration and sweat, which is how breathalyzers can detect the presence of alcohol in your blood, and why people sometimes smell like alcohol after a long night of drinking.

List of Common Drugs’ Duration in Your System

Conclusion

The drug’s natural half-life, with the method of absorption, rate of distribution, rate of metabolism, and method of excretion, all determine how long a particular drug stays in your body.

A drug like alcohol, which has a fairly short half-life, and is absorbed and excreted through multiple channels, only stay in your body for a few hours — which is a relatively short time. A drug like an anabolic steroid, which has a fairly long half-life, is are excreted and absorbed through few channels, could stay in your body for weeks or months.

If you the drug on a regular basis, then it will take even longer to clear because you will be constantly increasing the dosage, even as your body works to eliminate it.