d- & l- Methamphetamine Isomers

DL Isomers

d- & l- Methamphetamine Isomers

For most non-drug users, methamphetamine exists as a single substance, a street drug known as meth, crystal, speed, or crank. In the public eye, meth causes rotting teeth, pockmarked or scabbed skin, and erratic behavior, creating an attitude known as tweaking. All of this is generally true to some extent – meth is a potent drug that has the ability to be life-ruining for those who cannot overcome their demons – and media portrayals of meth do have some semblance of reality.

However, the average American is unaware that he or she has likely enjoyed the effects of meth a time or two in life – just not the kind of meth the news frequently paints with a colorful brush. Methamphetamine has two isomers, d-methamphetamine and l-methamphetamine. One of these is used in prescription medications and is available in street drugs, while the other is most commonly found in nasal decongestants.

Breaking Down Meth

It’s true that methamphetamine can be inherently problematic when used illicitly, but all methamphetamine is not made equal. Methamphetamine, like many other chemical structures, has more than one isomer, or a compound with the same formula that is arranged differently.

Isomers come in two distinct forms: structural isomers and stereoisomers. A structural isomer refers to the specific attachment of atoms and functional groups that make up a compound, leading to two radically different substances that are often classified differently or have different IUPAC names. Stereoisomers vary instead by orientation, or the ways in which a compound is positioned in space.

Methamphetamine’s isomers are stereoisomers, so they are arranged in the same way and have the same chemical properties but are differentiated by their effects on the body.


Dextromethamphetamine, or d-methamphetamine, is a stimulant of the central nervous system and is classified as a DEA Schedule 2 controlled drug, which means that it is easily abused and quite addictive. The street drug known as meth generally contains primarily d-methamphetamine.

D-methamphetamine is also used in prescription medications like Desoxyn. Desoxyn is a stimulant most commonly used to address ADHD, but can also be used to stimulate weight loss in overweight adults.


Levomethamphetamine, or l-methamphetamine, is methamphetamine’s second isomer. Unlike d-methamphetamine that is highly controlled and potentially addictive, l-methamphetamine is not regulated by the DEA and is found in many over-the-counter medications designed to treat nasal congestion. It can also be found in prescription drugs like Selegiline, a medication that addresses Parkinson’s disease and depression.

L-methamphetamine is considered to be generally safe and does not pose a risk to those sensitive or addicted to d-methamphetamine. However, some forms of street meth do contain l-methamphetamine, but rarely in large doses.

The Importance of Methamphetamine Isomers

D-methamphetamine and l-methamphetamine are the same in structure but quite different in use. However, this does not mean they are indistinguishable on a drug test – a fact that can cause issues for those taking drugs with l-methamphetamine legally and for health reasons. This is particularly true for those being screened for purposes that can lead to significant consequences if results are positive for controlled substances, like those on parole or who are testing for employment purposes. Standard LCMS confirmations do not distinguish between the two methamphetamine isomers, so someone with a heavy meth habit and someone with a bad cold may walk away from a drug screening with similar test results.

DL methamphetamine isomer screening can shed light on the reality of test results, helping to isolate the split, if available, between d-methamphetamine and l-methamphetamine, and in what ratios. For example, an individual taking heavy doses of nasal decongestant will test positive for 100% l-methamphetamine, while someone with a crystal meth habit will likely have results that skew strongly toward d-methamphetamine.

Due to the addictive qualities in meth, d-methamphetamine is the primary ingredient in street meth. For this reason, federal drug testing policies have determined that a specimen that contains 20% d-methamphetamine or more is considered exposure to a controlled substance, and is interpreted as “testing positive” for illegal drugs, in layman’s terms.

In a drug test, precision is critically important, both in medical and legal settings. A DL isomer test can provide clarity to a standard drug panel, helping both subjects and screeners alike to determine the true makeup of a drug sample by providing authentic, verifiable results.