In the Lab: How do lateral flow tests detect drugs of abuse?

Lateral Flow Tests (LFTs) are widely used in workplace, clinical and forensic settings to detect drug use, but drug detection works a little differently compared to healthcare testing.

1. Antibody-antigen binding – a size difference

• Healthcare markers like hCG (pregnancy hormone) are large proteins with many binding sites. They can be detected using “sandwich” assays, where antibodies bind at multiple points
• Drugs like cocaine or cannabis metabolites are much smaller, with only a single binding site. This means they require “competitive assays” – the absence of a test line actually signals a positive result.

2. Beyond the parent drug – detecting metabolites

Many drugs don’t remain in their original form in the body. For example, cannabis produces active and inactive metabolites such as 11-OH-THC and THC-COOH. LFTs are designed to detect both drugs and their breakdown products, ensuring accurate detection windows.

3. Why GHB is different

Unlike other drugs, GHB is a naturally occurring neurotransmitter in the body, so antibodies can’t be used to detect it. Instead, enzymatic reactions create colour changes, but these tests are more error-prone, have shorter shelf lives, and require controlled conditions.

4. Urine vs. saliva testing

• Urine detects mainly metabolites and gives a longer history (2–3 days)
• Saliva captures parent drugs, showing more recent use (<48 hours)
• Saliva tests reduce the risk of sample adulteration and are easier to supervise, making them well suited for workplace and roadside testing

The bottom line

Drugs of abuse testing isn’t one-size-fits-all. Whether testing urine, saliva or even drinks, the science behind each method is tailored to deliver reliable results in the right context.