In December 2004, it was announced that a new blood/serum test for psilocin had been verified to work. Psilocin is present in most psilocybin mushrooms and also an active metabolite of psilocybin.

According to a paper by Albers, Kohler et al published in 2004, the new test is highly selective and does not cross react with other common psychoactive drugs. Immunoassays are created using a technique which elicits an immune reaction in an animal so that its immune system creates an anti-body that is specific to the target chemical. The 'immunogens' bind to the chemical (in this case psilocin) and is then modified itself to be easily detected.

Immunoassays, once fully developed, are a cheap and simple way to detect very low quantities of substances in other liquids (such as blood, urine, etc). According to the paper: "The antisera showed a specific reaction with psilocin," test results indicated. "The cross-reactivity of structurally related endogenous substances like serotonin, tryptophan and tyrosine was below 0.01%... Also common drugs of abuse (Delta9-tetrahydrocannabinol, cocaine, morphine, amphetamine) showed negligible cross-reactivity (0.01%-2%)... Only tricyclic neuroleptics with a (dimethylamino)ethyl side-chain showed some cross-reactivity (20%)."

The authors conclude:

For the first time a specific immunoassay for the detection of the hallucinogen psilocin in body fluids is described. The RIA procedure is a specific immunological method for the determination of psilocin in serum or blood samples. Only short sample pre-treatment was needed and an estimation of the amount of psilocin is possible. The main advantage is the possibility to analyse whole blood samples. [ Albers et al, Dec 2004]

Although it is too soon for simple field tests made from this technology to be available, if there is a market for testing for psilocin, new products may be available in the next couple years.