Two Toowoomba trainers have been stood down after a drug and alcohol screening operation by Queensland Racing Integrity Commission officers at morning track work.

About a dozen work riders, jockeys and trainers have been stood down or suspended around the state following snap raids by integrity officers in recent months.

In Toowoomba, the two trainers were stood down after screening positive in preliminary testing for prohibited substances.

A QRIC spokesperson said one trainer made admissions to drug use, while another trainer screened positive to benzodiazepines and when breath tested returned an alcohol reading in excess of the permitted .02 threshold.

Both were stood down pending confirmatory analysis.

It is policy not to name those stood down until the positives are confirmed by a second test and those involved front stewards.

Integrity officers have also conducted a sampling operation at Ipswich after receiving information a rider had allegedly avoided testing last week.

One work rider screened positive to methamphetamine and amphetamine and a second rider tested last week screened positive to tetrahydrocannabinol.

Both were stood down until the results of a second test are known.