The strong tranquilliser flualprazolam is being widely used in the four southernmost provinces of Thailand, officials say.

It's the first time the drug has been found in Thailand.

Dr Supakit Sirilak of the Department of Medical Sciences said on Wednesday that Regional Medical Sciences Centre 12 had analysed nimetazepam pills, or Erimin 5, listed as a psychotropic substance.

The officials found flualprazolam in the nimetazepam pills. Flualprazolam is a tranquiliser that eases anxiety and is used to treat panic and insomnia.

Nimetazepam 5mg, sold under the name Erimin 5, is banned in Thailand. However, reports said the drug has been widely used in the four southernmost provinces, especially in Narathiwat. The other three provinces are Pattani, Yala and Songkhla.

Dr Supakit added that other substances may have been mixed with nimetazepam to avoid prosecution.

Dr Supakit said flualprazolam effects will begin within 10-30 minutes and last 6-14 hours.