Three Preston teenagers have been arrested on suspicion of supplying a “potentially lethal” drug.
Police have issued a warning after tablets being sold as Valium are a much stronger drug.
A number of young people aged 14-19 in Preston have been admitted to hospital after taking the drug.
They suffered from blue lips, lethargy, drowsiness and chest pains.
Officers say the drugs are potentially lethal as they are far stronger than valium.
They have been offered for sale in Brookfield and Fulwood.
A 15,16 and 19-year-old have been arrested on suspicion of being concerned in the supply of Class C drugs.
Detective Inspector Warren Atkinson said: “The main concern is that these tablets are being sold illicitly as Valium as opposed to what they really are which is Phenazepam. This is very worrying as these tablets are far stronger than Valium and the effects last much longer.
“So far, four young people have needed hospital treatment as a result of taking this drug and we do not want there to be any more casualties.
“The advice is for anyone who has purchased similar tablets to seek immediate medical attention if they notice any different symptoms or start to feel unwell.
“What makes this substance different is that it can take up to two to three hours to ‘kick in’ and the effects can last around 60 hours. Because it takes time to ‘kick in’ people have been taking more tablets, initially thinking there has been no effect, causing a greater negative effect.
“Lancashire Constabulary takes a proactive response to tackling the issue of drugs in the county. We are particularly keen to recover the outstanding tablets, as they pose such a danger to anyone who takes them. We would urge anyone who has any information about illegal drug related activity to contact us.”
Anybody with any information can contact police on 101 or Crimestoppers anonymously on 0800 555 111 or on-line at Crimestoppers-uk.org