A number of people have been taken ill after taking a blue, cubed-shaped pill in Blackpool and Wyre.
Police are warning that the pills might have been sold as ecstasy, but could be either another unknown substance or an extremely high dose of ecstasy.
A number of people have become ill after taking the pills, with symptoms including sickness and vomiting.
None of the people are in a life-threatening condition.
Police are investigating the source of the pills and tests are being carried out to analyse its content.
People have reported becoming unwell after taking the drug in the Blackpool and Wyre areas, but police fear that the pills could be circulating throughout Lancashire.
Insp Mark Douglas, of West Police said: "We are looking into reports of a small number of people who suffered adverse effects after taking what they may have believed to be ecstasy.
"Our advice would be for anyone who has taken a tablet like this to seek immediate medical attention if they start to feel unwell.
"If anyone has any of these tablets and has not yet taken them they should dispose of them safely by taking them to a police station, hospital or pharmacy.
"As they are cubed shaped they could look like sweets to a child so we are especially concerned.
"There is no safe way of taking drugs, and no way of knowing exactly what you are putting into your body and whether it is safe."
Anyone with information about the blue ‘ecstasy’ tablets can call 101, quoting log 0535 of January 14.
Alternatively, you can contact Crimestoppers anonymously on 0800 555 111.