Wiltshire Police have tweeted that heroin of a dangerous level of purity may be being sold in the Chippenham area.
A spokesman added: “Wiltshire Police has received some reports of a high purity of heroin being sold in and around the Chippenham area.
"We are working with our partner agencies to assess this information but would always urge members of the public to never take illegal drugs.
"If you have, and you start showing signs of side effects, please dial 999 immediately and seek medical assistance.”
Anyone with information can call police on 101 or Crimestoppers on 0800 555 111 where information may be left anonymously if preferred.