Eight police officers had to be treated in hospital after being exposed to an unknown substance during a house raid.
The officers, from the West Midlands Police force, were carrying out a search at a house in the Bordesley Green area of Birmingham at around 00.00 (31 August).
Three men, aged 21, 27 and 34, were arrested on suspicion of conspiracy to possess a controlled drug with intent to supply.
Police say they also seized a "very large" quantity of suspected Class A drugs with an approximate street value of around £250,000.
During the raid, officers were exposed to an unknown substance, which caused ill-effects for both the officers and the people arrested, namely sickness and breathing difficulties.
Eight police officers and the three people arrested were taken to Heartlands Hospital.
All were discharged this morning.
“Police officers face threats on a daily basis and, on occasions, criminals will use extreme measures to resist arrest.
“What happened overnight demonstrates the ongoing commitment and bravery of officers as they work to keep our streets safe.
“Events such as this always raise concern in communities, but I want to be clear that this is about drugs alone and not connected to terrorism.
– Chief Inspector Lee Wharmby, Force Incident Manager
“A long term operation, ‘No Deal’, is already underway targeting drug dealing across Birmingham, during which efforts have been focussed on two organised crime groups responsible for the supply of cocaine and heroin in the local area.
“Following a long-term covert operation and a series of co-ordinated raids during March 2012, a total of 39 individuals were arrested for various drugs offences, with 26 already sentenced for supplying drugs.”