Claims a prisoner was mistreated at a custody suite by two Merseyside Police officers were based on hearsay, the police watchdog has said.
The man, who was arrested in Wallasey on Merseyside, spent six days in a HM Revenue and Customs (HMRC) facility after swallowing 26 wraps of cocaine.
Staff claimed two officers deliberately modified his cell's heat and lighting.
But the Independent Police Complaints Commission (IPCC) said there was no evidence to support the complaint.
The man was arrested on 27 May and taken to the HMRC suite at Manchester Airport, which specialises in monitoring prisoners suspected to have swallowed drugs.
The IPCC started an investigation after "serious concerns" were raised by HMRC staff about his treatment the following night, although the detainee refused to co-operate.
Investigators found no firm evidence that the temperature in his cell was modified regularly or by excessive amounts, the watchdog said.
During one three-hour period the man complained about being cold, but officers suggested this was a symptom of drug withdrawal symptoms.
However, the officers were advised about their future conduct after a review of the cctv
revealed that a conversation took place about not giving him a blanket and letting him "freeze".
Video evidence also revealed the detainee banging his forehead on the cell wall about 45 times in less than a minute - but officers did not visit him until 85 minutes later.
Naseem Malik, IPCC Commissioner for the North West, said: "Our investigators have found the witness accounts contradictory and some of the allegations appear to have stemmed from hearsay evidence.
"As a result there is no strong, independent evidence to support the main allegations of mistreatment and, therefore, these are not substantiated.
However some incidents have been captured on cctv
and these did identify some treatment which was inadequate.
As a result the Merseyside Police officers involved have been advised about their future conduct. THE BBC