Three people have died this week following suspected drug overdoses.
Police are not linking the incidents, which happened in Worthing and Billingshurst, but are appealing for information.
A 28-year-old man was discovered in the bathroom of a flat in Rowlands Road, Worthing, on Wednesday night.
It is believed he had taken heroin.
A post mortem examination of the body will be held and the coroner has been informed.
At about 8.20pm yesterday evening, police attended a flat in Durrington Gardens, The Causeway, Goring.
There they found a 60-year-old man being treated by paramedics for a suspected heroin overdose.
He did not respond and was pronounced dead at 8.40pm.
A 27-year-old woman who was present in the flat was arrested on suspicion of being concerned in the supply of a Class A drug is currently in custody awaiting interview.
At half-past midnight this morning police were called to a flat in Bridgewater Close, Billingshurst.
There they found a 33-year-old woman being treated by paramedics for a suspected heroin overdose.
She did not respond and was pronounced dead at 1.30am.
A 21-year-old man who was present in the flat, and who had also used heroin, was arrested on suspicion of being concerned in the supply of a Class A drug.
He was treated at the East Surrey Hospital, Redhill, before being taken into custody pending interview.
Detective Inspector Dave Wardley Wilkins, of the Sussex Police priority crime team, said: "This is one of three deaths in West Sussex in as many days, all of which are believed to have involved drugs.
"There is no reason to link them at this stage, but it is clearly something we are mindful of as we await the results of post mortem examinations and forensic tests in each case.
“Drugs can have a devastating effect on the lives of individual drug users, their families and the wider community.
“Any drugs-related death means a personal and tragic loss of life for that person's loved ones and this should never be forgotten."
Anyone who has any information on the supply or selling of illegal drugs is asked to call 101 or email firstname.lastname@example.org.