Detectives launched an inquiry into steroid-dealing after a 23-year-old’s death.
Police believe Lewis Allan, who died early on Monday morning after falling ill at home in Eastbourne, used anabolic steroids over the last year.
They have arrested a man on suspicion of supplying drugs.
Mr Allan was taken ill at his home in Bridgemere Road, Eastbourne, at about 2am on Monday.
He was taken to Eastbourne District General Hospital but was pronounced dead shortly after 3.30am.
Sussex Police are investigating his use of anabolic steroids – a prescription drug sometimes used by bodybuilders.
Possession or importation of the drug for personal use is legal, but supplying it is illegal.
Officers believe Mr Allan’s weight had grown by as much as four stones over the last year as he trained.
His death is being treated as unexplained but not suspicious. The East Sussex Coroner is expected to hold an inquest and a post-mortem examination has not yet taken place.