The victims, two men and two women, received the health cocktail at the same doctor at a private homeopathic clinic.
The deceased have been identified as Jesús Héctor Almeida Flores and his son Sebastián Almeida Cáñez, as well as Catalina Figueroa and Dinora Ontiveros.
They allegedly received the injection at the Cellular Regenerative Biological Medicine in Hermosillo, Mexico, prompting an investigation by state authorities into possible medical malpractice.
The clinic has been described in local reports as offering homeopathic and regenerative treatments.
Symptoms appeared rapidly after the injections, leading to severe deterioration, hospitalisation and death.
One victim, Dinora Ontiveros, received the serum on 24 February and died on 2 March.
Her uncle presented similar symptoms after receiving the same treatment on the same day.
He was hospitalised in a private clinic where he managed to survive.
Jesús and Sebastián were treated by the same doctor in late March and passed away days later.
Catalina Figueroa had the jab on 1 April and died within 24 hours, as reported by Need To Know.
Her brother, Diego Figueroa, said: “They gave her the serum and she started feeling very bad.”
The state public prosecutor’s office has confirmed they are investigating the four linked deaths.
Investigators searched the clinic and seized clinical records, bottled medical solutions, injectable medications, computer equipment, and video recording devices on Wednesday (1 Apr).
The premises were sealed by the health authorities.
Samples of the seized substances were sent to a lab to check for contamination or harmful components.
Meanwhile, tissue samples from the victims are undergoing analysis to determine the exact cellular damage and cause of death.
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