He is the hospital pharmacist of the Netherlands Cancer Institute/Antoni van Leeuwenhoekziekenhuis and previously held the same position at the Slotervaartziekenhuis.
The board members including Beijnen wished to sell the hospital to a certain party while the previous director sought to prevent this.
[4][5] After resigning from the board Beijnen stayed on as the hospital pharmacist of the combined Netherlands Cancer Institute/Antoni van Leeuwenhoekziekenhuis.
[4] As hospital pharmacist of the Slotervaartziekenhuis Beijnen was since 1998 involved in the scientific experiment of selling heroin in a controlled environment to local addicts.
[6] A monopoly position was granted by the Ministry of Health, Welfare and Sport to the Slotervaartziekenhuis for the production of heroin.