Prosecutors are appealing for a stiffer sentence for a "defiant" doctor, who continued to sell codeine-laced cough syrup even while he was under investigation for doing so.
Tan Gek Young sold more than 2,300 litres of cough mixture at his Bedok clinic, one of the highest quantities of such illegal sales.
He paid an average of $39 for a gallon, which he sold for more than $1,000. The 61-year-old permanent resident made profits totalling more than $600,000 from the illicit sales between January 2014 and June 2015.
Deputy Public Prosecutor Tan Wen Hsien sought at least three years' jail and a $145,000 fine for Tan, to send a clear and strong deterrent message to medical professionals who may think of lining their pockets by selling cough mixture at huge mark-ups.
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She argued that all doctors and pharmacists convicted of illicit sales of cough mixture should be jailed and fined, and urged the court to lay down a sentencing framework.
While Tan was being investigated, he continued selling cough mixture and even scaled up his racket by selling it by the gallon instead of the usual 90ml bottles. The DPP said his original sentence of two years' jail and a $130,000 fine was manifestly inadequate.
She said the number of cases investigated by the authorities reached a high of 67 in 2015, compared with between 43 and 61 in the previous three years. The number for last year stood at 53 up till November.
Tan's lawyer, Mr Amogh Chakravarti, argued that the prosecutor's statistics were irrelevant because not all investigations eventually lead to a conviction.
He noted that of the 417 cases investigated by the Health Sciences Authority between 2009 and 2014, only 47 cases led to prosecution.
He argued than Tan's sentence was too harsh, pointing to the case of pharmacist Woo Tat Meng, who sold 2,452 litres but was jailed for eight months and three weeks.
A Straits Times check showed that drug abusers are still visiting clinics to get their fix but systems are in place to prevent abuse.
"One guy came in at 9pm, kicked up a lot of fuss and wasn't very friendly. He was defiant and aggressive, and he said he wanted cough medicine," said Dr Pak Mun Kwan of Milford Medical Group.
Dr Cheong Wai Chern of Raffles Medical Clementi said the clinic has records of how often a patient asks for cough medicine.
•Additional reporting by Winnie Tan
Correction note: This story has been edited to update the number of cases investigated by the authorities.