For two years until he was caught last year, a pharmacist sold about 20,400 bottles of cough syrup containing codeine, which can be abused as a drug, to customers at his Bukit Timah Plaza dispensary.
The total volume was nearly 2,500 litres, which saw William Woo Tat Meng make a profit of more than $240,000.
It was an illegal trade he had been carrying out for a decade.
Yesterday, the 58-year-old sole proprietor of Community Pharmacy was jailed for eight months and three weeks, becoming the first pharmacist to be found guilty of improperly selling codeine under the Poisons Act.
Under the law, pharmacists are not allowed to sell more than 240ml of codeine cough syrup to a customer at any one time. They also have to record the name and identity card number of the customer, and the quantity of codeine cough syrup sold daily in a book kept solely for this purpose.
Instead, Woo, who also pleaded guilty to giving false information to a Health Sciences Authority (HSA) officer, falsified his company records to cover his tracks.
Codeine is a narcotic drug often used in cough syrup. However, people can become addicted to the calming or euphoric feelings that it produces. Prolonged use leads to organ damage.
HSA started probing Community Pharmacy in March last year after realising that the dispensary had ordered large quantities of Dhasedyl syrup, containing codeine, between May 7, 2013, and April 23 last year.
On April 10 last year, when HSA carried out an audit at the pharmacy, Woo produced a dispensing ledger dated "Feb 2015 to April 2015", which he had doctored.
At about 3pm on April 23 last year, HSA officers stopped a 42-year-old man who had just left the dispensary.
The man had 14 bottles, each containing 120ml of Dhasedyl syrup. He had paid $20 for each bottle and Woo had not asked for his particulars. The man said he had been buying cough syrup from Community Pharmacy since 2000, after finding out that he could buy it easily there.
At about 5.30pm that same day, HSA officers asked Woo for records of Community Pharmacy's latest sales of codeine cough mixture. He gave them a book titled "April 2015" but, while the officers were looking through it, Woo admitted that he had entered 14 fictitious names for the sale of 14 bottles earlier.
Woo said he had updated his dispensing ledger by making fictitious entries of a person's particulars or by re-entering past customers' details. He also admitted to selling Dhasedyl syrup for about 10 years.
• Additional reporting by Linette Lai