But they are now stockpiling foreign-made everyday medications, such as paracetamol and cough syrup and lugging them back home.

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Jiang Xiao, from Fuzhou in Fujian province, spent a week travelling in Okinawa last month. Aside from the usual tourist purchases, she bought eye drops, nasal sprays, pain-control medication and the country’s signature liquid adhesive plaster.

“In shops there I saw many Chinese were buying many more drugs than me,” Jiang said. “I don’t buy children’s drugs in Japan because I have already bought a lot through a US online drug selling platform.”

She said mainlanders didn’t trust the domestic equivalents. “Mainland pharmaceutical products have many problems. For example, I heard that some drugs contain excessive antibiotics,” she said.

Mainland authorities have had some success in tackling counterfeits in drug manufacturing, closing down home factories that often operate amid poor hygienic conditions. But as more consumers travel abroad with greater frequency, they would rather add some stops at pharmacies to their itineraries than take a chance on a domestic brand.

The flood of interest by Chinese consumers prompted Japan’s Home Medicine Association to launch a Chinese-language website last year, providing information on 80 products from 26 membership companies. The association consists 90 per cent of the nation’s over-the-counter drug manufacturers that control 30 per cent of the market.

“The OTC drug market in Japan has long been on a downward trend, but the surge in purchasing by foreign customers has boosted sales by about 110 per cent in 2015 over the previous year,” Fujii Ryuta, the association’s vice-president, told South China Morning Post.

China has become the largest source of foreign visitors to Japan, with the number doubling to five million last year, according to the Japan National Tourism Organisation, the Oriental Morning Post reports.

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Their total consumption increased by 2.5 times, year on year, to 1.4 trillion yen, accounting for 40 per cent of all foreign tourists spending.

Pharmacies across Japan are posting advertisement not only in Japanese but also in Chinese, while some stores are hiring more Putonghua-speaking staff to better cope with the demand.

Fujii said the consumers appreciated products that were strictly regulated with the needs of the end user carefully considered.

“The packaging of Japanese commodities are genuinely colourful, beautiful and moreover very functional, and the information ... is put on the outside, which gives customers a sense of confidence,” he said. “As for OTC drugs, it’s the same as well.”

The mainland public is divided in its views of the trend of buying overseas, with some people calling it a national “betrayal”.

Last month Wang Xuehai, a political adviser in the central province of Hubei who is also the chairman of Humanwell Healthcare Group, said it was a shame for Chinese companies to see people go to Japan to buy simple cold medication, Cnhubei.com reports.

Individual traders on the mainland are trying cash in on the demand by buying overseas medication for resale at home, but they run afoul of the law without the proper permits.

In 2014 a man operating an online shop based in Ningbo in the eastern province of Zhejiang was sentenced to two months in jail, with six months suspended, for selling children’s cough and cold medication bought from the United States, the Ningbo Evening News reported.

It’s illegal to sell drugs on the mainland without a certificate, said Li Hu, an analyst from industry research firm Zero Power Intelligence Group.

“If the agent sells the drugs [bought from abroad], they will be charged,” he told the Post.