JINAN -- Zhou Han tasted donkey-hide gelatin, known as ejiao in Chinese, for the first time to relieve her period pain.

Zhou's mother purchased 250 grams of ejiao at a cost of 700 yuan ($105) in a drug store after she heard that the traditional Chinese healthcare product can enrich blood and benefit women's skin.

The store processed the medicine into a paste mixing it with ingredients such as walnuts, red dates and rice wine. The 25-year-old Zhou takes it twice daily.

"I felt comfortable in the first weeks after I tried it," said Zhou, who works at a PR company.

With a history of around 2,500 years, ejiao is made by soaking and stewing donkey skin and refining the results into a tonic. There are claims that it can tonify blood, boost immunity and treat a range of ailments from anemia and dry coughs to dizziness and insomnia.

Nowadays, it has been rebranded as a healthcare product used in food, drink or even face creams for the country's growing middle class.

According to the Qianzhan Industry Research Institute, the production of China's ejiao manufacturers has grown from 3,200 tonnes in 2013 to 5,600 tonnes in 2016, with an annual growth of more than 20 percent.

"More than 10 years ago, the consumers of donkey-hide gelatin were mainly from Yangtze River Delta. The medicine has become widely known by more Chinese now," said Cai Jun, a professor of nutritional studies at Longhua Hospital under Shanghai University of Traditional Chinese Medicine (TCM),

Donkey-hide gelatin has seen its price soar.

In late November, Dong'e Ejiao Co. Ltd, China's largest donkey-hide gelatin producer, announced it had raised the ex-factory price of its two major products, ejiao in solid bars and mixed with other ingredients in syrup form, by 10 percent and five percent, respectively.

According to Wang Min, an analyst with a Shandong-based consulting firm, the current ex-factory price of Dong'e Ejiao's bar is more than 12 times that of 2007, while its market price is 2,698 yuan ($408) per 500 grams, around 10 times that of 2007.

Other ejiao brands have also raised their prices on major e-commerce platforms, making what was once a common supplement for some Chinese, now a luxury item.

"The price of donkey-hide gelatin has rocketed up very fast. My monthly salary now equals less than 1.5 kilograms," said Ma Lei, a longtime consumer of donkey-hide gelatin from Jinan, capital of Shandong Province. Ma takes around one teaspoon of ejiao daily.

China's donkey population has nearly halved from 9.4 million in 1996 to 5.4 million in 2015, according to the National Bureau of Statistics.

Industry insiders believe that there are currently around 5 million donkeys in China, and the annual slaughter rate is about 1 million. Many donkey-hide gelatin manufacturers started importing the skin.

The scarcity of donkey skin has also led to the flooding of counterfeit products claiming to be donkey-hide gelatin onto the market. They may be made from the skins of mules, horses or pigs.

"Donkeys used to be a pack animal for farmers. However, as agricultural mechanization increases, fewer farmers are raising donkeys," said Zheng Zhong, who is in charge of Shandong Lyubang, a company which manages donkey-based food products.

"The animal's low fertility rate and long gestation period have also discouraged business people," said Zheng.

Critics argue that the efficacy of donkey-hide gelatin has been exaggerated.

"Consumers should be more rational," said Cai, advising that there are many cheaper food or herbs with similar functions for those who can not afford ejiao.

Despite the soaring price, Zhou Han's mother goes to drug stores regularly, purchasing donkey-hide gelatin for her daughter especially in winter.

"My mother said that I should keep eating it until a long-term effect can be seen. It provides a form of relief. Anyway it won't do any harm, right?" said Zhou.