First, tonic becomes poison, but let's talk about the answer in the book. Since Shen Nantang was attracted by Wu Zetian, he has lived a life of singing every night. But as the old saying goes, there are no plowed fields, only exhausted cows, so his body is overdrawn very seriously, so he began to use a lot of tonics. We all know that drugs are toxic in three points, not to mention eating so much, and tonics have become poison, and he is also a physician himself, not a military commander, so he can only show it to Wu Zetian in vain.
Second, there is no specific record that Shen Nan is Toy Boy of Wu Zetian. In Old Tang Shu, there is only one mention, and there is basically no specific story about him, so it is possible that he and Wu Zetian had only one night's story at that time, or just one obscure one among many Toy Boy, but what about in Old Tang Shu? Xue Huaiyi Biography once mentioned Shen Nanzhang.
Third, the history of a fire Xue Huaiyi was Wu Zetian's first Toy Boy, and the first one was definitely fresh, so Xue Huaiyi was well treated and deeply loved by Wu Zetian. But later, Wu Zetian went to Shen Nan, where Xue Huaiyi was not favored by competition. As a result, Xue Huaiyi burned Tang Ming in a rage, and it was this fire that more or less recorded some records of the physician Shen Nan.