As he grew older, he often came in conflict with his ambitious and powerful mother Empress Wu, and it is commonly believed by traditional historians that she poisoned him to death in 675.
After Emperor Taizong's death in 649, she, like all of his surviving concubines who did not bear children, was sent to Ganye Temple (感業寺) to be a Buddhist nun.
In 655, Consort Wu falsely accused Empress Wang and her mother Lady Liu of using witchcraft and of murdering her daughter.
Prior to this, in 652, Emperor Gaozong's oldest son (by his lowly-born concubine Consort Liu), Li Zhong, had been made the crown prince already, but Empress Wu had her ally, the official Xu Jingzong submit a petition arguing that now that the empress had her own sons, Li Zhong should step aside.
Li Hong was left in charge at Chang'an, although it was said that he was often ill, and the decisions were largely made by his staff members Dai Zhide, Zhang Wenguan, and Xiao Dezhao (蕭德昭).
Consort Xiao's daughters Princess Yiyang and Gao'an had, because of their mother, been put under house arrest inside the palace, so much so that they were not yet married even though they were over 39 years in age.
In anger, Empress Wu immediately married them to two palace guards named Quan Yi (權毅) and Wang Xu (王勗), and she became displeased at Li Hong.
At a later point, by order of Empress Wu Li Hong was no longer in command at Chang'an, and he went to Luoyang to join his parents.