Answer:
The sentence ' The health benefits of tea have been the subject of much research; in addition to its possibilities for preventing and inhibiting some forms of cancer, the brewed leaves of Camellia sinensis may also play a role in reducing the risk of heart disease and stroke' can be properly written in the following format.
The health benefits of tea have been the subject of much research; besides possibly preventing or inhibiting some forms of cancer, the brewed leaves of Camellia sinensis may also play a role in reducing the risk of heart disease and stroke.
This is because with a plural subject, a singular pronoun cannot be used. Hence, it or it's cannot be used.