血清素选择性再摄取抑制剂
and
选择性血清素再摄取抑制剂
mean the same thing, but
血清素选择性再摄取抑制剂 keeps the word order the same as the original text.
In the text, "serotine/serotonin" and "selective" act as adjectives to "reuptake inhibitors". The order of the adjectives does not change the meaning of the text.

But in some situations, it would be awkward to change the order of the adjectives:
e.g. A big black bear, not a black big bear. (一只大黑熊，而不是一只黑大熊)。