If you refer to what is called sea costus (the literal translation of Al-Qust Al-Bahri which is a white kind of costus which used to be brought from India to the Arab Peninsula in ships across the sea and that is why it was called sea costus), then it was mentioned in many Ahaadeeth (narrations). Among the places where it is mentioned is the Hadeeth narrated by Anas who said, “The Prophet said: “The best medicines you may treat yourselves with are cupping and sea costus.” [Al-Bukhari and Muslim]
When interpreting the above Hadeeth, and clarifying the benefits of sea costus, An-Nawawi said, “Physicians unanimously agreed in their books that sea costus increases urine and menstrual flow, is beneficial against poison, enhances sexual desire, kills worms…etc." As regards whether it needs to be mixed with black seeds for the purpose that you mentioned in the question, then this matter could only be determined by people who are experienced in treating with herbs.
There is another kind of costus that is called the Indian costus which differs in some of characteristics from the sea costus. Ibn Al-Qayyim said in Zaad Al-Ma’aad, “There are two kinds of costus: the white kind that is called sea costus and the Indian costus which has the hottest nature among them, while the white type is the mildest. Both kinds have numerous benefits.”
Moreover, Al-Munaawi said, “The sea costus is called the Makkan one and it is distinguished by its white color from the Indian costus which is black and the first kind is the best among the two.”
Allaah Knows best.