Rasayan tantra(रसायन तंत्र):
Rasayan a word contains two subwords ras+ayan, ras refers to ras rakta and dhatu of body. And ayan means “way of acquiring”. Combine definition can be “a study of rejuvenation of the body, prevention of diseases, aging symptoms, and a way of long and healthy life. Rasayan medicines are used to prevent diseases, detoxification, and immunology.
Vajikaran tantra(वाजीकरण तंत्र):
A branch of Ayurveda in which reproduction capacity, impotency, sperms related diseases, sperm deficiency, physical weakness, etc. are treated is called as Vajikaran. it looks after improving physical strength, increasing sexual potency, pleasure, and behavior through herbal and ayurvedic medicines. in other words a “science of aphrodisiacs”.
Reference
Ajay Jadhav