tachyphylactic

noun

1. Medicine/Medical. immediate, temporary immunization against the effects of injection of a toxic extract owing to previous small injections of the same extract.
2. a decreased response to a medicine given over a period of time so that larger doses are required to produce the same response.

noun

1. very rapid development of tolerance or immunity to the effects of a drug

n.

1. Rapid desensitization to a pharmacologically or physiologically active substance, produced by inoculation with a series of small doses.
2. A rapidly decreasing response to a drug following its initial administration.