Green’s Dictionary of Slang

come on v.2

[SE come on, to begin]

1. (drugs) for withdrawal symptoms to start affecting a narcotics addict.

[US]D. Maurer ‘Lang. of the Und. Narcotic Addict’ Pt 2 in Lang. Und. (1981) 102/1: To feel the habit coming on. See to be sick.

2. (drugs) for a drug to begin affecting its user, esp. of a hallucinogen (which takes a short time to enter the bloodstream and hit the brain).

[US]Mezzrow & Wolfe Really the Blues 92: Muta never came on like that.
[US]E. Bunker No Beast So Fierce 214: The marijuana came on quickly.
[US](con. 1969–70) D. Bodey F.N.G. (1988) 103: Whatever that pill is, it’s coming on hard now.

3. of a woman, to start menstruating.

[UK]P. Bailey Eng. Madam 45: I’d clicked with him once before, and he gave me some pills [...] and I came on again after taking them.
[UK]K. Sampson Powder 130: All the girls had come on their period that night.
OnLine Dict. of Playground Sl. [Internet] come on v. to begin menstruation.