1560s, "sudden and apparently causeless turn of mind," of unknown origin. Perhaps it is from a dialectal survival of a word related to Middle English friken "to move nimbly or briskly," from Old English frician "to dance" [OED, Barnhart]. There is a freking attested in mid-15c., apparently meaning "capricious behavior, whims." Or perhaps from Middle English frek "eager, zealous, bold, brave, fierce" (see freak (n.2)).
The sense of "capricious notion" (1560s) and that of "unusual thing, fancy" (1784) preceded that of "abnormally developed individual or production" (first attested in freak of nature, 1839, which later was popular in variety show advertisements for bearded ladies, albinos, etc.; compare Latin lusus naturæ, which was used in English from 1660s). As "drug user" (usually appended to the name of the drug) it attested by 1945. The sense in health freak, ecology freak, etc. is attested from 1908 (originally Kodak freak "a camera buff"). Freak show is attested from 1887.
also freakout "bad psychedelic drug trip," or something comparable to one, 1966, from verbal phrase freak out, attested from 1965 in the drug sense (from 1902 in a sense "change, distort, come out of alignment"); see freak (n.). There is a coincidental appearance of the phrase in "Fanny Hill:"
She had had her freak out, and had pretty plentifully drowned her curiosity in a glut of pleasure .... [Cleland, "Memoirs of a Woman of Pleasure," 1749]
where the sense is "she had concluded her prank."
1580s, "act of keeping under authority and regulation, fact of checking and directing action," from control (v.). Meaning "a check, restraint" is from 1590s. Meaning "a standard of comparison in scientific experiments" is by 1857, probably from German Controleversuche. Airport control tower is from 1920; control-room is from 1897. Control freak "person who feels an obsessive need to have command of any situation" is by 1969.
1972 (also as a verb), originally in phone phreak, one of a set of technically creative people who electronically hacked or defrauded telephone companies of the day.
The phreaks first appeared on the US scene in the early 1960s, when a group of MIT students were found to have conducted a late night dialling experiment on the Defense Department's secret network. They were rewarded with jobs when they explained their system to Bell investigators. ... The name "phone phreak" identified the enthisiasts with the common underground usage of freak as someone who was cool and used drugs. [New Scientist, Dec. 13, 1973]
The ph- in phone may have suggested the alteration, and this seems to be the original of the 1990s slang fad for substituting ph- for f- (as in phat).