"Insane in the Brain" earned a 3× platinum certification from the Recording Industry Association of America and sold 3,000,000 copies domestically.

[6] According to a live interview aired on Double J during a feature of the Black Sunday album,[7] "insane in the membrane" was a localised gang term used at the time by the Crips when doing something crazy.

'However, less than two months later in an interview with British newspaper The Guardian, Muggs then claimed the sound effect was made by a horn and not a guitar.

[11] This has since caused disbelief that Muggs is telling the truth and that the sample may well be the horse from Mel and Tim's "Good Guys Only Win in the Movies", as Muggs has claimed himself that he has "a foggy memory when it comes to the samples used on 'Insane in the Brain'"[8] due to the fact that at the time of the song's production, "there was a lot of weed smoked"[6] and that he confirmed he was "not musically trained, never went to music school and I don't play instruments".

Resting on a beat-bed of loopy samples and nimble scratches, act drops rhymes that are even sharper than on previous efforts.

[16] A reviewer from Music & Media commented, "If you think you're going slightly mad, you haven't heard this Hispanic gangsta rap outfit yet.

"[17] Andy Beevers from Music Week gave it three out of five, calling it an "excellent new single from LA's celebrated smokers" and "a tough funky track."

"[18] Keith Cameron from NME named it Single of This Week, stating that "Insane in the Brain" "is definitive CH, with whistling kettle feedback blasts all over the (cough) joint, dopey drum kicks causing you to prance foolishly round the kitchen and B-Real throwing down a gauntlet of sorts..."[19] NME editor Johnny Cigarettes declared it as "a stomping pant-swinger of a party record".

[22] Another RM editor, Richard Russell, wrote, "While this covers pretty much the same ground as the debut LP, it will help to satiate the appetite of countless Cypress fans hungry for new material.

[25] Charles Aaron from Spin felt that "DJ Muggs's sample-squeal perfectly mirrors the reckless, loony edge in B-Real's voice, and it goes straight to your head (and so on).

But what's remarkable is not that such a pro-drug, anti-cop stance is in heavy pop rotation, but that the song's repetitive drum-whack makes you wonder: "Goin' insane..."?