Let’s talk about lean. Lil Wayne is apparently back on the sizzurp even though the cocktail’s codeine- and promethazine-fueled seizures landed him in the emergency room back in 2013. On their own, these substances are already incapacitating if taken in volume. Together, they slow you down with a one-two punch that induces a hypnotic and euphoric purple haze and can slow down bodily functions until breathing becomes laborious.

Most recipes for the cocktail, which became popular in the rap scene in 1980s Houston, call for three components: Sprite or Mountain Dew as a mixer, a Jolly Rancher as an optional flavor boost, and the main event, cough syrup — preferably purple — containing codeine and promethazine to dull reality’s edge through their combined euphoric and dissociative effects. The overall drowsy feeling finds its aural equivalent in A$AP Rocky’s “Purple Swag” or pretty much any song by Future, notably “Codeine Crazy” or “Dirty Sprite”.

Codeine belongs to a broad family of drugs known as opiates — its harder-hitting cousins are morphine and methadone — which are considered narcotics, or psychoactive compounds that induce sleep. It happens to be a really effective painkiller and cough suppressant, which makes it ideal for treating the headaches that come with a cold — and for inducing a body high. Sizzurp-induced euphoria is thought to be triggered when codeine molecules bind to mu opioid receptors in the brain, kicking off the reward pathway and increasing the transmission of dopamine, which can feel, to quote a wise hedonist, very naice.

Unfortunately, codeine is also very addictive, and at high enough doses, it can also slow breathing to the point of stopping because it acts on the part of the brain that controls respiration. That’s why it’s not recommended for people with respiratory issues, like asthma or the tendency to hyperventilate. (Bonus: It also has a constipating effect, which is why it’s sometimes used to treat diarrhea.)

The other big player in lean is promethazine, an antihistamine normally used to treat allergy symptoms like itching and runny noses. It’s thrown into the cough syrup mix for its sedative properties — it’s sometimes prescribed for insomnia — which are supposed to prevent people from having too much of it. At small doses, it’s perfectly safe, but because it acts as a sedative by slowing down the central nervous system — which, you know, controls all of the body’s activities — it’s kind of dangerous to mix it with a thing that already fucks with your breathing. The increased risk of seizures, unfortunately for Weezy, are just a really unfortunate side effect.

Lean’s effect on producers and audiences is largely considered to be the driving force behind chopped and screwed hip-hop, which originated with and arguably killed DJ Screw in Houston the mid-‘90s. In his book Every Song Ever, critic Ben Ratliff effectively sums up the genre — and with it, the combined effects of too much codeine and promethazine — calling it “devastating music, scarily adrift.”

Photos via World Star Hip Hop