The blood brain permeability of heroin is about 10 times that of morphine.[1,2] Once heroin crosses the blood brain barrier, it is hydrolyzed into 6-acetyl morphine and morphine, which then quickly bind to opioid receptors.[2,3] The “rush” felt by heroin users is the sensation caused by the rapid entry of heroin into the brain and the attachment of 6-acetyl morphine and morphine to opioid receptors. Opioids in general can change the neurochemical activity in the brain stem causing a depression in breathing. In the limbic system opioids cause an increase in feelings of pleasure, and have the ability to block pain signals sent through the spinal cord.
Click here to see an animation on how heroin works in the brain.
When heroin is injected or smoked, users typically feel two types of euphoric effects–a “rush” and a “high.” The rush usually lasts one to two minutes and occurs right after the drug is administered. It is described as an intense orgasmic feeling that is felt throughout the body, especially in the abdomen. Following the rush is a high that can last four to six hours. The feeling is described as warm and pleasant, with indifference to internal and external stimuli. The following characterizations may occur during a high:
Timing of Effects
Injecting heroin intravenously can produce a feeling of euphoria in seven to eight seconds. The peak effects of smoking heroin are similar to those obtained from intravenous injection. In contrast, injecting intramuscularly, also known as skin popping, leads to a slower onset of euphoria, taking five to eight minutes. The peak effects of snorting heroin occur in 10 to 15 minutes. Oral administration of heroin has little effect.