We know that heroin quickly metabolizes into morphine. Therefore, what morphine does in the body, heroin must do also. Scientific studies show that prolonged administration of morphine produces hyper-sensitivity to pain. This is a medical condition known as opioid induced hyperalgesia (OIH). Hyperalgesia is an increase in pain response to a stimulus. It’s not only morphine and heroin that causes hyperalgesia, but all opioid-based painkillers.



Hyperalgesia is a decrease in pain threshold after opioid exposure. In other words, things that normally cause pain at say, a 1 out of 10. Following opioid exposure, may now be a 6 out of 10. It is a paradoxical response because heroin, morphine and other opioid painkillers relieve pain, but now the person is experiencing more pain. Although the precise molecular mechanism is not completely understood, it is generally thought to result from neuroplastic changes in the peripheral and central nervous systems.



Neuroplasticity is the brain’s ability to reorganize itself by forming new neural connections throughout life. Neuroplasticity allows the neurons (nerve cells) in the brain to compensate for changes in their environment, such as drugs or injury, by adjusting their activities in response.


Scientific Studies


“The ability of repeated morphine administration to produce hyperalgesia was studied in rats. The hot plate procedure was used to measure changes in the animal’s response latency. The response latency was measured twice at 30-minute intervals, before the injection of the experimental agent and again at 30, 60, 90, 120, 180 and 240 minutes after drug administration. Morphine (5 mg/kg) or saline (2 ml/kg) was given s.c. for varying periods of time.

It was found that chronic morphine administration produced hyperalgesia between 60 and 120 minutes after the drug. This hyperalgesia was found not to be the result of a morphine-test interaction. Acute administration of nalorphine, 5 mg/kg, delayed the onset of the hyperahgesic response produced by morphine.” SABIH KAYAN, L. A. WOODS and C. L. MITCHELL


Hyperalgesia and heroin withdrawal

Hyperalgesia is a common problem for heroin addicts. The longer an addict uses heroin and the more heroin he or she uses the worse the problem gets. That’s why if a heroin addict tries to kick their habit they find themselves in pain. They are without their pain-reliever and they have become hypersensitive to pain. During heroin withdrawal, stimuli that was previously painless is now painful.


The good news is that the brain will effectively revert back to a more normal state after heroin detoxification and a short period of abstinence. The healthier the brain, which normally means the younger the brain, the more quickly this will occur.




how heroin works