Nausea is not an allergic reaction, but rather a normal function of the brain. It is a highly distressing queasy feeling that alerts your brain to the possibility of throwing up. Nausea may occur with or without vomiting, but it typically, though not definitively, occurs before vomiting.
Opioid induced nausea
Nausea is one of the most prevalent adverse effects of heroin use. In fact, within hospitals, nausea is expected to occur in 25 – 30 percent of patients treated with opioid drugs. However, since heroin involves greater average dosing and subsequent amplified effects it results in higher than average nauseating events. Scientific studies also indicate opioid induced nausea and vomiting events are less likely to occur in men than in women and are less likely in whites than in blacks.
Heroin causes nausea
The first time a person uses heroin he or she is likely to get nauseous and throw up. This is not a rule, but it is very common. Strangely enough, getting queasy, nauseous and occasionally vomiting are normal parts of the heroin addict lifestyle. In truth, many heroin addicts glean pleasure from throwing up. The reason being, because heroin addicts perceive it to mean “strong heroin.” Over the drug addict career, tolerance will develop to both nausea and vomiting, and eventually these uncomfortable side effects fade away. Unfortunately, they will be supplanted by other uncomfortable side effects, including itching, constipation and urine retention.
Chemoreceptor trigger zone
Immediately after heroin is administered, it metabolizes into 6-monoacetylmorphine (6-MAM) which subsequently triggers the release of dopamine. The more 6-MAM and/or dopamine are detected by the D2 receptors within the Chemoreceptor Trigger Zone (CTZ), the greater the potential for an emetic response. Although the precise mechanisms of heroin-induced nausea and vomiting are not entirely certain, it appears that stimulation of the CTZ, and opioid receptors in the GI tract are both involved.
The CTZ is part of the medulla oblongata, which is the lowest part of the brain stem, which is at the base of the brain connected to the spinal cord. The medulla oblongata is also the oldest part of the nervous system and is responsible for many involuntary functions, such as heart rate, breathing, sneezing and vomiting.