Why does heroin make a new user vomit?
Because opioid-related nausea is so common, it will be discussed separately. Opioids result in nausea through two major mechanisms: inhibition of gut motility and stimulation of the CTZ. Stimulation of the CTZ relates more to increases in blood opioid levels than it does to absolute opioid levels. Thus, initiating opioid therapy or raising the opioid dose is likely to result in nausea. However, if a new steady-state blood level is maintained, nausea usually subsides within two to three days. During this time aggressive treatment of nausea usually allows patients to tolerate opioid therapy. This is particularly important if the oral route is used for administration. Patients may enter a vicious cycle of nausea interrupting oral opioid administration, resulting in fluctuating blood opioid levels and perpetual nausea (in addition to unnecessary pain). In severe cases a nonoral route of administration should be used, at least until nausea is under control, in order to escape this cycle. As
