The prevalence of anticipatory nausea and vomiting (emesis) (ANV) has varied, owing to changing definitions and assessment methods. However, anticipatory nausea appears to occur in approximately 29% of patients receiving chemotherapy (about one of three patients), while anticipatory vomiting appears to occur in 11% of patients (about one of ten patients). With the introduction of new pharmacologic agents (5-HT3 receptor antagonists), it was anticipated that the prevalence of ANV might decline; however, studies have shown mixed results. One study found a lower incidence of ANV, and three studies found comparable incidence rates.[2,4,5] It appears that the 5-HT3 agents reduce postchemotherapy vomiting but not postchemotherapy nausea,[2,5] and the resulting impact on ANV is unclear.
Nausea and vomiting are the only reported adverse effects associated with the use of Essiac. Reviewed in  The manufacturer of Flor Essence states that users may experience increased bowel movements, frequent urination, swollen glands, skin blemishes, flu-like symptoms, or slight headaches.
Herbal treatments. In: US Congress, Office of Technology Assessment.: Unconventional Cancer Treatments. Washington, DC: U.S. Government Printing Office, 1990. OTA-H-405,...
Although other theoretical mechanisms have been proposed, ANV appears to be best explained by classical conditioning (also known as Pavlovian or respondent conditioning). In classical conditioning, a previously neutral stimulus (e.g., smells of the chemotherapy environment) elicits a conditioned response (e.g., ANV) after a number of prior pairings or learning trials. In cancer chemotherapy, the first few chemotherapy infusions are the learning trials. The chemotherapy drugs are the unconditioned stimuli that elicit postchemotherapy nausea and vomiting (N&V) (in some patients). The drugs are paired with a variety of other neutral, environmental stimuli (e.g., smells of the setting, oncology nurse, chemotherapy room). These previously neutral stimuli then become conditioned stimuli and elicit ANV in future chemotherapy cycles. ANV is not an indication of psychopathology but is rather a learned response that, in other life situations (e.g., food poisoning), results in adaptive avoidance. A variety of correlational studies provide empirical support for classical conditioning. For example, the prevalence of ANV prior to any chemotherapy is very rare, and few patients ever experience ANV without prior postchemotherapy nausea. Also, most studies have found (1) a higher probability of ANV with increasing numbers of chemotherapy infusions and (2) the intensity of ANV increasing as patients get closer to the actual time of their infusion. In one experimental study, it was shown that a novel beverage could become a conditioned stimulus to nausea when paired with several chemotherapy treatments.
Variables Correlated with ANV
Many variables have been investigated as potential factors that correlate with the incidence of ANV in hopes of developing a list of risk factors. There is currently no agreement on which factors predict ANV. A patient with fewer than three of the first eight characteristics listed below, however, is unlikely to develop ANV, and screening following the first chemotherapy infusion could identify those patients at increased risk.
Variables Found to Correlate With ANV
Age younger than 50 years.
N&V after last chemotherapy session.
Posttreatment nausea described as moderate, severe, or intolerable.
Posttreatment vomiting described as moderate, severe, or intolerable.
Feeling warm or hot all over after last chemotherapy session.
Susceptibility to motion sickness.
Sweating after last chemotherapy session.
Generalized weakness after last chemotherapy session.
High-state anxiety (anxiety reactive to specific situations).[12,13]
Greater reactivity of the autonomic nervous system and slower reaction time.
Patient expectations of chemotherapy-related nausea before beginning treatment.[15,16]
Percentage of infusions of chemotherapy followed by nausea.