Vomitings and diarrhoea can delay menses

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Can Vomiting and Diarrhea Delay Menses?

The short answer: Yes, but only indirectly. Vomiting and diarrhea do not act directly on the uterus or ovaries. Instead, they trigger a chain of stress-related hormonal events that can delay or suppress ovulation, which in turn delays or prevents menstruation.

The Mechanism: Stress Disrupts the HPO Axis

The menstrual cycle is regulated through a tightly coordinated interaction between the hypothalamus, pituitary gland, and ovaries (HPO axis). The hypothalamus releases GnRH in pulses, which drives pituitary secretion of LH and FSH, which in turn drive ovulation and the hormonal changes that produce menstruation.

This system is very sensitive to physical and psychological stressors. As stated in Kaplan & Sadock's Comprehensive Textbook of Psychiatry:

"There appears to be a dose-response relationship between the type, severity, and number of stresses on one hand and the proportion of women who develop anovulation on the other."

When vomiting and diarrhea occur (especially severely), they create the following stressors:

Stressor	Effect on Reproductive Axis
Physical illness/systemic stress	Activates the HPA axis; raises cortisol
Elevated cortisol	Directly slows GnRH pulsatility amplitude and frequency
Caloric deficit / dehydration	Energy deprivation further suppresses GnRH
Endorphin release	Also inhibits GnRH pulsatile release
Reduced GnRH pulses	Pituitary produces less LH and FSH
Low LH/FSH	Follicle fails to mature; ovulation is delayed or absent
No ovulation	No corpus luteum; no progesterone surge; endometrium is not primed to shed on schedule

The result is delayed ovulation --> delayed menstruation, or in severe/prolonged cases, amenorrhea (complete absence of menses).

Important Distinctions

Temporary vs. prolonged: A single acute episode of gastroenteritis causing brief vomiting/diarrhea is unlikely to cause significant menstrual delay. It is the severity, duration, and combination with other stressors (weight loss, poor nutrition, psychological stress) that matters.
The cause is ovulation delay, not uterine changes: Menstruation is the consequence of a failed pregnancy after ovulation. If ovulation is delayed by 1-2 weeks due to stress, menstruation will come correspondingly later. The uterus itself is not affected by gastroenteritis.
Malabsorption matters: Severe diarrhea can impair absorption of key nutrients (zinc, B vitamins, magnesium) and cause significant caloric deficit. This nutritional disruption is a recognized contributor to hypothalamic suppression of the reproductive axis. - Kaplan & Sadock's Comprehensive Textbook of Psychiatry, p. 7813
Not a reliable contraceptive: Some people mistakenly think vomiting/diarrhea after taking oral contraceptive pills can only affect the pill's efficacy (which is true - OCP may not be absorbed). But in the context of a natural cycle, vomiting/diarrhea delays menses only through the stress mechanism above, not reliably.

Summary

Vomiting and diarrhea can delay menses via:

Activation of the HPA axis (elevated cortisol)
Suppression of GnRH pulsatility
Resulting hypogonadotropic anovulation (delayed or absent LH/FSH surge)
Delayed or absent ovulation --> delayed menstruation

This is the same biological mechanism seen in athletes with energy deficiency, women with eating disorders, or anyone under significant physical or psychological stress. The more severe the illness (e.g., prolonged gastroenteritis with marked weight loss and dehydration), the more likely it is to cause a noticeable menstrual delay.

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