Rhesus Menstrual Cycles Recovered During Continued THC Exposure in a Historical Experiment

A 1983 rhesus-monkey experiment reported menstrual disruption followed by recovery of cycles and hormone concentrations during prolonged THC administration. Recovery during continued exposure suggested tolerance to the measured reproductive effects.

The exposure was repeated injection

Sexually mature female rhesus monkeys received THC injections three times weekly over a prolonged period. Menstrual cycles were disrupted for several months, with absent ovulation and lower basal plasma gonadotropin and sex-steroid concentrations. These were controlled primate observations, not clinical records of human cannabis users.

Later recovery was part of the result

Normal cycles and hormone concentrations subsequently returned. Omitting that later phase would misstate the experiment, just as omitting the initial disruption would. A normal later measurement also cannot retrospectively establish that earlier function was unchanged.

Tolerance was tied to particular reproductive measures

The authors interpreted the recovery as tolerance to menstrual-cycle disruption. The abstract does not establish that fertility, pregnancy outcomes or every endocrine response was normal. Nor does tolerance on these measures demonstrate tolerance to cognitive or cardiovascular THC effects.

The study illustrates how an exposure effect can change over months rather than remaining static. Its historical injected regimen does not provide a human fertility prognosis or a safe-use rule. The appropriate conclusion keeps initial disruption, later recovery, plasma hormone measurements and species boundaries together.

Related: interpreting cannabis tolerance claims.

Research cited

Smith CG; Almirez RG; Berenberg J; Asch RH. Tolerance develops to the disruptive effects of delta 9-tetrahydrocannabinol on primate menstrual cycle. Science (New York, N.Y.) (1983). doi:10.1126/science.6298938. Findings discussed from the study abstract.