A group of 15 subjects who have used marihuana infrequently and a group of 15 subjects who have used the drug frequently were intravenously infused with Δ9-tetrahydrocannabinol.
In spite of the marked differences in marihuana use, the groups did not differ significantly in the amount of Δ9-THC necessary for its effects to be perceived, to accelerate the heart 25% above the base line levels, the total dose administered, the maximum level of "high," the maximum heart rate acceleration, and the heart rate acceleration observed 15 minutes after the beginning of the infusion.
This is evidence that marihuana, as currently used by young Americans does not produce tolerance or sensitivity to its effects.
Perez-Reyes M, Timmons MC, Wall ME. Long-Term Use of Marihuana and the Development of Tolerance or Sensitivity toΔ9Tetrahydrocannabinol. Arch Gen Psychiatry. 1974;31(1):89-91. doi:10.1001/archpsyc.1974.01760130067011