“A suspension of (−)-Δ9-trans-tetrahydrocannabinol (Δ9-THC) was administered daily for one week by i.p. injection to female rats showing the syndrome of adrenal regeneration hypertension (ARH)…

The findings indicate that Δ9-THC, at a moderate dose for the rat, is capable of lowering the blood pressure in rats suffering from adrenal regeneration hypertension and that chronic administration of Δ9-THC does not appear to stimulate the pituitary-adrenal axis, in contrast to reported effects of acute administration.”

 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1776093/

http://www.thctotalhealthcare.com/category/hypertension-high-blood-pressure/