Nimodipine controlled the escalation of the morphine dose in 9 patients (65%), and placebo in 4 (28%), the difference being statistically significant (P=0.03).
Consistent with rat data. This is from 1998. I'm sure there's more evidence by now. It's been a while since i researched this, but I think I've previously seen at least one other study.
These results suggest that the elevation of the cyclic AMP levels is involved in the development of morphine withdrawal syndrome and that blockade of the morphine-induced reduction of cyclic AMP levels by chronic rolipram inhibits the development of dependence and the behavioural and biochemical changes induced by naloxone. Furthermore, rolipram may be a useful drug for attenuating the development of morphine dependence.
Excellent. This implies that theobromine may help prevent opioid tolerance.