As with any drug, dose-dependent toxicity is always a concern. As a spice it is, it is not meant to be taken in huge amounts. Otherwise, its consumption should not be a problem at all unless there's a known allergy to the spice, in which case a specialized medical evaluation is indicated to rule out any other cross-allergy.
Without getting in deep with molecular mechanisms, which I guess are not really known, most of its effects and cultural uses (asthma treatment, depression treatment, Alzheimer's treatment) must related to some sort of anti-inflammatory action. Interesting indeed.