Hyssop smells sweet and camphorous, somewhere between rosemary and a cough sweet. Up to half the oil is pinocamphone and its close relative, ketones that loosen mucus and help clear a blocked nose.^[1] The same ketones are toxic to the nervous system in quantity.^[3] Avoid it in epilepsy and pregnancy, and keep it well diluted.^[3] On isolated gut muscle the oil relaxed contractions, which fits its old use for cramps and coughs.^[2]