Monoterpenes are organic compounds that are found in high concentrations on the flowers of the plant but may also be on the foliage and roots of the plant. They are the simplest type of terpenes that are composed of two isoprene units. It’s been speculated that a common monoterpene like myrcene helps THC traverse the blood-brain barrier and gives some strains their potency. The opiate antagonist naloxone (Narcan) counteracts the analgesic effects of myrcene, indicating that the analgesic benefits of myrcene are related to interactions with the opiate system. In general, strains with a high myrcene content tend to have sedative effects.