Hawthorn (Crataegus species) has a bounty of active constituents to help heal the circulatory system. Among the list of antioxidants is an abundance of oligomeric procyanidins (OPCs). The scientific community has been enthused about this compound as it has anticarcinogenic, anti-inflammatory, antimicrobial, and vasodilatory properties.

To be more precise, OPCs are a group of related compounds which a commonly found in plants. Berries, grape seed, tea, onions, legumes, pine bark, and red wine are often listed as abundant sources. in that list is hawthorn. Usually it is listed as hawthorn herb. This reference can include hawthorn berry (haw or fruit), flower, leaf or all three. The flower and leaf are harvested at the same time in the spring and are sold together. The berry is harvested in the fall and may or may not be added to the flower and leaf mixture to increase the ascorbic acid (vitamin C) content which also decrease inflammation.

The flowers contain a greater amount of other flavonoids. The leaves contain a greater amount of the OPCs. It is currently being speculated that the flavonoids and the OPCs work together to provide antimicrobial protection for the body. One of the flavonoids called polymeric proanthocyanidins (PPCs)  is documented to heal more effectively in conjunction with OPCs than when it is isolated. This is why many naturopathic physicians offer a tincture of both hawthorn leaf and hawthorn flower.

OPCs are noted for stabilizing connective tissue. Connective tissue exists in many places including between the skeletal joints and within the circulatory system of the body. All antioxidants are anti-inflammatory but OPCs focus on connective tissue. For patients with auto-immune diseases, their bodies attack their own connective tissues and trigger inflammation. The OPCs fortify the joints which is why this antioxidant compound is recommended by doctors for reducing the damage of the autoimmune response.