Donald Kennedy was a Patent Medicine Manufacturer in Roxbury, Mass. from around 1848 to the late 1880s. In the 1850s when he needed a national distributor he selected Charles H. Ring (see Ring's Ambrosia). The business address in 1854 was at 120 Warren Street.
By 1876, George Kennedy had joined him in the business. According to the Wilsons, he opened a central distributing depot in Boston that year. It is likely that George was one of Donald's sons.
The Hair Tea (Oil of Tea) was described in John F. Henry catalogs as "an unequaled promoter of the growth and beauty of the hair" in 1872, and "A vegetable Tonic & preserver of the Hair" in 1880. The first reference to the Hair Tea I found was an ad in an 1871 Harper's Weekly. The last time I found it for sale was in the 1885 McKesson & Robbins catalog.
In the 1875 John F. Henry catalog, the Hair Grower was said to "cure scaly eruptions on the head, and covers bald spots with Hair." Another ad in the 1885 McKesson & Robbins catalog said it was "for scald head & loss of hair from dandruff & heat." The earliest listing of the Hair Grower I've found was in the 1872 Henry catalog. The last reference I found to the product was in the 1901 Morrison & Plummer catalog.