The plant source is Prunus spinosa.  It is blackthorn (Rosaceae) or Pruni
spinosae flos.
The constituents are quercetin and kaempferol glycosides, including quercitrin,
rutin, and hyperoside.
Only in folk medicine, it is used as a mild laxative, diuretic, diaphoretic, and
expectorant; and in homoeopathy for "cardiac weakness" and "nerve pains in the
head."
No side effects in normal doses are to be expected.
No elixir form is listed, although the syrup and wine is used as a purgative and
diuretic.
No breastfeeding benefits are listed.
Since the activity has not been adequately substantiated, therapeutic use cannot
be recommended.

Frank J. Nice, DPA, CPHP