Celery has been cultivated as a vegetable since at least the classical Greek and Roman era; it was also found in Tutankhamun's tomb, although that may have been wild celery rather than cultivated.
The medicinal uses of celery seed were first described around AD 30; there are written records of the seeds being used for pain relief. Celery seeds contain phenylpropene, which has in the past been used to treat menstrual disorders.
Celery seeds also contain 3-n-butylphthalide, more commonly known as 3nB, which is a substance known to reduce blood pressure. It does this by acting as both a vasodilator and a diuretic, so it relaxes blood vessels and reduces the volume of blood in the body.
3nB is also thought to have a number of other beneficial effects in the body, including neuro-protective properties. Most attention has been given to 3nB's potential as a pain relieving agent for those suffering from gout and arthritis. A clinical study produced very positive results regarding celery seed extract as pain relief for fibromyalgia.
Celery seed extract is also thought to have anti-anxiety effects when taken as a supplement, although it is not clear how this may work.