According to drugs.com, there has been little research conducted on the possible negative effects of smoking parsley; however, smoking dried parsley may produce euphoria or even act as an aphrodisiac.
Drugs.com notes that parsley has been historically used in the treatment of prostate, liver and spleen diseases, as well as, anemia, arthritis and microbial infections. It has also been used as a diuretic and laxative. As a fresh or dried herb, parsley and parsley flakes provide calcium, iron and vitamin C. There are few known clinical trials on the effects of parsley. According to drugs.com, reported adverse effects of ingesting concentrated parsley oil include: headache, giddiness, loss of balance, convulsions and renal damage.