Scientific research has found  that deep-slow breathing can reduce blood pressure without the use of drugs.  A temporary reduction in blood pressure can occur almost immediately, while a cumulative long lasting reduction in blood pressure can occur with repeated sessions of deep-slow breathing.  Deep breathing is safe for healthy people.  Persons with serious health conditions should consult their physician before doing breathing exercises.

Scientific Studies:

Breathing-control lowers blood pressure. Grossman E., Grossman A., Schein M.H., Zimlichman R., Gavish B. Journal of Human Hypertension 2001; 15:263-269.

Slow breathing reduces chemoreflex response to hypoxia and hypercapnia, and increases baroreflex sensitivity. Bernardi L, Gabutti A, Porta C, Spicuzza L. J Hypertens. 2001 Dec;19(12):2221-9. PMID: 11725167 [PubMed - indexed for MEDLINE] 

Controlled breathing protocols probe human autonomic cardiovascular rhythms. Cooke WH, Cox JF, Diedrich AM, Taylor JA, Beightol LA, Ames JE 4th, Hoag JB, Seidel H, Eckberg DL. Am J Physiol. 1998 Feb;274(2 Pt 2):H709-18. PMID: 9486278 [PubMed - indexed for MEDLINE]

Slow breathing increases arterial baroreflex sensitivity in patients with chronic heart failure. Bernardi L, Porta C, Spicuzza L, Bellwon J, Spadacini G, Frey AW, Yeung LY, Sanderson JE, Pedretti R, Tramarin R. Circulation. 2002 Jan 15;105(2):143-5. PMID: 11790690 [PubMed - indexed for MEDLINE] 

Respiration and Blood Pressure. Parati G, Izzo JL Jr, Gavish B., in Hypertension Primer, Third Edition. JL Izzo and HR Black, Eds. Baltimore, Lippincott, Williams, and Wilkins, 2003; Ch. A40, p117-120.