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Alpha-adrenergic Blocking Agents

Ma Huang —Possible Harmful Interaction Yohimbine —Possible Harmful Interaction Quercetin—Possible Harmful Interaction
Alpha-adrenergic blocking agents (or alpha-1 blockers) help smooth muscle relax. This can help to open blood vessels and improve blood flow. It can be part of a treatment plan for high blood pressure. It may also be used to ease urinary retention with BPH (benign prostatic hyperplasia).
Drugs in this category include:
  • Terazosin (Hytrin)
  • Doxazosin (Cardura)
  • Prazosin (Minipress)
  • Alfuzosin (Uroxatral)
  • Silodosin (Rapaflo)
  • Tamsulosin (Jalyn - combination of dutasteride and tamsulosin)
Ma Huang
Ma huang is a natural source for ephedrine and pseudoephedrine. It can increase blood pressure. It may counteract the effect of an alpha-1 blocker. It may reduce the effectiveness of the drug. 1,2
Yohimbine increases blood pressure. This may decrease the effects of an alpha-1 blocker.1,3
Quercetin may be used to manage prostate issues. Tamsulosin can be used to help men with BPH who have urinary flow problems. Since they both have similar effect it may not be wise to combine them. An animal study suggests that combining the two may exaggerate the effect of the drug. 4


Terazosin. EBSCO DynaMed Plus website. Available at: Updated March 6, 2018. Accessed April 11, 2018.
White LM, Gardner SF, Gurley BJ, Marx MA, Wang PL, Estes M. Pharmacokinetics and cardiovascular effects of ma-huang (Ephedra sinica) in normotensive adults. J Clin Pharmacol. 1997;37(2):116-122.
Murburg MM, Villacres EC, Ko GN, Veith RC. Effects of yohimbine on human sympathetic nervous system function. J Clin Endocrinol Metab. 1991;73(4):861-865.
Vrolijk MF, Haenen GR, Opperhuizen A , et al. The supplement-drug interaction of quercetin with tamsulosin on vasorelaxation. Eur J Pharmacol. 2015 Jan 5;746:132-7.

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