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Vampire Steroids "Alive" at Night

Ashley Kersten, PharmD Intern and Jennifer K. Seltzer, PharmD

October 14, 2013

Vampires are appearing in more than just blockbuster films and TV shows; scientists recently discovered a "vampire steroid" that may be attacking some United States water supplies.

Trenbolone is an anabolic steroid used in cattle feed across the country. This product was originally believed to undergo phototransformation and break down in the presence of sunlight. However, new research has found that night-time conditions in rivers and lakes (25◦C and pH 7) facilitate reassembly of the parent compound.1, 2

While human trenbolone use is banned, the substance is frequently abused by bodybuilders. Structurally, trenbolone is similar to tetrahydrogestrinone (THG). THG is undetectable on routine urine screens because the heat and chemicals used in the drug screen process cause the substance to degrade. THG was the center of a large scandal in the early 2000s when dozens of professional athletes, including Barry Bonds, were allegedly abusing the substance.

Trenbolone metabolites are potent endocrine-disrupting compounds that interfere with important signaling pathways, especially in fetal and early life development. In humans, anabolic steroids can cause stunted growth, kidney damage, hypertension, increased hair growth in females and infertility in males.4 Evidence suggest these metabolites damage the reproductive cycle of several species of fish.2

Steroid hormones and prescription drugs are currently found in more than 50% of surface water  sources for drinking.3 The product-to-parent reversion of trenbolone means steroid levels in the water supply could be grossly underestimated as tests to evaluate its presence are usually conducted  during the day. Throughout a 72-hour night-day cycle, researchers found degradation of trenbolone in daylight hours followed by an equivalent rate of regeneration during the dark period.2 

While researchers do not believe there is an immediate risk for humans, there are concerns over the true amount of steroid contaminating drinking water. Better environmental control policies should be considered, such as chemical monitoring over a 48-hour period. The Food and Drug Administration and Environmental Protection Agency have not commented on the discovery.



  1. Weller C. Vampire steroid could threaten water supply: how does trenbolone reawaken in the absence of sunlight? Medical Daily. 27 Sept. 2013. Available at:  Accessed  Oct 9, 2013.
  2. Qu S, Kolodzief EP, Long SA, et al. Product-to-parent reversion of trenbolone: unrecognized risks for endocrine disruption. Science. [DOI:10.1126/science.1243192] Epub ahead of print 2013 Sept 26.
  3. Kolpin DW, Furlong ET, Meyer MT, et al. Pharmaceuticals, hormones, and other organic wastewater contaminants in U.S. streams, 1999 2000: a national reconnaissance. Environ Sci Technol. 2002 Mar 15;36(6):1202-11.
  4. McNeil DG. Drug testing; acting quickly, U.S. bans newfound steroid. The New York Times. October 29, 2003. Available at: Accessed October 11, 2013.

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