A toxicity study in rats fed up to five percent HMB in the diet was conducted. The data showed that HMB at five percent of the diet can be considered the NOAEL (no observed adverse effect level). The intakes were 3.49 and 4.16 g HMB/kg body weight per day in male and female rats, respectively. (Like a normal human consuming about 300 g per day)
In this eight-week double-blind, randomized study with male weightlifters consuming up to six grams of HMB per day was shown to have no adverse effects on measures of hematology and hepatic and renal function.
This study reported a summary of safety data from nine double-blind, placebo-controlled, randomized clinical trials including both men and women and young and elderly adults. HMB supplementation was shown to have no adverse or untoward effects. HMB supplementation was also shown to have positive effects on LDL cholesterol (-7.3 percent) and systolic blood pressure (-4.4 mm Hg).