Effects and adverse effects of ibutamoren

Ibutamoren (MK-677) has been researched with aims of increasing muscle mass, improving healing of injures and increasing quality of sleep. But there are also some side-effects related to blood pressure.

Growth hormone deficiency, if present, is associated with lower blood pressure independent of the time of the day [1] with normal response to exercise in humans. In rats whose hypophysis (part of brain that produces growth hormone) was removed, growth hormone lowered blood pressure, instead [2]. Mechanistically, alterations of growth hormone level may modify the blood pressure indeed but the exact dose relationship is unknown, and human studies must be considered more informative.

Growth hormone release amplifier MK-677 or ibutamoren is also relevant from the perspective of cardiovascular health: a study with obese humans has shown that ibutamoren moderately but significantly increased both diastolic blood pressure (mean 84 vs 79) and heart rate (mean 61 vs 56) [3]. In the first administration of ibutamoren, a transient elevation of prolactin and cortisol was observed, while the long term result was increase of fat free mass[4]. On the other hand, ibutamoren moderately decreased glucose tolerance in the long term, which reduces its potential utility for diabetic (as indicated by elevated glucose levels and glucose intolerance) and pre-diabetic (as indicated by elevated glycosylated hemoglobin levels in blood) humans. The effects of ibutamoren may be dependent on age and duration of administration. The negative effects may be more prominent in the elderly, as it was associated with congestive heart failure and elevated blood pressure in a study of elderly patients with hip fracture [4]. While there were some improvements in the gait speed and prevention of falling, the study was terminated early due to this side effect.

[1] https://www.ncbi.nlm.nih.gov/pubmed/11282052
[2] https://www.ncbi.nlm.nih.gov/pubmed/15525587
[3] https://academic.oup.com/jcem/article/83/2/362/2865156
[4] https://www.ncbi.nlm.nih.gov/pubmed/21067829