Mirabegron (Myrbetriq)
Selective β3-adrenergic receptor agonist. Originally approved for overactive bladder (Astellas, brand name Myrbetriq). Increasingly used in fat-loss protocols for its ability to activate brown adipose tissue (BAT) thermogenesis without the β2-driven cardiac and tremor side effects of [Clenbuterol](/compounds/other-compounds/clenbuterol).
Overview
Selective β3-adrenergic receptor agonist. Originally approved for overactive bladder (Astellas, brand name Myrbetriq). Increasingly used in fat-loss protocols for its ability to activate brown adipose tissue (BAT) thermogenesis without the β2-driven cardiac and tremor side effects of [Clenbuterol](/compounds/other-compounds/clenbuterol).
Activates brown adipose tissue thermogenesis, increases resting energy expenditure (~200 kcal/day at clinical doses), promotes browning of white adipose tissue, improves insulin sensitivity (BAT glucose uptake), may modestly improve HDL cholesterol. Mild blood pressure elevation, mild heart rate increase, urinary retention risk, dry mouth. No suppression of HPTA. No direct impact on liver enzymes at standard doses.
Compound Guide
Mechanism: Selective β3-adrenergic receptor agonist. β3 receptors are concentrated in brown adipose tissue (BAT), the urinary bladder detrusor muscle, and the gallbladder. Activation increases cAMP in BAT, driving UCP1 (uncoupling protein 1) expression, which generates heat by uncoupling mitochondrial oxidative phosphorylation. Distinct from Clenbuterol, which is β2-selective and acts primarily on muscle and bronchial smooth muscle.
Dosage:
- Bladder indication (approved): 25-50mg/day oral
- Fat-loss bodybuilding use: 50-100mg/day oral, single morning dose
- Advanced/anecdotal: 150-200mg/day (substantially higher BP/HR risk, off-label, not validated)
- Cycle: 4-12 weeks, monitor BP throughout; no clear receptor downregulation issue (unlike clenbuterol)
Administration:
- Oral, once daily. Extended-release formulation — do not crush or split tablets
- Morning dosing preferred (slight stimulation can affect sleep)
- Can be taken with or without food (high-fat meal slightly reduces Cmax but does not affect total exposure)
Key Notes:
- Not an anabolic steroid — no impact on testosterone, estradiol, LH/FSH
- Primary fat-loss mechanism is thermogenic, NOT appetite suppression — pairs well with GLP-1 agonists for combined fat-loss protocols
- Cleaner side effect profile than clenbuterol: minimal tremor, no muscle cramps, no taurine depletion, much milder tachycardia
- BAT activation is potentiated by cold exposure — some users combine with cold showers / ice baths
- Long half-life (~50 hours) means steady-state plasma levels — different feel than clenbuterol's spike-then-crash kinetics
- BP elevation is mild but real at higher doses — average +3-4 mmHg systolic at 50mg/day; can be larger in salt-sensitive individuals
- Inhibits CYP2D6 (moderate) — caution with metoprolol, tramadol, codeine, some SSRIs
- Urinary retention risk in men with BPH — caution with concurrent anticholinergics or alpha-blocker users
- Rare: angioedema (typically face/lips/tongue within 24-48h of first dose)
- Cardiovascular: monitor BP weekly during titration, avoid if uncontrolled hypertension
- Pairs well with: caffeine (additive thermogenesis), cold exposure, low-dose semaglutide, healthy lipid intake
- Bodybuilding relevance: contest prep fat loss without clenbuterol side effects, recomposition phase, breaking through plateaus on a cut
- Monitor: blood pressure, resting heart rate, lipid panel (HDL often improves), fasting glucose / HbA1c (insulin sensitivity often improves), ECG if used >8 weeks at high dose
Usage History
Frequently Asked Questions
Quick Reference
Category
Other
Half-Life
~50 hours
Detection Time
N/A