Letrozole vs RAD-140
FDA Approved vs Emerging
avoid Mechanism-based · 53% Both Letrozole and RAD-140 carry hepatotoxic risk. Combining hepatotoxic compounds significantly increases liver damage potential. If unavoidable, include liver support (TUDCA/NAC) and monitor ALT/AST frequently.
Molecular Data
Letrozole RAD-140
Weight 285.30 Da 393.83 Da
Half-life ~2 days (48 hours) ~60 hours
Type Nonsteroidal aromatase inhibitor (triazole derivative) Nonsteroidal selective androgen receptor modulator (C20H16ClN5O2)
Key Benefits
Letrozole
01 Most potent aromatase inhibitor available, achieving ~98% estradiol suppression at medical doses
02 Effective rescue compound for acute gynecomastia flare-ups unresponsive to other AIs
03 Capable of managing estrogen on very high aromatizing cycles where anastrozole is insufficient
04 Oral dosing with a 2-day half-life supports every-other-day scheduling
05 Well-characterized pharmacokinetics with extensive clinical data from breast cancer treatment
06 Reversible inhibition allows estrogen recovery after discontinuation
07 FDA-approved with decades of safety and efficacy data
RAD-140
01 Potent anabolic activity in muscle tissue with high oral bioavailability
02 Tissue-selective action sparing the prostate and other androgen-sensitive organs
03 No aromatization to estrogen (no estrogen-related side effects such as water retention or gynecomastia)
04 No conversion to DHT (reduced risk of hair loss and prostate stimulation compared to testosterone)
05 Long half-life (~60 hours) permitting convenient once-daily oral dosing
06 Neuroprotective properties observed in preclinical models
07 Increased lean body mass and reduced fat mass in preclinical studies
Side Effects
Letrozole
Severe joint pain, stiffness, and dryness (the hallmark side effect of aggressive estrogen suppression)
Fatigue and profound lethargy
Mood disturbance (depression, emotional flatness, irritability)
Decreased libido and sexual dysfunction
Hot flashes or flushing
Headache
Muscle aches and generalized pain
RAD-140
Testosterone suppression (dose-dependent, occurs in virtually all users by week 4-6)
Liver enzyme elevation (ALT, AST increases reported in clinical and anecdotal data)
Hair shedding (temporary, typically resolves after discontinuation)
Headaches (most common in the first 1-2 weeks, often transient)
Nausea (mild, usually with initial doses or on an empty stomach)
Lipid disruption (HDL suppression, LDL elevation)
Mild insomnia or sleep disturbance
Reduced libido and mood changes related to testosterone suppression
Contraindications
Known hypersensitivity to letrozole or any excipients
Premenopausal women (unless under specialist care for fertility treatment)
Pregnancy or breastfeeding (teratogenic risk -- letrozole is Category X)
Severe hepatic impairment
Pre-existing severe osteoporosis or high fracture risk
History of estrogen-crash-related adverse events with prior AI use
Pre-existing liver disease or elevated liver enzymes at baseline
Hormone-sensitive cancers (prostate cancer, certain breast cancers not being treated under clinical supervision)
Pregnancy or potential pregnancy (teratogenic risk from androgen receptor agonism)
Breastfeeding
Age under 25 (incomplete endocrine system maturation and higher risk of HPG axis disruption)
Concurrent use of hepatotoxic medications without medical supervision
Known cardiovascular disease (insufficient safety data for this population)
Research Evidence
Letrozole RAD-140
Status FDA Approved Emerging
References 5 studies 5 studies
Latest — July 2020
FDA Approved Yes No
This comparison is for educational and research purposes only. Consult a healthcare professional before use.