YK-11

YK-11 binds to the androgen receptor with high affinity and induces expression of follistatin, a protein that directly antagonizes myostatin. Myostatin is a negative regulator of muscle growth; by blocking it, YK-11 removes the natural ceiling on muscle hypertrophy. Additionally, YK-11 promotes bone mineralization by activating protein kinase B (Akt) signaling, which may enhance bone density. Its partial agonist activity at the androgen receptor means it stimulates anabolic pathways without full androgenic activation.

YK-11 is rapidly absorbed orally with peak plasma levels reached in approximately 1-2 hours. It undergoes hepatic metabolism and has a half-life of approximately 6-10 hours, necessitating split dosing. Due to its steroidal structure (DHT derivative), it is methylated and passes through the liver, which means some degree of hepatotoxicity is possible with extended use. It does not aromatize to estrogen.

• ✓Significant lean muscle mass gains (4-8 lbs in an 8-week cycle is common)
• ✓Myostatin inhibition removes the genetic ceiling on muscle growth
• ✓Increased follistatin production
• ✓Enhanced bone mineral density through Akt signaling
• ✓Does not aromatize to estrogen, so no water retention or gynecomastia from estrogenic activity
• ✓Strength gains reported within the first 2-3 weeks
• ✓Potential benefit for stubborn muscle groups that resist growth

• ⚠Suppression of natural testosterone production (moderate to significant)
• ⚠Potential liver stress due to methylated steroidal structure (monitor liver enzymes)
• ⚠Joint dryness at higher doses (due to DHT-derived nature and lack of estrogenic activity)
• ⚠Mild hair shedding in those predisposed to male pattern baldness
• ⚠Potential aggression or mood changes at higher doses
• ⚠Fatigue and lethargy toward the end of cycle if testosterone suppression is significant
• ⚠Limited long-term human safety data

Contraindications

• 🚫Pre-existing liver disease or elevated liver enzymes
• 🚫History of hormone-sensitive cancers
• 🚫Women who are pregnant or breastfeeding
• 🚫Individuals under 21 years of age (endocrine system still maturing)
• 🚫Those currently on hepatotoxic medications (oral antibiotics, statins, accutane)
• 🚫Pre-existing cardiovascular conditions with poor lipid profiles

**PCT is required.** YK-11 causes moderate to significant testosterone suppression. **Standard PCT (mild-moderate suppression):** - Nolvadex (Tamoxifen) 20 mg/day for 4 weeks, OR - Clomid 25 mg/day for 4 weeks **Aggressive PCT (significant suppression, confirmed by bloodwork):** - Nolvadex 40/40/20/20 mg over 4 weeks, OR - Clomid 50/50/25/25 mg over 4 weeks Begin PCT the day after your last dose of YK-11 (due to short half-life). Recheck bloodwork 4 weeks after completing PCT to confirm recovery.

• 1.Always split the dose AM/PM for stable blood levels
• 2.Run a liver support supplement (NAC 600-1200 mg/day, TUDCA 250-500 mg/day) throughout the cycle
• 3.Keep cycles to 8 weeks maximum; 6 weeks is safer for first-timers
• 4.Have your PCT compounds on hand BEFORE starting the cycle
• 5.YK-11 stacks exceptionally well with non-methylated SARMs like RAD-140 or LGD-4033
• 6.Stay well-hydrated and keep sodium moderate to manage any joint dryness
• 7.Get bloodwork done at baseline, mid-cycle (week 4), and 4 weeks post-PCT
• 8.If you experience significant lethargy or dark urine mid-cycle, get liver enzymes checked immediately

1. [1]Kanno Y, et al. (2011). Selective androgen receptor modulator, YK11, regulates myogenic differentiation of C2C12 myoblasts by follistatin expression. Biol Pharm Bull.
2. [2]Yatsu T, et al. (2018). Selective Androgen Receptor Modulator, YK11, Up-Regulates Osteoblastic Proliferation and Differentiation in MC3T3-E1 Cells. Biol Pharm Bull.