Rapamycin (Sirolimus) vs Tirzepatide

Mechanism

Rapamycin binds the intracellular protein FKBP12, and the rapamycin-FKBP12 complex inhibits mechanistic target of rapamycin complex 1 (mTORC1), a serine/threonine kinase that integrates nutrient sensing, growth factor signaling, and cellular energy status. mTORC1 inhibition suppresses S6K1-mediated ribosomal protein synthesis, activates ULK1-mediated autophagy and mitophagy, enhances lysosomal biogenesis via TFEB nuclear translocation, reduces senescent cell accumulation, and suppresses the SASP (senescence-associated secretory phenotype). At higher chronic doses, rapamycin also inhibits mTORC2, which regulates Akt-mediated insulin signaling — this is believed to drive the metabolic side effects.

Standard Dosing

Research indicates 5-6 mg once weekly (intermittent/pulsed dosing) for longevity protocols. This weekly pulsed approach preferentially inhibits mTORC1 while allowing mTORC2 to remain functional.

Timing

Once weekly, consistent day each week. Take with or without food (food increases bioavailability by ~35% — be consistent either way). Grapefruit juice significantly increases rapamycin bioavailability via CYP3A4 inhibition — some practitioners use this intentionally to reduce pill burden.

Cycle Duration

Long-term (years) for longevity applications. The PEARL trial assessed up to 12 months of treatment in healthy older adults.

Side Effects

• Mouth ulcers/canker sores (most common, dose-dependent)
• Elevated lipids (triglycerides and LDL — typically manageable with weekly dosing)
• Impaired wound healing
• Mild immunosuppression (increased susceptibility to infections)
• Insulin resistance (primarily from mTORC2 inhibition at higher/daily doses)
• Acne-like skin eruptions
• Thrombocytopenia and leukopenia (rare at longevity doses)

Contraindications

• Active infections (immunosuppression risk)
• Poorly healing wounds or planned surgery (delays wound healing)
• Severe hepatic impairment
• Uncontrolled hyperlipidemia
• Pregnancy and breastfeeding
• Organ transplant patients on calcineurin inhibitors (specialized dosing required)
• Active infection
• Immunocompromised states
• Poorly controlled diabetes
• Wound healing (pause 2 weeks pre-surgery)

Best Stacking Partners

Mechanism

Dual GIP/GLP-1 receptor agonist. Enhances insulin secretion, reduces glucagon, slows gastric emptying, and acts on hypothalamic appetite centers. Produces greater weight loss than semaglutide in head-to-head trials. Also improves cardiovascular risk markers.

Contraindications

• Personal/family history of medullary thyroid carcinoma
• MEN2 syndrome
• Pancreatitis history
• Severe GI disease