Longevity Prescriptions: What Actually Has Evidence

What "Longevity Medicine" Actually Means

Longevity medicine targets two distinct but overlapping goals: extending lifespan (total years lived) and extending healthspan (years lived free from major chronic disease). Most clinicians now focus primarily on healthspan, because the interventions with the strongest evidence reduce cardiovascular events, metabolic disease, and functional decline rather than directly adding calendar years.

The field divides roughly into three mechanistic categories. The first covers compounds that reduce known all-cause mortality drivers: cardiometabolic disease, cancer, and neurodegeneration. The second covers compounds that modulate conserved aging pathways (mTOR, AMPK, sirtuins, NAD+ metabolism). The third covers hormone replacement, which addresses the steep decline in anabolic and cardioprotective hormones that begins in the fourth decade of life.

Why Most "Anti-Aging" Headlines Are Misleading

Most animal-model results do not replicate in humans. Rapamycin extends lifespan in every model organism tested, but human RCT data in healthy adults remain sparse. Resveratrol generated enormous excitement after a 2006 Nature paper; later trials showed no meaningful human benefit at achievable oral doses. Evidence grades in this article follow the GRADE system used by the American College of Endocrinology.

The Hallmarks of Aging Framework

The 2023 update to the Hallmarks of Aging paper (Lopez-Otin et al., Cell 2023) now lists 12 hallmarks, including genomic instability, telomere attrition, epigenetic alterations, mitochondrial dysfunction, and chronic inflammation (PubMed). Every prescription discussed below maps to at least one of these hallmarks. Understanding which hallmark a drug targets helps predict combination when stacking protocols.

Metformin: The Strongest Off-Label Case

Metformin (biguanide, generic, FDA-approved for type 2 diabetes) is the single longevity compound with the most human observational data and the only one that has secured FDA approval for a dedicated longevity trial (TAME).

TAME Trial and Observational Evidence

The Targeting Aging with Metformin (TAME) trial (N=3,000, 14 U.S. Sites, primary endpoint: composite of incident chronic disease and death) is actively enrolling adults aged 65 to 79 with no diabetes diagnosis. The trial design was published in Cell Metabolism in 2023 (PubMed). Observational data from the UK Biobank (N=180,000+) showed that diabetic patients on metformin had lower all-cause mortality than age-matched non-diabetic controls not on metformin (PubMed).

Mechanism

Metformin activates AMPK, which inhibits mTORC1 signaling, reduces mitochondrial complex-I activity, and lowers hepatic glucose output. These actions overlap with caloric restriction mimicry. It also reduces circulating IGF-1 and has demonstrated senolytic-adjacent effects in preclinical models.

Dosing and Monitoring

Off-label longevity dosing typically runs 500 mg twice daily with meals, titrated to 1,000 mg twice daily. Serum creatinine (eGFR <30 is a contraindication), vitamin B12 levels annually, and HbA1c every 6 months are the minimum monitoring requirements. GI side effects affect roughly 25% of patients at initiation; extended-release formulations cut this rate to approximately 10%.

GLP-1 Receptor Agonists: Cardiovascular and Weight Data Are Compelling

GLP-1 receptor agonists (semaglutide, tirzepatide, liraglutide) have moved from diabetes drugs to the most evidence-dense class of agents for reducing two of the biggest longevity killers: cardiovascular disease and obesity.

SELECT Trial: The Landmark Data Point

The SELECT trial (N=17,604, adults with overweight/obesity and established cardiovascular disease, no diabetes) showed that semaglutide 2.4 mg weekly reduced major adverse cardiovascular events (MACE) by 20% versus placebo over a median of 33.3 months (HR 0.80, 95% CI 0.72 to 0.90, P<0.001) (NEJM). This was the first large cardiovascular outcomes trial in a non-diabetic population for a GLP-1 agent.

Weight Loss and Its Downstream Effects

STEP-1 (N=1,961) showed semaglutide 2.4 mg produced 14.9% mean body weight loss at 68 weeks versus 2.4% for placebo (NEJM). SURMOUNT-1 (N=2,539) showed tirzepatide 15 mg produced up to 22.5% weight loss at 72 weeks (NEJM). Reducing excess adiposity directly lowers risk of type 2 diabetes, hypertension, sleep apnea, and several obesity-linked cancers, all of which compress healthspan.

Emerging Data on Neurodegeneration

A 2024 observational study in JAMA Neurology (N=1,649 GLP-1 users vs. Propensity-matched controls) found a 40 to 70% lower incidence of Alzheimer's disease in patients on GLP-1 agonists at 3-year follow-up (PubMed). RCTs specifically targeting cognitive outcomes are underway but not yet complete. This signal is hypothesis-generating, not practice-changing on its own.

Rapamycin (Sirolimus): High Potential, Limited Human Data

Rapamycin (mTOR inhibitor, FDA-approved for transplant rejection and certain cancers) is the compound that extends lifespan most consistently across every animal model tested, from yeast to primates. The question is whether that translates to healthy humans.

Animal Model Evidence

The Interventions Testing Program (ITP), funded by the National Institute on Aging, showed rapamycin extended median lifespan in genetically heterogeneous mice by 9 to 14% even when started at 20 months of age (equivalent to roughly age 60 in humans) (PubMed). The ITP has tested over 40 compounds; rapamycin is one of the few with strong, replicated results.

Human Evidence: What Exists

A 2014 trial by Mannick et al. (N=218 adults aged 65+) used RAD001 (everolimus, a rapamycin analog) at low doses and found a 20% improvement in response to influenza vaccine at 6 weeks, suggesting improved immune function (Science Translational Medicine). No human RCT has yet demonstrated lifespan extension. The PEARL trial (NCT04488016) is ongoing in healthy adults.

Dosing and Risk Profile

Clinicians who prescribe off-label rapamycin for longevity typically use 1 to 6 mg once weekly (intermittent dosing to reduce immunosuppression). Side effects at daily transplant doses (2 to 5 mg/day) include impaired wound healing, hyperlipidemia, and infection risk. Weekly dosing appears to attenuate these risks based on pharmacokinetic modeling, but no head-to-head safety trial in healthy adults exists yet.

Hormone Replacement: Testosterone and Estrogen

Hormone levels decline predictably with age. Testosterone in men drops approximately 1 to 2% per year after age 30. Estradiol in women drops sharply at menopause, typically in the early 50s. Both declines associate with worse cardiometabolic outcomes, reduced muscle mass, cognitive decline, and reduced bone density.

Testosterone Replacement Therapy in Men

The TRAVERSE trial (N=5,246 hypogonadal men, aged 45 to 80, with elevated cardiovascular risk) showed testosterone replacement therapy (TRT) did not increase MACE risk versus placebo (HR 0.96, 95% CI 0.78 to 1.17) over a mean 33-month follow-up (NEJM). A pre-specified secondary analysis found TRT reduced new-onset type 2 diabetes by 32% in those with prediabetes at baseline. The 2023 American Urological Association guideline defines hypogonadism as total testosterone <300 ng/dL on two morning measurements (American Urological Association).

Monitoring includes hematocrit (target <54%), PSA, and total/free testosterone every 6 to 12 months. Erythrocytosis (hematocrit >54%) is the most common dose-limiting side effect.

Estrogen Replacement in Women

The Women's Health Initiative (WHI) original 2002 publication generated widespread fear about HRT. Re-analysis of the WHI data stratified by age at initiation showed that women who started conjugated equine estrogen within 10 years of menopause had approximately 50% lower coronary heart disease risk versus those starting more than 10 years post-menopause, establishing what is now called the "timing hypothesis" (PubMed). The 2022 Menopause Society (NAMS) position statement states: "For women aged younger than 60 years or within 10 years of menopause onset without contraindications, the benefit-risk ratio is favorable for treatment of bothersome vasomotor symptoms and for prevention of bone loss and fracture." (Menopause Society).

Bioidentical estradiol (transdermal patch or gel) and micronized progesterone are preferred over oral conjugated equine estrogen due to lower venous thromboembolism risk with transdermal delivery (PubMed).

NAD+ Precursors: NMN and NR

Nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) raise intracellular NAD+ levels. NAD+ declines roughly 50% between ages 40 and 60 in human tissue samples. NAD+ is required for sirtuin activity, DNA repair, and mitochondrial function, three hallmarks of aging.

What the Human Trials Show

A 12-week randomized, double-blind, placebo-controlled trial (N=30 healthy men aged 65+) showed NMN 250 mg/day raised blood NAD+ levels by approximately 38% versus placebo and improved gait speed and grip strength (PubMed). A separate 60-day trial of NR 1,000 mg/day in older adults (N=12) showed a 60% rise in blood NAD+ but no significant change in metabolic markers (PubMed). Effect sizes in NAD+ trials remain modest and sample sizes small. This is a promising category with insufficient Phase 3 data.

Dosing Considerations

NMN is typically dosed at 500 to 1,000 mg/day in two divided doses. NR is dosed at 300 to 1,000 mg/day. Neither has an established drug interaction profile with rapamycin or metformin. Combining NAD+ precursors with mTOR inhibitors may theoretically produce antagonistic effects on sirtuin-AMPK crosstalk, a concern raised in a 2021 review in Nature Aging but not yet tested in human trials (PubMed).

Acarbose and Low-Dose Naltrexone: Tier 2 Options

Acarbose

Acarbose (alpha-glucosidase inhibitor, FDA-approved for type 2 diabetes) extended median lifespan in male ITP mice by 22% and female mice by 5% at 1,000 ppm in chow (PubMed). The sex difference appears related to differential absorption kinetics. Human longevity trials are absent; acarbose is occasionally used off-label to blunt postprandial glucose spikes. Dose: 25 to 100 mg before meals. GI flatulence affects the majority of users.

Low-Dose Naltrexone

Low-dose naltrexone (LDN, 1.5 to 4.5 mg nightly, well below the 50 mg FDA-approved addiction dose) shows immunomodulatory effects via transient opioid receptor blockade and glial TLR4 antagonism. A 2023 systematic review in Frontiers in Pharmacology identified 22 clinical studies showing benefit in inflammatory and autoimmune conditions (PubMed). No human longevity RCT exists. It fits the longevity framework by targeting chronic low-grade inflammation (inflammaging), but remains speculative for lifespan outcomes.

Evidence Comparison Table

| Compound | Best Human Evidence | Evidence Grade | Longevity Mechanism | Primary Risk | |---|---|---|---|---| | Metformin | TAME trial (ongoing), UK Biobank | B (observational) | AMPK/mTOR, glucose | B12 deficiency, GI | | Semaglutide 2.4 mg | SELECT (N=17,604), STEP-1 | A (RCT) | CV risk, weight | Nausea, pancreatitis risk | | Tirzepatide 15 mg | SURMOUNT-1 (N=2,539) | A (RCT) | CV risk, weight | Nausea, GI | | Testosterone (TRT) | TRAVERSE (N=5,246) | A (RCT) | Metabolic, muscle | Erythrocytosis | | Estrogen (HRT) | WHI re-analysis, KEEPS | B (post-hoc RCT) | CV, bone, cognition | DVT (oral route) | | Rapamycin | ITP mice; Mannick 2014 (N=218) | C (animal + small RCT) | mTOR inhibition | Immune, lipids | | NMN/NR | Small RCTs (N=12 to 30) | C (small RCT) | NAD+/sirtuins | Unknown long-term | | Acarbose | ITP mice; no human longevity RCT | D (animal only) | Glucose blunting | Flatulence | | Low-dose naltrexone | Inflammatory disease trials | C (small RCT) | Inflammaging | Sleep disruption |

Evidence grades: A = large RCT; B = smaller RCT or strong observational; C = small RCT or animal with human plausibility; D = animal/mechanistic only.

Who Should Not Use These Compounds

Blanket contraindications vary by compound, but several patterns apply across the longevity stack.

Metformin: Contraindicated with eGFR <30 mL/min/1.73m2, active heart failure requiring pharmacologic treatment, and iodinated contrast administration within 48 hours. Relative caution with eGFR 30 to 45.

GLP-1 agonists: Contraindicated with personal or family history of medullary thyroid carcinoma or MEN2. Use with caution in patients with gastroparesis. Not approved in pregnancy.

Rapamycin: Avoid in patients with active or recent bacterial/fungal infection, poorly controlled diabetes (impairs wound healing), or active malignancy under immunotherapy.

TRT: Contraindicated in men with breast or prostate cancer, hematocrit >54% at baseline, or plans for fertility (suppresses spermatogenesis; hCG co-treatment partially mitigates this).

HRT (estrogen): Contraindicated with active or recent venous thromboembolism, estrogen-sensitive breast cancer, or active liver disease. Transdermal delivery largely bypasses hepatic first-pass and carries substantially lower DVT risk than oral formulations (PubMed).

Monitoring Protocol for a Longevity Stack

Patients taking one or more of these compounds require structured monitoring. The following schedule reflects standard-of-care minimums for each class.

Baseline Workup (Before Starting Any Protocol)

Every patient should have: comprehensive metabolic panel (CMP), complete blood count (CBC), fasting lipid panel, HbA1c, fasting insulin, hsCRP, homocysteine, full hormone panel (testosterone total and free, SHBG, estradiol, DHEA-S, IGF-1, TSH, free T4), DEXA scan for body composition, and coronary artery calcium (CAC) scoring for those over 40 with any cardiovascular risk factors.

Ongoing Monitoring

• Every 3 months (first year): HbA1c, CMP, CBC, weight, blood pressure
• Every 6 months: Full hormone panel, lipid panel, hsCRP
• Annually: DEXA, PSA (men on TRT), mammogram (women on HRT), B12 (metformin users), ophthalmology if diabetic risk present

Adjustments to any compound should be made by a licensed prescriber, not self-managed based on consumer lab kits alone.

When to Consider a Longevity Protocol

Age alone is not a sufficient criterion. The patients most likely to benefit from a structured longevity protocol share a specific risk profile.

Strong indications include: age 40+, at least one metabolic risk factor (prediabetes, dyslipidemia, hypertension, elevated hsCRP >2.0 mg/L), BMI >27 with visceral adiposity on DEXA, or documented hormonal deficiency (testosterone <300 ng/dL in men, symptomatic perimenopause in women). Patients with a CAC score above zero have a 10-year MACE risk high enough to justify cardiovascular-targeted GLP-1 therapy independent of weight status, per the 2023 ACC/AHA cholesterol guidelines (ACC/AHA via AHAJournals).

A 40-year-old with normal metabolic labs, no hormone deficiency, and BMI <25 does not yet meet the threshold for most prescription interventions. Lifestyle optimization (resistance training, Zone 2 cardio, sleep 7 to 9 hours, Mediterranean diet) has a larger effect size at that baseline than any single drug.

Stacking Protocols: What Can Be Combined

Several combinations appear synergistic at the mechanistic level.

Metformin plus NMN has been questioned because a 2023 trial (N=60) found metformin partially blunted the muscle-mass-preserving effect of exercise in older adults, possibly by interfering with AMPK-mitochondrial biogenesis (PubMed). Some longevity clinicians therefore time metformin away from exercise windows (take at dinner rather than pre-workout). GLP-1 agonists combine safely with TRT or HRT with no known pharmacokinetic interaction. Rapamycin combined with metformin is the stack with the strongest animal-model data for additive lifespan extension, but human safety data for healthy adults on both compounds simultaneously does not yet exist.

Any stack should be supervised by a physician familiar with the interaction profiles of each agent. Self-assembly of longevity stacks based on podcasts or social media carries real risks of additive immunosuppression, erythrocytosis, or metabolic disruption.