The Astra Learn Library

Evidence-first guides on the treatments people actually ask about. Every research claim carries a numbered citation that resolves to a linked, study-typed reference. Educational, not medical advice.

Longevity

Five reasons you're always tired — Persistent tiredness usually is not one problem. Five of them are measurable: NAD+ falls with age, cells cannot make energy without it, recovery slows, the brain draws on the same supply, and caffeine borrows energy rather than making it.
NAD+ and energy: five reasons — NAD+ is the coenzyme that lets cells turn fuel into usable energy, and it declines with age in measured human samples. Here is the mechanism, the five places it shows up as tiredness, and what the human trials actually found.
Sermorelin — Sermorelin is a fragment of growth hormone-releasing hormone. Instead of injecting growth hormone, it signals the pituitary to release its own, preserving the pulses and feedback loops that direct GH replacement bypasses. The evidence for downstream benefit in healthy aging adults is limited, and the honest reading of the GH-and-aging literature is negative.
Why try NAD+? — People try NAD+ for five reasons that each have real evidence behind them. There is also one honest reason for doubt: raising NAD+ has been much easier to prove than making anyone feel or function better because of it.
Mitochondria and aging — Human muscle biopsies show mitochondrial function declining with age, and longitudinal fitness data shows that decline is not a straight line, it speeds up. Exercise training has changed the trajectory in a controlled trial. Nicotinamide riboside has changed the chemistry of aged muscle without changing the bioenergetics that people actually care about.
The free-radical theory of aging — For decades the dominant idea was that oxidative damage from free radicals drives aging, so neutralizing it with antioxidants should slow aging. Mouse genetics complicated that story, and human antioxidant trials tested it directly and did not support it. The research field moved to mitochondrial quality control instead.
NAD+ vs Glutathione — NAD+ and glutathione get sold side by side on IV drip menus as if they were interchangeable youth boosters. They are not the same molecule, they do not do the same job, and the human evidence behind injecting either of them is thinner than the menu implies.
Biological Age Gap — A consumer test that returns a single number claiming you are 14 years younger than your birth certificate is reporting the output of a research instrument, not a medical verdict. Here is what that instrument actually measures, where it has held up, and where it has not.
Passport 30, Cells 45 — An epigenetic clock can tell you your blood looks older or younger than your birth certificate. In large cohorts that gap tracks with mortality risk. In one person, on one test day, it is a far blurrier signal than the marketing suggests.
Reverse Biological Age — Everyone selling a biological-age fix cites a study. Few explain what kind. Here are five popular interventions, ranked from a very large observational mortality analysis down to a genuine evidence gap, with the population and design named for each.
Female youth at 35 — A number keeps circulating: female youth ends at 35. It borrows real biology, ovarian reserve does decline from before birth, and then stretches it to cover systems it has nothing to do with. Split by system, the picture is slower and less dramatic than the claim.

GLP-1 Therapy

Tirzepatide — Tirzepatide is a dual GIP and GLP-1 receptor agonist. The 72-week SURMOUNT-1 trial in adults with obesity produced the largest average weight reductions yet published for a weekly injectable. This guide covers those numbers, the population they came from, the side effects that come with them, and the regain problem nobody markets.
Microdosing tirzepatide — Microdosing tirzepatide means using doses below the escalation schedule the trials used. The tolerability logic is reasonable and clinicians use it deliberately. The evidence base for it, as a defined protocol with defined outcomes, does not exist. Both of those things are true at once.

Metabolic Support

B12 injections — B12 injections are genuinely necessary for some people and irrelevant for most. The dividing line is absorption, not intake. This guide covers who is actually deficient, why intrinsic factor is the bottleneck, what the oral-versus-injection trials found, and what happens when you supplement a level that was already normal.
Glutathione — Glutathione is a three-amino-acid molecule your cells synthesise constantly and depend on for redox defense and detoxification. A six-month randomized trial showed oral supplementation can raise body stores. Outcome data for injections is thin, and the skin-lightening marketing outruns the evidence by a wide margin.

Sexual Health

PT-141 — PT-141, bremelanotide, works on melanocortin receptors in the central nervous system. It was developed and trialled for hypoactive sexual desire disorder in premenopausal women, which is the population the evidence describes. Male use is off-label and thinly studied.

Peptide Research

Epitalon — Epitalon is a four-amino-acid peptide modeled on an older pineal gland extract. Its telomerase results come from cell culture, its longevity results come from animals given the extract, and no published human trial has tested the synthetic peptide itself.
KPV — KPV is a three-amino-acid fragment of alpha-MSH with genuinely interesting anti-inflammatory mechanics in cells and mouse models of colitis. The count of large controlled human trials is zero, and that number is the whole story.
MOTS-c — MOTS-c is a peptide encoded not by the nucleus but by mitochondrial DNA. The mouse metabolic data is strong and the human exercise association is real, but no large trial has tested injecting it into people.
Semax — Semax is a synthetic fragment of ACTH developed in Russia and registered as a medicine there. Its neurotrophic findings come from rat ischemia models, its clinical data from Russian stroke patients, and no Western trial in healthy people exists.
TB-500 — TB-500 is marketed as thymosin beta-4, but it is a short fragment of it. The parent protein has small human trials. The fragment has none, and it carries doping-agent status with published detection methods.
Peptide Stacking — Stacking peptides means combining several agents that were each studied alone, if they were studied in humans at all. Ranking the individual evidence bases makes clear how uneven the pile really is, and none of it says anything about what happens when the compounds are taken together.
Peptides After 30 — Growth hormone output does decline with age, and that decline is real and measurable. But the specific statistics that circulate about it, muscle loss per decade, the 1990 GH trial, are mostly misquoted. Here is what the underlying studies actually found.

Skin Science

Copper peptides (GHK-Cu) — GHK-Cu is one of the best-characterised signalling peptides in skin biology and one of the least tested in people. The lab work is real and repeatedly reproduced. The large human trial of an isolated copper peptide does not exist, and several of the numbers circulating online have no traceable source at all.
Copper peptides for hair — The hair claims for copper peptides rest on one 2007 in-vitro follicle study and a first-in-man pilot of a multi-ingredient injectable that cannot credit GHK-Cu alone. No controlled human regrowth trial exists, and nothing has been compared against minoxidil.
How to use copper peptides — Copper peptides are signalling molecules, not exfoliants, so more product does not mean more effect. Consistency matters more than time of day, results are measured in weeks, and the advice to separate them from strong acids is a formulation-chemistry precaution rather than a documented safety problem.
Copper peptides vs retinol — This comparison is not close on the dimension that matters. Retinoids have vehicle-controlled human trials with measured outcomes in photoaged skin. Copper peptides have cell culture, ex-vivo skin, and gene-expression analysis. Retinoids are the evidence pick; copper peptides are a reasonable gentle complement.
NAD+ and skin — NAD+, nicotinamide, and niacinamide get used interchangeably in skincare marketing. They are related but distinct, and the human evidence behind them is not interchangeable at all. One has a genuine phase 3 trial. The others do not.
Skin and the liver — Acne and dullness get blamed on a backed-up liver 'dumping toxins' through the skin. The liver does not excrete through skin, and it has its own specific, recognisable warning signs when something is actually wrong with it. This is what the evidence supports instead.