Peptides and Hormones for Fatigue? Evidence, Risks & What to Ask First

Peptides, hormone testing, adaptogens, and senolytics are often marketed as shortcuts for fatigue and “energy optimization.” In this episode, Dr. Hillary…

Published October 28, 2024The Longevity Show

Up to 15% of adults report feeling tired every single day for the past three months — not occasionally, every day, regardless of how much they sleep. Dr. Lin's framing is that for most people there will be an identifiable cause, but a real subset have optimised sleep, nutrition and stress management and remain exhausted. This episode is for that subset, and she is upfront that many listeners will not need these tools now but should know they exist for when they do.

The organising idea is that peptides are messages rather than materials. Where a protein is a large machine of hundreds or thousands of amino acids, a peptide is typically 2 to 50 — small enough to be absorbed readily and act fast, and specific enough to instruct one process precisely. Dr. Lin's point is that people already use them without realising: collagen peptides, creatine, and the GLP-1 agonists now taken by an enormous number of people are all peptide-based, working by mimicking a naturally occurring hormone at concentrations the body could never produce itself.

The second half covers the endocrine systems that determine whether energy is available at all — thyroid, cortisol, and DHEA and testosterone. This is where her caution sharpens. Much of the peptide evidence is preclinical rather than human, several are on the World Anti-Doping Agency banned list, and she is explicit about not buying them from grey or black markets. On hormones her warning is different in kind: she notes that the majority of physicians are not trained in this area and may hold outdated views, so finding someone experienced matters more than usual.

Before you watch

Peptides work as signalling molecules rather than raw building blocks, and that distinction explains their appeal. A peptide of 2 to 50 amino acids is small enough to be absorbed without the usual digestion large proteins require, and specific enough to instruct one process — Dr. Lin's comparison is that if proteins are complex machines running several functions at once, peptides are specialised tools designed for a single task with precision.
You are probably already taking peptides. Collagen peptides are fragments of larger collagen proteins. Creatine supports both muscle output and brain function, which Dr. Lin highlights as particularly useful during periods of stress — jet lag, night shifts, sleep disrupted by children or pets — and notes creatine monohydrate is inexpensive. GLP-1 agonists including semaglutide are peptide-based drugs mimicking a hormone your body already makes, at concentrations far above anything it could produce, which is why they suppress appetite and regulate blood sugar so effectively.
BPC-157 has the most enthusiasm and the least human data. A 15-amino-acid peptide derived from gastric juice, it has shown in preclinical animal studies that it accelerates healing in muscle, tendon and ligament injuries, promotes angiogenesis — the formation of new blood vessels needed for repair — and enhances growth hormone receptor expression, potentially amplifying growth hormone's effects. Dr. Lin is explicit that clinical evidence in humans remains limited, and that the enthusiasm on social media outpaces the trials.
The growth hormone secretagogues work as a pair for a reason. CJC-1295 increases growth hormone release and has been shown to raise both GH and IGF-1, which matter for muscle repair, fat metabolism and recovery. Ipamorelin regulates that release more smoothly, preventing the spikes and crashes associated with other secretagogues. Dr. Lin notes direct evidence linking these to mitochondrial function is limited — the energy benefit is indirect, through improved recovery and lean muscle.
Two mitochondrial peptides are worth knowing but remain preclinical. MOTS-c helps regulate metabolism and increases insulin sensitivity, improving energy efficiency at the cellular level. Humanin protects cells from oxidative stress and supports mitochondrial function. Both show promise for delaying age-related declines in energy production, and both are still at the animal stage. She also flags epitalon for telomere maintenance and thymosin alpha-1 for immune function as topics deserving their own episode.
The peptide safety guidance is unusually firm for this show. They are not a substitute for foundational habits. Medical supervision is essential given that dosing, safety and monitoring all matter and side effects exist. Many peptides appear on the World Anti-Doping Agency banned list, so competitive athletes need to check before using anything. And her clearest instruction: do not buy peptides from the grey or black market — this needs to be done properly and under a physician's supervision.
Thyroid dysfunction can present as depression, which is why she argues it belongs in any mental health workup. T3 and T4 control how quickly cells convert nutrients into energy, so even mild hypothyroidism slows metabolism and produces fatigue, mental fog, weight gain and cold intolerance — a state some people describe as depression, meaning thyroid should be checked during evaluation rather than after treatment fails. The related trap is subclinical hypothyroidism, where results sit inside the reference range while energy and wellbeing remain low; Dr. Lin's approach is to work toward the TSH, T3 and T4 levels that function for that individual rather than treating the population range as the target, with levothyroxine as the mainstay and T3 added for those who do not fully respond to T4 alone.
Her thyroid nutrition guidance comes with specific cautions on two minerals. Iodine is essential for thyroid hormone synthesis — available from seaweed, dairy and eggs, and she notes natural salts lack the iodine that table salt is fortified with, alongside a population study finding higher seaweed consumption associated with lower thyroid cancer prevalence. Selenium converts T4 into active T3, from Brazil nuts, seafood and organ meats, all of which can be overdone. Zinc she recommends getting from food rather than supplements, because excess blocks absorption of other micronutrients. And iron is genuinely person-dependent — most people do not need more, but menstruating women may, and low iron is an often-missed cause of restless legs syndrome alongside fatigue.
Cortisol dysregulation runs in both directions, and the direction changes the presentation. Chronically elevated cortisol produces energy crashes, poor sleep, weight gain concentrated as visceral fat, and difficulty recovering from exertion — and Dr. Lin flags early morning awakening, several hours before you intend to wake, as a specific signal. Chronically low cortisol from prolonged stress produces extreme fatigue, poor recovery from illness and reduced capacity to handle stress. Her caveat matters: the goal is not simply lower cortisol, since without the morning rise you would have no drive to get up at all.
The adaptogen evidence is better than the category's reputation suggests. A systematic review last year found ashwagandha consistently reduced cortisol secretion in stressed individuals without major adverse effects, while also improving overall stress resilience. Rhodiola rosea modulates the HPA axis, reducing cortisol and improving mental performance and fatigue in highly stressed people. Siberian ginseng and Schisandra chinensis have both been shown to improve stress resistance and normalise cortisol secretion. On testing, she recommends going beyond a single morning blood cortisol to salivary testing, which captures the pattern across the day and around specific activities.
Birth control pills are not hormone replacement therapy, and Dr. Lin is direct about the confusion. Oral contraceptives use synthetic hormones rather than the body-identical ones used in HRT, and at levels far too low to restore energy or deliver HRT's other benefits. Her more interesting observation is what that proves: if the very small hormone doses in a contraceptive pill can noticeably alter mood, the system is sensitive enough that genuine imbalances are worth measuring and correcting. She adds that most physicians are not trained in this area and may carry outdated views on hormone therapy, so experience matters when choosing who to work with.

Chapters

Questions

What are peptides and how are they different from protein?

Peptides are short chains of amino acids, typically between 2 and 50, while proteins are much larger structures of hundreds or thousands. That size difference matters practically: smaller peptides are absorbed more easily and act faster, without needing the full digestion a large protein requires. More importantly, they function as signalling molecules — Dr. Lin describes them as text messages telling specific cells what to do, whether that is repairing tissue, increasing hormone production or reducing inflammation. Her framing is that if proteins are complex machines performing several functions simultaneously, peptides are specialised tools designed to complete one task precisely, which is what makes them so targetable.

Does BPC-157 actually work?

The mechanism is interesting and the human evidence is thin, which is the honest summary. BPC-157 is a 15-amino-acid peptide derived from gastric juice, and preclinical animal studies show it accelerates healing in muscle, tendon and ligament injuries, promotes angiogenesis — the formation of new blood vessels essential to tissue repair — and enhances growth hormone receptor expression, which could amplify growth hormone's healing effects. Dr. Lin is explicit that most of this research is non-human and that clinical evidence remains limited. Her accompanying cautions are that it requires medical supervision, that many peptides appear on the World Anti-Doping Agency banned list, and that buying from grey or black market sources is not acceptable.

Could my fatigue be thyroid-related even if my labs are normal?

Yes, and Dr. Lin describes this as subclinical hypothyroidism — results falling within the reference range while symptoms like low energy and a diminished sense of wellbeing persist. Her approach is to identify the TSH, T3 and T4 levels that work for that specific person rather than treating the population range as the target, which is an area she says requires working closely with patients rather than applying a standard. She also makes a related point worth acting on: because mild hypothyroidism can present as depression, thyroid function belongs in the workup for anyone being evaluated for depression or anxiety, not as an afterthought once treatment has failed.

What does high cortisol feel like?

Chronically elevated cortisol tends to produce energy crashes, poor sleep, weight gain concentrated around the middle as visceral fat, and difficulty recovering from physical activity. Dr. Lin highlights one specific and often overlooked signal: waking several hours earlier than you intend to, feeling you have not had enough sleep, which can reflect elevated cortisol. The complication is that dysregulation runs both ways — chronically low cortisol from prolonged stress produces extreme fatigue, poor recovery from illness and reduced ability to handle stress at all. Her caveat is that the aim is not simply to lower cortisol, since the morning rise is what gets you out of bed.

Do adaptogens like ashwagandha actually lower cortisol?

The evidence is stronger than the category's reputation. A systematic review published last year found ashwagandha supplementation consistently reduced cortisol secretion in stressed individuals, notably without major adverse effects, making it viable for longer-term use — and the trials showed improved overall stress resilience alongside the cortisol reduction. Rhodiola rosea modulates the HPA axis, the pathway controlling cortisol production, with studies showing reduced cortisol and improved mental performance and fatigue in highly stressed people. Siberian ginseng and Schisandra chinensis are both recognised for improving stress resistance and normalising cortisol secretion. Dr. Lin pairs these with antioxidants, preferably from food, to address the oxidative stress accompanying cortisol dysregulation.

Is my birth control pill enough hormone support?

No, and Dr. Lin is unambiguous about it. Oral contraceptives use synthetic hormones rather than the body-identical or bioidentical forms used in hormone replacement therapy, and the doses are low — designed to regulate cycles rather than restore physiological levels. They will not deliver the energy or other benefits associated with HRT. What she finds instructive is the implication: if the small amounts in a contraceptive pill can produce significant mood effects, the system is sensitive enough that measuring and correcting genuine imbalances is worthwhile. She adds a practical warning that the majority of doctors are not trained in hormone therapy and may hold outdated ideas, so finding an experienced clinician matters.

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