Fundamentals
Have you found yourself noticing subtle shifts in your body, perhaps a persistent dip in energy that wasn’t there before, or a feeling of diminished vitality that seems to settle in despite your best efforts? Many individuals, as they navigate the passage of years, experience a quiet but undeniable change in their physical and mental landscape.
This often manifests as a reduction in stamina, a less restful sleep, or a subtle alteration in body composition, where maintaining muscle mass becomes more challenging and unwanted weight seems to accumulate with greater ease. These experiences are not simply a consequence of growing older; they frequently signal a deeper, systemic recalibration within the body’s intricate hormonal architecture.
Understanding these internal signals marks the initial step toward reclaiming a sense of well-being. Your body communicates through a sophisticated network of chemical messengers, and when these messages become less clear or less frequent, the impact is felt across various physiological domains.
This section begins a discussion of how these biological systems operate and how specific interventions, such as peptide therapies, offer a pathway to restoring balance and function. We aim to provide a clear, evidence-based explanation of the underlying biological mechanisms, translating complex clinical science into empowering knowledge for your personal journey.
The body’s subtle shifts in energy and composition often indicate deeper hormonal recalibrations.
The Body’s Internal Messaging System
The human body operates through a remarkable system of communication, where specialized glands release chemical messengers known as hormones. These substances travel through the bloodstream, delivering instructions to various cells and tissues, orchestrating nearly every bodily function. From regulating metabolism and mood to influencing sleep patterns and physical strength, hormones act as vital conductors in the symphony of your physiological processes.
As individuals age, the production and regulation of these essential messengers can undergo changes, leading to a cascade of effects that impact overall health and daily experience.
Consider the endocrine system as the body’s central command center for these chemical signals. It comprises glands such as the pituitary, thyroid, adrenal, and gonads, each contributing to a delicate equilibrium. When this balance is disrupted, whether by age, environmental factors, or lifestyle choices, the resulting symptoms can be wide-ranging and often perplexing. A comprehensive understanding of these interconnected systems provides a framework for addressing symptoms not as isolated occurrences, but as indicators of systemic imbalances.
Age Related Hormonal Changes
The natural progression of aging brings about predictable, yet individually varied, alterations in hormonal output. For men, a gradual decline in testosterone production, often termed andropause, can begin as early as the third decade of life. This reduction can lead to symptoms such as decreased libido, reduced muscle mass, increased body fat, fatigue, and mood disturbances.
Similarly, women experience significant hormonal shifts during perimenopause and post-menopause, characterized by fluctuating and eventually declining levels of estrogen and progesterone. These changes can manifest as hot flashes, irregular cycles, sleep disturbances, mood swings, and a reduction in bone density.
Beyond the primary sex hormones, other vital endocrine glands also experience age-related changes. Growth hormone (GH) secretion, for instance, typically diminishes with advancing years, a phenomenon sometimes referred to as somatopause. This reduction in GH can contribute to decreased muscle mass, increased adiposity, reduced bone density, and a general decline in tissue repair capabilities. Addressing these multifaceted hormonal changes requires a nuanced and personalized approach, moving beyond a single-hormone focus to consider the entire endocrine network.
Understanding Hormonal Feedback Loops
Hormonal systems operate on intricate feedback loops, similar to a home thermostat. When a hormone level drops below a certain set point, the body’s regulatory centers, primarily the hypothalamus and pituitary gland in the brain, signal the relevant endocrine gland to increase production. Conversely, when levels rise too high, a negative feedback mechanism signals a reduction in production. This constant adjustment maintains physiological stability.
The Hypothalamic-Pituitary-Gonadal (HPG) axis exemplifies this complex interplay. The hypothalamus releases gonadotropin-releasing hormone (GnRH), which prompts the pituitary gland to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These gonadotropins then act on the gonads (testes in men, ovaries in women) to stimulate the production of sex hormones like testosterone, estrogen, and progesterone. As we age, various points along this axis can become less responsive or less efficient, contributing to the observed hormonal declines.
Peptide therapies offer a sophisticated way to interact with these feedback loops, often by stimulating the body’s own natural production mechanisms rather than simply replacing hormones from an external source. This approach aims to recalibrate the system, encouraging the body to restore its inherent functional capacity.
Intermediate
Having established the foundational understanding of hormonal systems and age-related changes, we now consider specific clinical protocols designed to restore balance and vitality. Peptide therapies, alongside targeted hormonal optimization protocols, represent a cutting-edge approach to addressing the complex interplay of the endocrine system. These interventions are not about merely masking symptoms; they are about supporting the body’s intrinsic ability to regulate and regenerate, providing a more physiological pathway to well-being.
The precision of these protocols allows for highly individualized treatment plans, recognizing that each person’s biological landscape is unique. We will explore the ‘how’ and ‘why’ behind these therapies, detailing specific agents and their mechanisms of action, always with an emphasis on translating scientific principles into practical, empowering knowledge.
Peptide therapies and hormonal optimization protocols support the body’s intrinsic ability to regulate and regenerate.
Targeted Hormonal Optimization Protocols
Hormonal optimization protocols are designed to address specific deficiencies or imbalances identified through comprehensive laboratory analysis and clinical evaluation. These protocols often involve the administration of bioidentical hormones, which are chemically identical to those naturally produced by the body, ensuring a more harmonious integration with existing biological pathways. The goal is to restore hormone levels to a youthful, optimal range, thereby alleviating symptoms and promoting overall health.
Testosterone Replacement Therapy Men
For men experiencing symptoms of low testosterone, a condition often referred to as hypogonadism or andropause, Testosterone Replacement Therapy (TRT) can significantly improve quality of life. A standard protocol often involves weekly intramuscular injections of Testosterone Cypionate, typically at a concentration of 200mg/ml. This method provides a steady release of testosterone into the bloodstream, helping to normalize levels and alleviate symptoms such as fatigue, reduced muscle mass, increased body fat, and diminished libido.
To maintain the body’s natural testicular function and preserve fertility, Gonadorelin is frequently co-administered. This peptide, a synthetic analog of GnRH, stimulates the pituitary gland to release LH and FSH, thereby encouraging the testes to continue their own testosterone production and spermatogenesis. Gonadorelin is typically administered via subcutaneous injections, twice weekly.
Additionally, managing the conversion of testosterone to estrogen is a critical aspect of male hormonal optimization. Testosterone can be converted into estrogen by the enzyme aromatase. Elevated estrogen levels in men can lead to side effects such as gynecomastia (breast tissue development) and water retention.
To mitigate this, an aromatase inhibitor like Anastrozole is often prescribed, typically as an oral tablet taken twice weekly. This medication helps to block the aromatase enzyme, maintaining a healthy testosterone-to-estrogen ratio. In some cases, Enclomiphene may be included to further support LH and FSH levels, particularly when fertility preservation is a primary concern.
How Does Anastrozole Influence Estrogen Levels In Men?
Testosterone Replacement Therapy Women
Women, too, can experience the benefits of testosterone optimization, particularly those in pre-menopausal, peri-menopausal, or post-menopausal stages who present with symptoms such as irregular cycles, mood changes, hot flashes, or reduced libido. While testosterone levels in women are naturally much lower than in men, even a subtle deficiency can significantly impact well-being.
Protocols for women often involve lower doses of Testosterone Cypionate, typically 10 ∞ 20 units (0.1 ∞ 0.2ml) weekly via subcutaneous injection. This precise dosing aims to restore testosterone to physiological female ranges, supporting energy, mood, and sexual health without inducing androgenic side effects. Progesterone is prescribed based on menopausal status, playing a vital role in uterine health for women with an intact uterus and contributing to mood stability and sleep quality for all women.
Another delivery method gaining recognition is pellet therapy. Small, bioidentical testosterone pellets, approximately the size of a grain of rice, are inserted subcutaneously, usually in the hip area. These pellets provide a consistent, sustained release of testosterone over several months, avoiding daily injections or topical applications. When appropriate, Anastrozole may also be used in women to manage estrogen conversion, particularly in cases where testosterone is being used to address menopausal symptoms and estrogen levels need careful modulation.
| Method | Administration Frequency | Advantages | Considerations |
|---|---|---|---|
| Subcutaneous Injection | Weekly | Precise dosing, consistent levels, patient self-administration | Requires regular injections, potential for local site reactions |
| Pellet Therapy | Every 3-5 months | Sustained release, convenience, avoids daily application | Minor surgical procedure for insertion, less flexible dosing adjustments |
Post TRT or Fertility Stimulating Protocol Men
For men who have discontinued TRT or are actively trying to conceive, a specialized protocol is employed to reactivate the body’s natural testosterone production and support spermatogenesis. This protocol typically includes a combination of medications designed to stimulate the HPG axis.
- Gonadorelin ∞ Administered to stimulate the pituitary gland, prompting the release of LH and FSH, which are essential for testicular function and sperm production.
- Tamoxifen ∞ A selective estrogen receptor modulator (SERM) that blocks estrogen’s negative feedback on the hypothalamus and pituitary, leading to increased LH and FSH secretion and, consequently, higher endogenous testosterone production.
- Clomid (Clomiphene Citrate) ∞ Another SERM that works similarly to Tamoxifen, stimulating gonadotropin release and testicular function. It is widely used to restore fertility in men with hypogonadism.
- Anastrozole ∞ Optionally included to manage estrogen levels, particularly if there is a concern about excessive estrogen conversion during the process of stimulating endogenous testosterone production.
This carefully orchestrated protocol aims to restore the body’s own hormonal rhythm, allowing for a return to natural function and reproductive capacity.
Growth Hormone Peptide Therapy
Beyond traditional hormone replacement, peptide therapies offer a distinct and powerful avenue for optimizing health, particularly in active adults and athletes seeking anti-aging benefits, muscle gain, fat loss, and improved sleep. These peptides work by stimulating the body’s own production of growth hormone, rather than introducing exogenous GH, leading to a more physiological release pattern and often fewer side effects.
Key peptides in this category include:
- Sermorelin ∞ A growth hormone-releasing hormone (GHRH) analog that stimulates the pituitary gland to secrete natural growth hormone. It mimics the body’s own GHRH, leading to increased GH and IGF-1 levels, supporting muscle mass and reducing body fat.
- Ipamorelin / CJC-1295 ∞ Often used in combination due to their synergistic effects. Ipamorelin is a selective growth hormone secretagogue (GHRP) that binds to ghrelin receptors, inducing GH release without significantly affecting cortisol or prolactin levels. CJC-1295 is a modified GHRH analog. When combined with DAC (Drug Affinity Complex), it provides a sustained release of GH over approximately one week, while the non-DAC form (Modified GRF 1-29) offers a shorter, more pulsatile release. This combination promotes muscle growth, fat loss, and improved recovery.
- Tesamorelin ∞ A GHRH analog specifically approved for reducing visceral adipose tissue in certain conditions. It has shown promise in improving body composition and metabolic markers.
- Hexarelin ∞ Another GHRP that stimulates GH release, often noted for its potential cardiovascular benefits and effects on tissue repair.
- MK-677 (Ibutamoren) ∞ A non-peptide growth hormone secretagogue that stimulates GH release by mimicking ghrelin. It is orally active and provides a sustained increase in GH and IGF-1 levels, supporting muscle gain, fat loss, and sleep quality.
These peptides represent a sophisticated approach to enhancing the body’s regenerative capabilities, supporting metabolic efficiency, and promoting a more youthful physiological state.
What Distinguishes Sermorelin From CJC-1295 In Growth Hormone Stimulation?
Other Targeted Peptides
Beyond growth hormone optimization, other peptides offer highly specific therapeutic benefits, addressing a range of concerns from sexual health to tissue repair and inflammation. These compounds exemplify the precision of peptide science, targeting specific cellular functions and signaling pathways to restore balance and promote healing.
- PT-141 (Bremelanotide) for sexual health ∞ This peptide acts on the central nervous system, specifically activating melanocortin receptors in the brain. Unlike traditional medications that primarily affect blood flow, PT-141 directly influences sexual desire and arousal in both men and women. It is a valuable option for individuals whose sexual dysfunction has a neuropsychological or hormonal component, rather than solely vascular issues.
- Pentadeca Arginate (PDA) for tissue repair, healing, and inflammation ∞ PDA is a synthetic peptide derived from BPC-157, a naturally occurring peptide found in human gastric juice. It is recognized for its remarkable regenerative and anti-inflammatory properties. PDA supports accelerated healing of various tissues, including muscles, tendons, ligaments, and skin. It promotes collagen synthesis, reduces pain, and mitigates inflammatory responses, making it beneficial for injury recovery, chronic pain, and even gut health.
These specialized peptides highlight the versatility of peptide therapies in addressing specific health challenges, offering targeted solutions that work in harmony with the body’s natural healing and regulatory mechanisms.
Academic
The exploration of peptide therapies and hormonal balance in aging individuals necessitates a deep dive into the underlying endocrinology and systems biology. This section elevates the discussion to an academic level, analyzing the intricate mechanisms by which these compounds interact with the body’s complex regulatory networks.
We will examine clinical evidence, molecular pathways, and the interconnectedness of various biological axes, maintaining the “Clinical Translator” voice to ensure even the most sophisticated concepts remain clear and relevant to the ultimate goal of patient well-being.
The human endocrine system is not a collection of isolated glands; it functions as a highly integrated orchestra, where each hormone and peptide plays a specific role, influencing and being influenced by others. Understanding this symphony is paramount to designing effective, personalized wellness protocols that truly restore vitality.
The endocrine system operates as an integrated orchestra, where each hormone and peptide influences others.
The Hypothalamic Pituitary Axis and Aging
The central control of hormonal regulation resides within the hypothalamic-pituitary axis, a critical neuroendocrine interface. This axis, comprising the hypothalamus in the brain and the pituitary gland, orchestrates the release of various trophic hormones that, in turn, stimulate peripheral endocrine glands. With advancing age, subtle yet significant adaptations occur within this axis, contributing to the observed declines in circulating hormone levels.
In the context of the Hypothalamic-Pituitary-Gonadal (HPG) axis, aging is associated with changes at multiple levels. Research indicates a diminished pulsatile secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus in older men, leading to reduced stimulation of the pituitary gland.
This hypothalamic adaptation contributes to the decline in luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are essential for testicular testosterone production. While the pituitary’s responsiveness to exogenous GnRH may remain largely intact, the reduced upstream signaling from the hypothalamus is a primary driver of age-related hypogonadism.
Similarly, the Hypothalamic-Pituitary-Somatotropic (HPS) axis, responsible for growth hormone (GH) regulation, also undergoes age-related changes. The pulsatile release of growth hormone-releasing hormone (GHRH) from the hypothalamus decreases with age, leading to a reduction in GH secretion from the pituitary.
This decline in GH, often termed somatopause, results in lower levels of insulin-like growth factor 1 (IGF-1), a key mediator of GH’s anabolic effects. The consequences include reduced muscle mass (sarcopenia), increased visceral adiposity, and diminished tissue repair capacity.
Peptide therapies like Sermorelin and CJC-1295 directly address these age-related changes in the HPS axis by acting as GHRH analogs, stimulating the pituitary to release GH in a more physiological, pulsatile manner. This approach leverages the body’s own regulatory mechanisms, aiming to restore the natural rhythm of GH secretion rather than simply flooding the system with exogenous hormone.
The Interplay of Hormones and Metabolic Function
Hormonal balance is inextricably linked to metabolic function. Hormones such as insulin, thyroid hormones, cortisol, and sex hormones collectively regulate energy expenditure, nutrient utilization, and body composition. Age-related hormonal shifts can disrupt this delicate metabolic equilibrium, contributing to insulin resistance, altered fat distribution, and reduced metabolic rate.
For instance, declining testosterone levels in men are associated with increased insulin resistance and a higher prevalence of metabolic syndrome. In women, the hormonal changes of menopause can lead to a redistribution of fat towards the abdominal area and an increased risk of cardiovascular disease. Growth hormone deficiency also contributes to adverse body composition changes and metabolic dysregulation.
Peptide therapies and hormonal optimization protocols, by restoring hormonal balance, can exert profound positive effects on metabolic health. By optimizing testosterone, for example, men may experience improved insulin sensitivity and a more favorable body composition. Similarly, supporting GH levels with peptides can enhance fat metabolism and muscle protein synthesis, contributing to a healthier metabolic profile.
This systems-biology perspective underscores that addressing hormonal imbalances is not merely about alleviating symptoms, but about recalibrating fundamental physiological processes that underpin overall health and longevity.
Advanced Peptide Mechanisms and Clinical Applications
The therapeutic utility of peptides lies in their highly specific interactions with cellular receptors and signaling pathways. Unlike larger proteins, their smaller size allows for more efficient cellular penetration and targeted action.
Growth Hormone Releasing Peptides Molecular Action
Sermorelin, a 29-amino acid peptide, is a synthetic analog of the naturally occurring GHRH. It binds to specific GHRH receptors on somatotroph cells in the anterior pituitary gland, stimulating the synthesis and pulsatile release of endogenous growth hormone. This mechanism avoids the potential negative feedback associated with exogenous GH administration, allowing the body’s natural regulatory systems to remain engaged.
CJC-1295, particularly the version with Drug Affinity Complex (DAC), is a modified GHRH analog designed for a prolonged half-life. The DAC component allows CJC-1295 to bind reversibly to serum albumin, extending its activity and providing a sustained release of GHRH, which in turn leads to a more consistent elevation of GH and IGF-1 levels over several days. This sustained action makes it a practical option for less frequent dosing.
Ipamorelin, a selective growth hormone secretagogue (GHRP), acts on ghrelin receptors in the pituitary and hypothalamus. It stimulates GH release without significantly increasing levels of cortisol, prolactin, or adrenocorticotropic hormone (ACTH), which can be undesirable side effects with some other GHRPs. This selectivity makes Ipamorelin a preferred choice for a cleaner GH release profile, often combined with CJC-1295 to maximize both pulsatile and sustained GH stimulation.
The combined administration of CJC-1295 and Ipamorelin leverages their complementary mechanisms ∞ CJC-1295 provides a sustained GHRH signal, while Ipamorelin offers a pulsatile GH release, mimicking the body’s natural rhythm more closely. This synergy results in enhanced muscle protein synthesis, lipolysis (fat breakdown), and improved recovery processes.
| Peptide | Primary Mechanism | Key Benefits |
|---|---|---|
| Sermorelin | GHRH analog, stimulates pituitary GHRH receptors | Natural GH release, muscle gain, fat reduction, improved sleep |
| CJC-1295 (with DAC) | Long-acting GHRH analog, binds to albumin for sustained release | Consistent GH/IGF-1 elevation, enhanced recovery, anti-aging effects |
| Ipamorelin | Selective GHRP, acts on ghrelin receptors | Pulsatile GH release, minimal side effects, muscle tone, fat loss |
| MK-677 | Oral GH secretagogue, mimics ghrelin | Sustained GH/IGF-1 increase, muscle gain, improved sleep |
PT-141 Neurobiological Pathways
PT-141 (Bremelanotide) operates through a distinct neurobiological pathway, differentiating it from vascular-acting erectile dysfunction medications. It is a synthetic analog of alpha-melanocyte-stimulating hormone (α-MSH) and acts as an agonist at melanocortin receptors, specifically MC3R and MC4R, located in the central nervous system. These receptors are highly concentrated in areas of the brain associated with sexual function, including the hypothalamus and the medial preoptic area.
Activation of MC4 receptors by PT-141 is thought to increase the release of dopamine in these brain regions. Dopamine, a neurotransmitter, plays a critical role in reward, motivation, and sexual arousal. By modulating these central pathways, PT-141 directly stimulates sexual desire and arousal, initiating the physiological cascade that leads to sexual response in both men and women.
This central action makes it particularly effective for individuals with psychogenic or neurologically mediated sexual dysfunction, where traditional blood flow-enhancing agents may be insufficient.
Can Peptide Therapies Address Sexual Dysfunction Beyond Blood Flow Issues?
Pentadeca Arginate Cellular Mechanisms
Pentadeca Arginate (PDA), a synthetic derivative of BPC-157, exerts its therapeutic effects through a multifaceted cellular mechanism, primarily centered on tissue repair, angiogenesis, and anti-inflammatory actions. PDA retains the 15-amino acid sequence of BPC-157, enhanced with an arginate salt for improved stability and bioavailability.
Research indicates that PDA promotes the survival of cells under stress and accelerates the healing of various tissues, including tendons, ligaments, muscles, and gastrointestinal mucosa. Its actions include:
- Angiogenesis ∞ PDA stimulates the formation of new blood vessels, which is critical for delivering oxygen and nutrients to injured tissues, thereby accelerating the healing process.
- Collagen Synthesis ∞ It enhances the production of type I collagen, a primary structural protein in connective tissues, leading to stronger and more resilient tissue repair.
- Fibroblast Migration and Proliferation ∞ PDA promotes the migration and proliferation of fibroblasts, cells essential for wound healing and tissue remodeling.
- Anti-inflammatory Effects ∞ It modulates inflammatory mediators, reducing pain and swelling in injured areas. This anti-inflammatory action is crucial for preventing chronic inflammation, which can impede healing.
- Growth Factor Expression ∞ PDA has been shown to influence the expression of various growth factors, including growth hormone receptors in tendon fibroblasts, further supporting tissue regeneration.
These mechanisms collectively contribute to PDA’s remarkable ability to accelerate recovery from injuries, reduce chronic pain, and support the integrity of various organ systems, including the gastrointestinal tract. Its broad regenerative potential positions it as a valuable tool in advanced wellness protocols.
References
- Veldhuis, J. D. et al. (2006). Aging and hormones of the hypothalamo-pituitary axis ∞ gonadotropic axis in men and somatotropic axes in men and women. Journal of Clinical Endocrinology & Metabolism, 91(3), 799-805.
- Veldhuis, J. D. et al. (2007). The Aging Male Hypothalamic-Pituitary-Gonadal Axis ∞ pulsatility and feedback. Journal of Clinical Endocrinology & Metabolism, 92(12), 4792-4797.
- Ionescu, M. & Frohman, L. A. (2006). Pulsatile secretion of growth hormone (GH) persists during continuous stimulation by CJC-1295, a long-acting GH-releasing hormone analog. Journal of Clinical Endocrinology & Metabolism, 91(12), 4792-4797.
- Teichman, S. L. et al. (2005). Prolonged stimulation of growth hormone (GH) and insulin-like growth factor I secretion by CJC-1295, a long-acting analog of GH-releasing hormone, in healthy adults. Journal of Clinical Endocrinology and Metabolism, 91(3), 799-805.
- Hamoda, H. et al. (2020). The British Menopause Society & Women’s Health Concern 2020 recommendations on hormone replacement therapy in menopausal women. Post Reproductive Health, 26(4), 181-209.
- Islam, R. M. et al. (2019). Safety and efficacy of testosterone for women ∞ a systematic review and meta-analysis of randomised controlled trial data. Lancet Diabetes & Endocrinology, 7(10), 754-764.
- Vukojević, J. et al. (2018). Body protection compound 157 and its effects on the central nervous system. Current Medicinal Chemistry, 25(16), 1883-1891.
- Sikirić, P. C. et al. (2010). A new gastric pentadecapeptide, BPC 157, is an antiulcer peptide with a therapeutic potential in various conditions. Journal of Physiology and Pharmacology, 61(2), 171-180.
- Pfaus, J. G. et al. (2008). The melanocortin system and sexual function. Pharmacology Biochemistry and Behavior, 90(2), 163-172.
- Diamond, L. E. et al. (2004). The effect of subcutaneous administration of bremelanotide on erectile dysfunction ∞ a multicenter, randomized, placebo-controlled trial. Journal of Urology, 172(2), 642-645.
Reflection
As we conclude this exploration of hormonal health and peptide therapies, consider the knowledge gained not as a final destination, but as a compass for your ongoing health journey. The intricate biological systems within you are constantly adapting, and understanding their language is a powerful act of self-care. The symptoms you experience are not merely inconveniences; they are valuable signals from your body, inviting a deeper inquiry into its needs.
This discussion has aimed to translate complex scientific principles into actionable insights, providing a framework for understanding how personalized wellness protocols can support your unique physiology. The path to reclaiming vitality and optimal function is deeply personal, requiring a partnership with knowledgeable clinical guidance that respects your lived experience while applying evidence-based strategies.
May this information serve as a catalyst for your continued introspection, empowering you to pursue a future where your biological systems operate with renewed vigor and harmony.
Glossary
body composition
muscle mass
peptide therapies
endocrine system
testosterone production
reduced muscle mass
perimenopause
age-related changes
growth hormone
pituitary gland
peptide therapies offer
targeted hormonal optimization protocols
clinical protocols
hormonal optimization protocols
bioidentical hormones
testosterone replacement therapy
testosterone cypionate
gonadorelin
hormonal optimization
estrogen levels
anastrozole
side effects
sustained release
muscle gain
fat loss
selective growth hormone secretagogue
pulsatile release
ghrh analog
tissue repair
growth hormone secretagogue
central nervous system
melanocortin receptors
