Sermorelin + Thymosin Alpha-1 Stack: Safety and Monitoring Guide

What does sermorelin do, and what did its trials measure?

Sermorelin is a 29-amino-acid analogue of human growth hormone-releasing hormone, the shortest synthetic peptide with the full biological activity of GHRH. It is not growth hormone itself [8]. It acts on the pituitary's GHRH receptor to make the body release its own growth hormone, and its effect is short-lived. In a study of 30 healthy men given GHRH(1-29)-NH2 intravenously or intranasally, the peptide was rapidly eliminated after intravenous injection while growth hormone stayed raised for about three hours [9].

Sermorelin acetate was FDA-approved as Geref, first as a 0.05 mg/ampule diagnostic product in 1990 and then as 0.5 mg and 1 mg vials for treating idiopathic growth hormone deficiency in children in 1997 [3]. The maker discontinued Geref in 2008 and asked FDA to withdraw the applications; FDA withdrew both approvals effective June 18, 2009, and in March 2013 determined it was not withdrawn from sale for reasons of safety or effectiveness [3]. No sermorelin product is FDA-approved today, so there is no current approved dose. US sermorelin supply, including sermorelin, is compounded [3][10].

For context, the doses that were studied: 30 micrograms per kg subcutaneously once daily at bedtime in the pediatric program [1], and 0.5 mg or 1 mg subcutaneously twice daily for 14 days in a study of older men [11]. Those are study doses, not current recommendations.

The pediatric trial enrolled 110 previously untreated prepubertal children with growth hormone deficiency, 86 of whom were evaluable, and treated them for up to one year. Mean height velocity rose from 4.1 cm/yr at baseline to 8.0 cm/yr at 6 months and 7.2 cm/yr at 12 months, and 74% were considered good responders at 6 months. No adverse changes appeared in general biochemical or hormonal analyses, fasting glucose did not change, IGF-I was not excessively generated, and the peptide was well tolerated [1].

The older-men study gave 10 healthy men (mean age 68) 0.5 mg and 1 mg twice daily for 14 days each, and compared them with 9 young men (mean age 26). At the higher dose, 24-hour growth hormone and IGF-I rose to levels not significantly different from the young men [11]. It was a short physiology study, not a clinical-benefit trial.

What does thymosin alpha-1 do, and what does its safety record show?

Thymosin alpha-1 (thymalfasin) is a 28-amino-acid peptide with an acetylated N-terminal end, originally isolated from thymosin fraction 5; thymalfasin is the synthetic version with the same sequence [4]. Zadaxin is the brand of the finished injection sold outside the US at 1.6 mg per vial, and it is not interchangeable with bulk Ta1 powder [4]. After subcutaneous injection it peaks at about 0.7 to 2 hours, clears with a half-life of about 1.8 to 2.6 hours, and showed no accumulation after five days of daily dosing [4]. It is described as an immune modulator that augments T-cell function [12].

It is not FDA-approved. FDA's December 2024 review notes four US orphan drug designations, but orphan designation is a separate process and is not an approval [4]. FDA lists national authorisations in Italy, where Zadaxin is authorised as an adjuvant to influenza vaccination in immunocompromised people, in India for chronic hepatitis B in adults with compensated liver disease and virus replication, and in Hong Kong [4]. Two older reviews whose authors are tied to the Zadaxin developer say it is approved in over 35 countries (2009) or more than 30 countries (2007) [13][14].

The safety record is mixed in quality. FDA searched its adverse-event database on April 22, 2024 and found zero reports for Ta1 [4]. Authors tied to the manufacturer report more than 4,400 people enrolled in trials and over 17 million Zadaxin doses given after marketing, with adverse experiences described as infrequent and mild; that is company-linked data [4]. The stronger independent check is a 2026 Cochrane review of 10 randomised trials in 1,349 adults with chronic hepatitis B, published between 1991 and 2018. There, Ta1 may have caused fewer serious adverse events than comparison treatments (risk ratio 0.72, 95% CI 0.53 to 0.99; 5 trials, 1,056 people; low-certainty evidence) and fewer non-serious events (risk ratio 0.47, 95% CI 0.27 to 0.83; very low-certainty evidence) [15]. Those were hepatitis B patients, not healthy adults taking it for other reasons.

On the autoimmune question, a 2006 study found that Ta1 induced the enzyme IDO in mouse dendritic cells and generated regulatory T cells, which the authors described as a regulatory environment balancing inflammation and tolerance [16]. That is a laboratory mechanism finding, not evidence about people with autoimmune disease.

What do regulators and the Ta1 label say to watch for?

FDA's page on bulk substances that may present significant safety risks still carries its concerns about thymosin alpha-1: significant risk of immunogenicity for certain routes of administration, peptide-impurity and characterisation problems, and safety information inadequate for the agency to understand the extent of any safety issues. The peptide now sits in that page's nominated-but-withdrawn table; it had been in category 2 and came off because the nominators withdrew, not because FDA resolved its concerns [2].

On December 4, 2024, FDA's Pharmacy Compounding Advisory Committee voted 4 yes and 17 no, with no abstentions, on both Ta1 free base and Ta1 acetate; members who voted no cited no compelling evidence of clinical effectiveness and safety [17]. Ta1 appears in none of the three categories on FDA's list for state-licensed pharmacies and physicians [18], and it is in category 3, nominated without adequate support, on FDA's list for outsourcing facilities [19]. It is not one of the six peptides in HHS's October 2026 draft enforcement-discretion policy [20].

As described in FDA's review, Italy's Zadaxin label covers the finished 1.6 mg injection sold outside the US, not a compounded vial. The label gives 1.6 mg subcutaneously or intramuscularly twice weekly for 4 weeks starting at the first vaccination, repeated from week 8 to week 12. It says not for children, contraindicated in pregnancy and breastfeeding, and advises caution in people with allergies or autoimmune disease and caution with other immune-modulating drugs [4].

Sermorelin is not listed on FDA's significant-safety-risk page [2]. On the outsourcing-facility list it is in category 1, under evaluation, marked as a component of FDA-approved drugs [19]; it appears in no category on the state-licensed pharmacy list [18] and is not among the six peptides in the HHS draft policy [20]. With Geref withdrawn, sermorelin sold in the US is compounded, and compounded drugs are not FDA-approved: FDA does not review their safety, effectiveness or quality before they are marketed [10].

What monitoring did the trials actually use?

These are the tests the trials ran, not a recommended protocol for using the two peptides together. The one-year sermorelin pediatric trial tracked general biochemistry and hormonal panels, fasting glucose and IGF-I, with measures monitored every 3 to 6 months [1]. The 1992 study in older men measured 24-hour growth hormone profiles and IGF-I [11].

On the thymosin alpha-1 side, a 2012 pilot that added Zadaxin to a pandemic H1N1 influenza vaccine in haemodialysed patients assessed safety by adverse-event recording, haematology and chemistry laboratory assays, electrocardiogram and vital signs [7]. A 2023 pilot randomised 194 haemodialysis patients to 1.6 mg Ta1 subcutaneously twice weekly for 8 weeks or to control, with a data safety monitoring board reviewing reported adverse effects [21].

Is either peptide banned in sport?

Sermorelin is. WADA's S2.2.4 names growth hormone releasing factors, GHRH and its analogues including sermorelin, as prohibited at all times, in and out of competition, and the substance is named on both the 2026 and 2027 Lists [5][6]. Thymosin alpha-1 is not named on either List. WADA does name thymosin-beta-4 and its derivatives such as TB-500, which is a different peptide [5][4].