Retatrutide and hair loss is an emerging concern as this investigational triple receptor agonist advances through clinical trials. Retatrutide targets GLP-1, GIP, and glucagon receptors simultaneously, producing substantial weight loss in phase 2 studies. Although hair loss has not been formally confirmed as a direct adverse effect of retatrutide, the significant and rapid weight reduction it induces may trigger telogen effluvium — a temporary, stress-related shedding pattern well recognised with other weight loss medicines. This article examines the current evidence, relevant comparisons with licensed agents, and practical guidance for those affected.

Does Retatrutide Cause Hair Loss?

Hair loss has not been formally confirmed as a direct adverse effect of retatrutide in published trial data, but rapid weight loss associated with the drug may trigger telogen effluvium, a temporary shedding condition.

Retatrutide is an investigational triple receptor agonist currently in clinical development. It targets the glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon receptors simultaneously. As of the time of writing, retatrutide has not received marketing authorisation from the Medicines and Healthcare products Regulatory Agency (MHRA) or the European Medicines Agency (EMA), and no UK Summary of Product Characteristics (SmPC) exists for it. It is therefore not available as a licensed medicine in the UK outside of regulated clinical trials.

Because retatrutide remains in clinical trials, its full side-effect profile has not been comprehensively established through post-marketing surveillance. Hair loss — medically referred to as telogen effluvium when associated with physiological stress or rapid weight change — has not been formally listed as a confirmed adverse effect of retatrutide in published trial data. However, there is a well-recognised association between significant, rapid weight loss and temporary hair shedding, regardless of the method used to achieve that weight loss.

It is important to distinguish between hair loss that may be directly attributable to the drug itself and hair loss that arises as a consequence of the metabolic and nutritional changes accompanying rapid weight reduction. Because no UK SmPC exists for retatrutide, definitive safety labelling is not yet available. Patients and clinicians should nonetheless remain alert to this possibility, particularly given the substantial weight loss retatrutide has produced in phase 2 trial settings (see the New England Journal of Medicine, 2023). Any suspected side effects in trial participants should be reported to the trial investigator and, where appropriate, via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk.

How Weight Loss Medicines Can Affect Hair Growth

Rapid weight loss can shift hair follicles prematurely into the telogen (resting) phase, causing diffuse shedding typically noticed two to four months after the triggering event.

To understand why weight loss medicines may be associated with hair shedding, it helps to understand the normal hair growth cycle. Hair follicles cycle through three phases: anagen (active growth), catagen (transition), and telogen (resting and shedding). Under normal circumstances, approximately 85–90% of hairs are in the anagen phase at any given time. When the body experiences significant physiological stress — such as rapid caloric restriction, nutritional deficiency, or substantial weight loss — a disproportionate number of follicles can shift prematurely into the telogen phase. This results in diffuse shedding, typically noticed two to four months after the triggering event.

This phenomenon, known as telogen effluvium, has been reported in association with several weight loss medicines. Semaglutide 2.4 mg (Wegovy) lists alopecia as an uncommon adverse reaction (affecting between 1 in 100 and 1 in 1,000 users) in its UK SmPC. Tirzepatide (Mounjaro) — a dual GIP/GLP-1 receptor agonist — similarly lists alopecia in its product information. It is important to note that tirzepatide acts on both GIP and GLP-1 receptors and is not a GLP-1 receptor agonist alone. The MHRA's Yellow Card reporting scheme continues to collect post-marketing data on such effects for all licensed medicines.

Key nutritional factors that may contribute to hair loss during rapid weight loss include:

• Protein deficiency — hair is primarily composed of keratin, a structural protein

• Iron deficiency — a common consequence of reduced dietary intake

• Zinc insufficiency — plays a role in follicle health, though routine testing is not universally recommended and excess zinc can cause copper deficiency

• Overall caloric restriction — redirects energy away from non-essential functions such as hair growth

Note that biotin (vitamin B7) is widely marketed for hair health, but evidence for its benefit in the absence of confirmed deficiency is limited. High-dose biotin supplementation can also interfere with certain laboratory assays, including thyroid function tests and troponin assays, potentially producing misleading results; this is the subject of an MHRA Drug Safety Update.

Because retatrutide produces substantial weight loss in clinical trials, the risk of nutritionally mediated telogen effluvium may be correspondingly relevant, though this remains to be confirmed in larger datasets.

What the Clinical Trial Evidence Shows

Phase 2 retatrutide trial data reported gastrointestinal effects as the most common adverse events; hair loss was not prominently recorded, though larger phase 3 datasets may reveal delayed-onset effects.

Phase 2 clinical trial data for retatrutide, published in the New England Journal of Medicine in 2023, demonstrated mean weight reductions of approximately 17–24% of body weight over 48 weeks, depending on dose — results that exceed those seen with currently licensed agents in comparable timeframes. The trial enrolled adults with obesity and reported that the most common adverse effects were gastrointestinal in nature, including nausea, vomiting, diarrhoea, and constipation. These are consistent with the class effects observed across GLP-1 receptor agonist medicines.

Hair loss was not prominently reported as a primary adverse event in the published phase 2 data. However, clinical trials are not always powered or designed to capture lower-frequency or delayed-onset adverse effects such as telogen effluvium, which may emerge weeks to months after treatment initiation. Phase 3 trials are ongoing, and a more complete safety profile — including any association with hair shedding — will emerge as larger datasets are analysed and regulatory submissions are made.

For context, hair loss has been reported in post-marketing data and UK SmPCs for semaglutide 2.4 mg and tirzepatide, both of which share mechanistic similarities with retatrutide. Given the substantial weight loss retatrutide produces, it is plausible that nutritionally driven hair shedding may occur in some individuals — though this should be understood as a hypothesis based on the known effects of rapid weight loss rather than a confirmed drug-specific effect. Participants in ongoing phase 3 trials should report any new hair shedding to their trial investigators, as this information contributes to the emerging safety evidence base and may be reportable under the trial protocol.

When to Speak to a GP or Pharmacist

Retatrutide trial participants should report hair shedding to their trial investigator; those on licensed weight loss medicines should see a GP if shedding persists beyond three to six months or is accompanied by systemic symptoms.

Because retatrutide is not yet licensed in the UK, individuals will only encounter it within the context of a regulated clinical trial. If you are participating in a retatrutide trial and notice increased hair shedding, the first step is to inform your trial investigator or study nurse, as this may constitute a reportable adverse event under the trial protocol. Suspected side effects may also be reported directly via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk) or the Yellow Card app.

For those using other licensed weight loss medicines — such as semaglutide 2.4 mg (Wegovy) or tirzepatide (Mounjaro) — and experiencing hair loss, it is advisable to speak to a GP or pharmacist if:

• Hair shedding is noticeably increased when washing or brushing

• Shedding persists for more than three to six months

• There is visible thinning or patchy hair loss

• Hair loss is accompanied by other symptoms such as fatigue, cold intolerance, or brittle nails, which may suggest an underlying thyroid or nutritional deficiency

The following are red flag features that warrant prompt medical review and possible referral to a dermatologist:

• Painful, inflamed, or scarring scalp changes

• Rapidly progressive or patchy hair loss, including loss of eyebrows or eyelashes

• Suspected tinea capitis (scalp ringworm), particularly in children

• Systemic symptoms suggesting an underlying condition

A GP can arrange relevant investigations, which should be guided by clinical history and examination. Baseline tests typically include:

• Full blood count — to assess for anaemia

• Serum ferritin and iron studies — iron deficiency is a common and treatable cause

• Thyroid function tests (TSH) — hypothyroidism can cause hair loss independently

• Coeliac screen — if iron deficiency is identified without an obvious dietary cause

Further tests such as vitamin D, vitamin B12, folate, or zinc levels should be requested only where clinically indicated, rather than as a matter of routine. Suspected scarring or inflammatory alopecia warrants prompt referral to a dermatologist. The Primary Care Dermatology Society (PCDS) and NHS UK provide further guidance on the assessment of diffuse hair loss.

It is rarely necessary to discontinue weight loss treatment solely on account of hair shedding, as telogen effluvium is typically self-limiting. However, a clinician should guide any decision to adjust or stop treatment, weighing the benefits of continued therapy against the patient's concerns and overall wellbeing.

Managing Hair Loss During Treatment

Ensuring adequate protein intake (1.0–1.2 g per kg body weight per day) and correcting confirmed nutritional deficiencies are the most important steps in managing hair shedding during weight loss treatment.

For individuals experiencing hair shedding during weight loss treatment, a number of practical strategies can help minimise its severity and support recovery. The most important intervention is ensuring adequate nutritional intake, particularly of protein. Protein requirements during active weight loss are typically in the range of 1.0–1.2 g per kilogram of body weight per day, though individual needs vary; a GP or registered dietitian can provide personalised guidance based on clinical context. This is broadly consistent with guidance from the British Dietetic Association (BDA) and European Society for Clinical Nutrition and Metabolism (ESPEN). Prioritising protein-rich foods — such as eggs, lean meat, fish, legumes, and dairy — can help preserve follicle health during periods of caloric restriction.

If dietary intake is insufficient, a GP or registered dietitian may recommend targeted supplementation. Supplements should only be used where a deficiency has been confirmed or is clinically suspected:

• Iron — only if deficiency is confirmed on blood testing, as excess iron carries its own risks

• Zinc — supports keratin production and follicle cycling, but should not be taken in high doses as excess zinc can cause copper deficiency

• Biotin — widely marketed for hair health, but evidence for benefit in the absence of confirmed deficiency is limited; importantly, high-dose biotin can interfere with certain laboratory assays (including thyroid and cardiac tests), so supplementation should be disclosed to clinicians before blood tests are taken

• A broad-spectrum multivitamin — may serve as a general nutritional safety net during caloric restriction, but is not a substitute for a balanced diet

From a hair care perspective, gentle handling of hair during periods of shedding is advisable. Avoiding excessive heat styling, tight hairstyles, and harsh chemical treatments can reduce mechanical stress on already-vulnerable follicles.

Topical minoxidil is licensed in the UK for androgenetic alopecia (pattern hair loss). Its use in telogen effluvium is off-label and should be discussed with a GP or dermatologist before use, who can advise on whether it is appropriate in an individual's circumstances.

Telogen effluvium associated with weight loss most commonly improves once the underlying trigger — rapid weight loss or nutritional deficiency — is addressed. Hair regrowth typically begins within three to six months of the shedding phase in most cases, though some individuals experience a more prolonged course lasting beyond six months (chronic telogen effluvium). Patients should be reassured that this form of hair loss does not indicate permanent follicle damage, and that with appropriate nutritional support and management of any underlying deficiencies, improvement is the expected outcome for the majority of people.

Frequently Asked Questions