Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
Noticing more hair in the shower drain after starting weight loss injections? You’re definitely not alone. While medications like semaglutide and tirzepatide are known for reducing appetite and supporting significant weight loss, some people report hair shedding along the way. And although it feels alarming, this kind of hair loss is usually a short-term response to rapid changes in weight, nutrition or stress.
Studies show that sudden calorie reduction or fast weight loss can shift more hair follicles into the ‘resting’ phase, which is when shedding happens. This has been observed not just with injections but also after bariatric surgery, crash diets and even periods of emotional stress. On top of that, some people unintentionally eat less protein and fewer micronutrients while on appetite-suppressing medications, which can further affect hair strength.
But here’s the good news: this type of hair loss is almost always reversible. With the right habits and a bit of patience, most people see regrowth within a few months. Below, we’ll break down why it happens, how to reduce the risk and what the typical recovery timeline looks like.
Hair is extremely sensitive to change, which is why rapid weight loss often triggers temporary shedding. Research notes that significant calorie deficits, reduced protein intake and metabolic adjustments can push a higher number of strands into the telogen (resting) phase. This results in drastic hair loss, also called telogen effluvium.
This type of hair loss doesn’t mean your hair follicles are damaged. Instead, the body simply prioritises essential functions, like energy and nutrient distribution, over non-essential processes such as hair growth. Once your body stabilises and nutrient intake improves, the hair cycle usually restarts.
It’s also important to remember that hair responds to both physical and emotional stressors. Weight loss, lifestyle changes and hormonal fluctuations can all contribute to temporary shedding.
Weight loss injections don’t directly cause hair loss, but the changes they trigger can create conditions where shedding is more likely. Here’s how:
Reduced appetite: You may eat less overall, which can mean less protein, iron, zinc and B vitamins. These nutrients are essential for hair health.
Rapid weight loss: Losing weight quickly can signal stress to the body, pushing more hair follicles into the shedding phase.
Shifts in hormones: Weight loss can influence thyroid hormones, insulin and cortisol, which all play roles in the hair growth cycle.
Lower calorie intake: A sustained deficit may reduce the energy your body allocates to hair growth, causing temporary thinning.
Studies looking at post-bariatric patients, who also experience fast weight loss, show similar patterns of shedding, supporting the idea that the weight change itself is the main driver, not the medication.
Supporting hair health while on weight loss medications is absolutely possible, and small daily habits make a big difference.
Hair is mostly made of keratin, a protein. Research shows that inadequate protein intake is a major contributor to telogen effluvium. Aim to include a protein source in every meal, even if your appetite is low.
Iron, zinc, selenium and magnesium play essential roles in hair growth. Lean meats, eggs, leafy greens, legumes, nuts and seeds are excellent options that support overall nutritional balance.
Stress elevates cortisol, which can disrupt the hair growth cycle. Light walking, breathing exercises, journalling or even a relaxing hobby can help regulate stress while supporting overall wellbeing.
Poor sleep affects hormone balance, appetite regulation and recovery. Studies show that adults who sleep 7 to 9 hours have better metabolic health and lower stress levels, both key for hair stability.
Mild dehydration reduces skin and scalp health. Drinking water throughout the day helps support cell function, nutrient transport and overall hair vitality.
Some people benefit from supplements like iron, biotin or collagen, but only if clinically appropriate. Always consult a healthcare provider before starting any supplement.
Most hair loss associated with weight changes is temporary, and regrowth follows a predictable timeline.
Mild shedding for one to three months: This early phase reflects the body adjusting to appetite changes, calorie reduction or rapid weight loss.
Early regrowth is usually visible by three to four months: Soft ‘baby hairs’ often appear around the hairline or part line as follicles transition back into the growth phase.
Noticeable thickening by six months: With consistent nutrition and balanced habits, hair density usually improves around this point.
Full recovery may take nine to twelve months: This varies from person to person, but most people regain full thickness within a year as the hair cycle normalises.
If your hair is thinning, it might be a sign your metabolism is under extra pressure. Read Signs You Have a Slow Metabolism to see whether your body is slowing down in more ways than one.
Hair loss after weight loss injections is more common than people realise, but it’s also almost always temporary. The shedding is typically a response to rapid weight change, reduced nutrient intake or increased physical stress, not a sign of permanent damage.
With steady protein, micronutrient-rich foods, good sleep, hydration and stress management, most people see regrowth within months. And if you’re ever unsure, a clinician can help rule out deficiencies and guide you toward the healthiest approach.
Sudden hair changes can also happen when your body shifts into energy conservation mode. Read Weight Loss Plateau Solutions to understand how metabolic adaptation can affect everything from fat loss to hair health.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.