Nour Mansour, a 28-year-old mother of twin daughters, experienced significant weight loss—over three stone in less than seven months—after using Mounjaro, which initially boosted her confidence. However, six months into her weight loss journey, she noticed an alarming side effect: severe hair shedding. Her once full, hip-length hair began to fall out in clumps, transforming from glossy and thick to dry and frizzy, with noticeable thinning at her temples. To conceal this, Nour frequently wore caps and headbands.

Hair thinning and shedding have been reported by many women as a side effect of rapid weight loss or hormonal changes associated with medications like Mounjaro. However, experts like Dr. David Fenton, a consultant dermatologist and hair loss specialist, suggest that the medication itself is not the direct cause. Instead, rapid weight loss or sudden dietary shifts can lead to deficiencies in essential nutrients required for healthy hair growth, including iron, vitamin B12, folate, zinc, and vitamin D. When individuals lose their appetite and reduce food intake, they risk missing out on these vital vitamins. A lack of protein is also a significant factor, as hair is primarily composed of keratin—a fibrous protein crucial for its structure. Insufficient protein can render hair weak and brittle.

Other side effects reported by GLP-1 users, such as brittle fingernails and slowed nail growth, are similarly linked to these nutritional deficiencies. Dr. David Strain, a diabetes expert, highlighted that while closely monitored participants in clinical trials adhere to nutrient-rich diets, many real-world users lack awareness of how to meet their nutritional needs or which supplements are necessary for good health.

Dr. Fenton recommends a blood test for anyone concerned about hair loss, particularly for vegans and vegetarians. To boost iron intake, he suggests consuming red meat, dark leafy greens like kale and spinach, nuts, and seafood. Dairy products such as yogurt and kefir, along with eggs and wholegrains, are good sources of zinc. Vitamin B12, predominantly found in animal products, is also readily available in supplement form.

Normally, approximately 90 percent of hair follicles are in a growth phase, with 10 percent resting. However, when the body experiences stress from factors like illness or significant weight loss, this cycle shifts, causing a higher percentage of follicles to enter the shedding phase. This condition is known as telogen effluvium, and its severity increases with the amount and speed of weight loss. Similar to postpartum hair loss, this issue typically resolves over time. Nevertheless, certain steps can help minimize damage, including slowing down the rate of weight loss to reduce bodily stress. Nour Mansour experienced a positive turnaround after consulting her GP, beginning a supplement regimen, and focusing on a healthy diet, which successfully halted the shedding.