Tiredness and hair loss with Ozempic or Mounjaro: why it happens and what may help

Why does tiredness occur?

Eating smaller amounts, sometimes with a marked calorie deficit, leaves little energy available, especially if the nutrients that support it are also lacking. In a study of more than 461,000 adults starting a GLP-1, most of whom had type 2 diabetes, more than one in five people had a diagnosed nutritional deficiency after a year [2].

The medicine does not alter the anatomy of the digestive system or the absorption of nutrients [1]. The risk comes from eating less, nausea, aversions to certain foods and an unplanned diet [1]. That is why the main focus is on food.

Not all tiredness is nutritional. Poor sleep, drinking too little water when nausea reduces your thirst, or cutting back heavily on bread, rice or potatoes can also explain it. Other causes, such as an underactive thyroid or anaemia with another cause, can be ruled out by your doctor.

Why does more hair fall out?

The most common cause is telogen effluvium. Some of your hair enters the shedding phase at the same time, weeks or months after rapid weight loss or a shortfall in protein, iron or zinc. It can be worrying, but it does not leave bald patches and is usually temporary.

A meta-analysis of 17 studies published in 2026 found that people taking a GLP-1 have around a 40% higher risk of hair loss than those who do not [3]. For telogen effluvium, the increase was around 76% [3]. The authors mainly attribute this to the lack of nutrients that can accompany weight loss [3].

Which deficiencies should be monitored, and what blood tests are needed?

In that study, vitamin D deficiency was the most common at twelve months, at 13.6% [2]. This was followed by anaemia due to nutritional deficiencies, at 4.0%, and deficiency of B vitamins, at 2.6% [2]. Malnutrition due to a lack of protein and energy was rare, at 0.6% [2].

These were diagnoses recorded in medical records, so a mild deficiency may go undetected without a blood test. Iron, B vitamins and protein all have a lot to do with energy and hair.

The European Food Safety Authority sets adult reference values of 11 to 16 mg of iron a day [4]; 16 mg is for women before the menopause. For vitamin D, the value is 15 µg [5], and for B12 it is 4 µg [6]. These figures are for healthy populations, and your doctor or dietitian will interpret your blood test results.

You do not need to wait for clear symptoms before asking for a blood test. If you have been eating much less than usual for several weeks, it makes sense to arrange one sooner, even if the tiredness is still mild.

What to eat to help you feel better

When your appetite is low, it helps most to include protein at every meal, even if the portion is small. Eggs, fish, lean meat, pulses, dairy or tofu can all work. The exact amount can be tailored in a consultation; you can find the full guidance in protein and muscle with a GLP-1.

For iron, having pulses, meat or fish with a citrus fruit or pepper in the same meal improves absorption. Oily fish, eggs and dairy, or an unsweetened fortified soya drink, provide vitamin D and B12. Vitamin D also depends on sunlight, and spending a little time with your face and arms in the light can help.

Avoiding the removal of whole food groups is the other half of the approach. The more you restrict variety to reduce calories, the easier it is to miss out on one of these nutrients.

When your appetite is low, every bite counts: start with protein and variety, even if the portion is small.

What should I do if I can only manage half a plate?

Start with the part of the meal that contains protein and iron, and leave the side for later. If you feel full before finishing, the rest is easier to make up at another sitting.

Spread your food across four or five small meals if three larger meals feel like too much. Dairy, a soya drink or a hard-boiled egg between meals can fill the gap without making you eat a whole plate.

What questions come up in consultations?

• “Does this mean something is wrong with the treatment?” Almost never. We first look at what and how much you are eating.
• “Do I need to stop taking the medicine?” The person who prescribes it will assess that. In most cases, adjusting your food is enough.
• “Should I take a multivitamin just in case?” It is better to have a blood test before taking supplements without knowing whether you need them; if something is lacking, you can be advised on what to take.
• “How long will it take before I notice an improvement?” Energy usually improves sooner. Hair takes longer, as it follows its own growth cycle.
• “Will my hair stay like this?” With telogen effluvium, hair usually grows back once the cause is addressed, although it takes months to notice.

When to seek advice instead of waiting for it to improve on its own

If the tiredness is mild and improves when you adjust your diet, no further action is needed. Make an appointment if it does not improve over a few weeks, if your hair falls out in clumps or patches, or if other symptoms appear.

At that point, it is not just a matter of portion sizes, and your doctor can review it with a full set of blood tests. You could start by mentioning it to the person who prescribes your medicine or to your dietitian.