Can Weight Loss Medication Make You Tired?
If you have started prescription weight loss treatment and suddenly feel more tired than usual, it is reasonable to wonder whether the medication is responsible.
Yes, some prescription weight loss medicines can make some people feel tired.
Fatigue is listed as a common side effect of both semaglutide, used in Wegovy, and tirzepatide, used in Mounjaro.
However, the medicine itself is not always the whole explanation.
Eating considerably less, dehydration, nausea, diarrhoea, poor sleep, changes in blood sugar and other health conditions can all contribute to low energy.
Understanding why you are tired is more useful than simply assuming it is something you need to tolerate.
Is Tiredness a Recognised Side Effect of Weight Loss Medication?
Yes.
Both tirzepatide and semaglutide list fatigue among recognised adverse effects.
With semaglutide, fatigue has been particularly reported while doses are gradually being increased.
Not everyone experiences it.
Some people notice very little difference in their energy levels, while others feel noticeably more tired after starting treatment or moving to a higher dose.
People can respond very differently to the same medicine.
Why Might Weight Loss Medication Make You Feel Tired?
There are several possible reasons.
The medication itself may contribute, but fatigue can also develop indirectly because your appetite, eating habits and fluid intake have changed.
You May Be Eating Much Less
Medicines such as semaglutide and tirzepatide can reduce appetite and help people feel fuller for longer.
For some people, the change can be substantial.
You might suddenly find that:
Meals are much smaller You forget to eat You skip meals because you are not hungry Foods you previously enjoyed seem less appealing You feel full after only a small amount
That can support weight management, but eating dramatically less can also leave you short of energy.
Reduced appetite should not mean trying to eat as little as possible.
Your body still needs adequate nutrition even when your appetite is lower.
Can Eating Too Little Make You Exhausted?
It can.
Weight loss normally involves consuming less energy than your body uses, but a very large reduction is not automatically better.
If your food intake falls dramatically, you may experience:
Tiredness Weakness Poor concentration Feeling cold Headaches Reduced exercise performance Irritability Dizziness
If you are barely eating because you no longer feel hungry, it is worth reviewing what you are actually consuming across the day.
The goal of medical weight management is not starvation.
It is to support safe and sustainable weight reduction while maintaining adequate nutrition.
Could Dehydration Be Making You Tired?
Yes.
This is an important consideration with some weight loss medicines.
Nausea, vomiting and diarrhoea are recognised side effects of both semaglutide and tirzepatide. These symptoms can lead to dehydration if enough fluid is lost or you are unable to drink normally.
Dehydration can cause:
Fatigue Headaches Dry mouth Dizziness Difficulty concentrating Darker urine Feeling lightheaded when standing
You may also simply be drinking less because you are eating less.
Some of our daily fluid intake normally comes from food, so a significant reduction in food intake can affect hydration too.
How Can You Stay Hydrated?
Try to drink regularly throughout the day rather than relying entirely on feeling thirsty.
Water is a straightforward option, but other suitable drinks also contribute to your fluid intake.
If you are experiencing repeated vomiting or diarrhoea, particularly if you are struggling to keep fluids down, speak to a healthcare professional.
Persistent vomiting or significant dehydration should not simply be treated as an expected inconvenience of weight loss medication.
Does Protein Matter During Weight Loss?
Yes.
Protein is particularly useful during weight loss because it contributes to maintaining muscle.
Useful sources include:
Chicken Fish Eggs Lean meat Greek yoghurt Cottage cheese Beans Lentils Tofu
If your portion sizes have become much smaller, try to make the food you do eat nutritionally useful.
Including a source of protein with your main meals is a sensible starting point.
This becomes particularly important if you are losing weight quickly.
Should You Avoid Carbohydrates?
There is usually no need to remove carbohydrates simply because you are trying to lose weight.
Foods such as:
Potatoes Oats Rice Wholegrain bread Pasta Fruit Beans
can provide energy as well as important nutrients.
If you suddenly reduce your total food intake and remove most carbohydrates at the same time, you may find that your energy levels fall.
A balanced eating pattern is generally easier to maintain than unnecessarily eliminating entire food groups.
Can Low Blood Sugar Cause Tiredness?
Yes.
Low blood sugar, known medically as hypoglycaemia, can cause symptoms including:
Weakness Shaking Sweating Dizziness Hunger Confusion Tiredness
The risk is particularly relevant for some people with type 2 diabetes who use weight management medicines alongside insulin or medicines known as sulfonylureas.
Official prescribing information for both tirzepatide and semaglutide warns that the risk of hypoglycaemia can increase when they are used alongside these medicines.
If you have diabetes, changes in appetite, weight or treatment can sometimes mean your other medication needs reviewing.
Do not change prescription diabetes medication yourself unless advised by the healthcare professional managing your treatment.
Can Low Blood Pressure Make You Feel Tired?
It can.
Symptoms of low blood pressure may include:
Weakness Dizziness Lightheadedness Blurred vision Fainting
Tirzepatide weight management trials have reported blood pressure related adverse events, including low blood pressure and postural low blood pressure, although most were mild to moderate.
Weight loss itself may also improve blood pressure.
That is generally positive, but if you already take medicines for high blood pressure, significant weight loss may sometimes mean your treatment needs reviewing.
If you regularly feel dizzy when standing or unusually weak, speak to your healthcare professional.
Can Nausea Make You Feel Exhausted?
Definitely.
Even relatively mild nausea can affect how much you eat and drink.
If it continues for several days, you might gradually consume much less food and fluid than usual.
That can leave you feeling drained.
Nausea, vomiting and diarrhoea are among the most commonly reported gastrointestinal effects of semaglutide and tirzepatide.
If these symptoms are making it difficult to eat or drink adequately, contact the clinician managing your treatment.
Does Tiredness Get Better With Time?
It can.
Some people notice that side effects settle as their body becomes accustomed to treatment.
This may be particularly relevant when starting treatment or after increasing the dose.
Semaglutide product information notes that fatigue has been observed mainly during the period when doses are being increased.
However, this does not mean you should ignore persistent exhaustion.
Severe or prolonged tiredness deserves further assessment.
Another cause may be involved.
Can Losing Weight Too Quickly Make You Tired?
Potentially.
If your weight is falling rapidly because you are barely eating, your nutritional intake may be inadequate.
Very restrictive intake can also make it harder to consume enough protein, vitamins, minerals and other nutrients.
There is no prize for losing weight as quickly as possible.
The aim should be sustainable improvement in health rather than simply chasing the fastest possible change on the scales.
What About Muscle Loss?
When body weight falls, some of the weight lost can come from lean tissue as well as body fat.
This is one reason maintaining muscle is an important part of weight management.
Helpful strategies can include:
Eating adequate protein Remaining physically active Including resistance exercise where appropriate Avoiding unnecessarily extreme food restriction
Resistance exercise does not have to mean heavy bodybuilding.
Body weight exercises, resistance bands, machines and free weights can all contribute.
Could Poor Sleep Be the Real Problem?
Absolutely.
Starting a new medicine at the same time as feeling tired makes it tempting to assume the two are definitely connected.
But sleep should also be considered.
Poor sleep can result from:
Stress Anxiety Irregular sleeping patterns Alcohol Menopause Shift work Children waking during the night Sleep apnoea Excessive screen use late at night
Obstructive sleep apnoea deserves particular attention because it is associated with overweight and obesity and can cause significant daytime fatigue.
If you regularly snore loudly, stop breathing during sleep, wake gasping or remain exhausted despite spending enough time in bed, speak to your GP.
Could Vitamin or Iron Deficiency Cause Tiredness?
Potentially.
Fatigue has many possible causes.
These can include:
Iron deficiency Vitamin B12 deficiency Folate deficiency Vitamin D deficiency Anaemia
That does not mean everyone taking weight loss treatment needs supplements.
Taking supplements without knowing whether you are deficient may not address the real problem.
If fatigue persists, a healthcare professional can decide whether blood tests or further investigation are appropriate.
You can also read our guide:
Vitamin D Deficiency in Northern Ireland: Symptoms, Testing and Supplements
Could an Underactive Thyroid Be Responsible?
An underactive thyroid can also cause tiredness.
Other symptoms may include:
Feeling unusually cold Weight gain Constipation Difficulty concentrating Low mood Dry skin Changes to hair Changes to periods
If these symptoms are present, particularly if they started before your weight management treatment, speak to your GP.
Not every symptom that happens during weight loss is caused by the medication.
What Can Help With Tiredness During Weight Loss Treatment?
What helps depends on why you are tired.
However, several practical checks are worthwhile.
Make Sure You Are Eating Enough
Reduced appetite can make it surprisingly easy to undereat.
Try to maintain regular, balanced meals even if the portions are smaller than before.
Prioritise Protein
Include a good source of protein with meals where possible.
This supports muscle and can help meals feel more satisfying.
Drink Regularly
Keep an eye on your fluid intake, particularly if you are experiencing nausea, vomiting or diarrhoea.
Avoid Extreme Dieting
You do not need to combine prescription weight management medicine with an extremely restrictive diet.
The treatment may already have substantially reduced your appetite.
Keep Moving
Regular walking and general activity can help maintain fitness and routine.
Resistance exercise can also help preserve muscle where appropriate.
Protect Your Sleep
Try to maintain reasonably consistent sleeping and waking times.
If you are getting adequate sleep but remain exhausted, consider whether there could be another cause.
Should You Use Energy Drinks to Deal With Fatigue?
They are unlikely to address the underlying problem.
Caffeine can temporarily increase alertness, but excessive amounts may also:
Affect sleep Increase anxiety Cause palpitations Create a cycle of daytime caffeine and poor sleep at night
Tea or coffee in sensible amounts may be fine for many people.
But if you suddenly require several energy drinks simply to get through the day, it is better to investigate why you are so tired.
Should You Reduce Your Medication Dose?
Do not change a prescribed dose yourself.
If fatigue became significantly worse after your dose was increased, speak to the clinician responsible for your treatment.
They may want to consider:
How long the symptoms have lasted How much you are eating Your fluid intake Other side effects Your current medicines Your treatment dose How quickly you are losing weight Whether another medical issue needs investigating
A higher dose is not automatically a better dose.
Dosing decisions should be made by the prescribing clinician based on the individual patient's circumstances and response to treatment.
When Should You Speak to Your Clinician?
Contact the healthcare professional managing your treatment if tiredness:
Is severe Does not improve Is interfering with everyday activities Began after a dose change and is difficult to manage Occurs alongside persistent vomiting or diarrhoea Is associated with frequent dizziness Comes with symptoms suggesting low blood sugar Continues despite eating and drinking adequately
You should also speak to a healthcare professional if you suspect the tiredness may have another cause.
When Could Symptoms Need Urgent Attention?
Seek urgent medical help if you become seriously unwell.
Particular concerns include:
Being unable to keep fluids down Severe or persistent vomiting Fainting Significant confusion Symptoms of severe dehydration Severe and persistent abdominal pain Difficulty breathing Swelling involving the face, lips, tongue or throat
These should not simply be assumed to be normal weight management side effects.
Do Not Automatically Blame the Medication
This is worth emphasising.
Fatigue beginning after treatment starts may be related to the medicine.
But tiredness can also result from:
Poor sleep Stress Infection Anaemia Iron deficiency Thyroid problems Vitamin deficiencies Sleep apnoea Low mood Other medicines Eating too little Dehydration
Persistent fatigue should be properly considered rather than automatically blamed on weight loss treatment.
The Bottom Line
Weight loss medication can make some people feel tired.
Fatigue is a recognised common side effect of both semaglutide and tirzepatide.
However, the cause may also be indirect.
Eating substantially less, dehydration, digestive side effects, poor sleep or changes in blood sugar can all contribute.
Making sure you are eating adequately, getting enough protein, drinking regularly and protecting your sleep may help.
If tiredness is persistent, severe or accompanied by other concerning symptoms, speak to the clinician managing your treatment rather than simply pushing through it.
Keltoi Wellness is a doctor led telehealth service providing weight management support for adults in Northern Ireland. Any prescription treatment is subject to an individual clinical assessment, with prescribing decisions made independently by the treating doctor.
Health information provided by Keltoi Wellness is for general education and does not replace individual medical advice, diagnosis or treatment.