GLP-1 medicines such as semaglutide (Wegovy) and tirzepatide (Mounjaro) have changed the weight-loss conversation in the UK.
But the injection itself is only one part of the picture.
If you are prescribed GLP-1 therapy, you need to track more than the number on the scales. Your appetite, waist measurement, blood sugar, medication, nutrition, side effects and general health all matter. Good tracking helps you and your prescriber understand what is happening , and gives you useful information for your next GP appointment.
TL;DR:
- Before treatment: Record your weight, height, BMI, waist measurement, blood pressure, medical history and current medicines.
- Consider baseline blood tests: These may include HbA1c, cholesterol, kidney function, liver function, full blood count and thyroid tests, depending on your situation.
- During treatment: Track weight trends, waist measurement, dose changes, appetite, hydration, bowel habits and side effects.
- Get medical help quickly: Severe or persistent abdominal pain, repeated vomiting, signs of dehydration or sudden vision changes need urgent attention.
- After treatment: Keep monitoring your weight, health conditions, eating patterns and activity. NICE recommends regular support for at least one year after stopping weight-management medicine.
- At-home testing can provide useful data, but it does not replace your prescriber, GP or clinical follow-up.
What should you track before, during and after GLP-1 therapy? Track your baseline measurements, relevant blood markers, weight trend, waist measurement, blood pressure, blood sugar where appropriate, nutrition, hydration, dose changes and side effects. Continue monitoring your health and weight after treatment, with support from your GP or prescriber.
What are GLP-1 medicines used for in the UK?
GLP-1 medicines mimic a natural hormone involved in appetite and blood sugar control. They can help you feel fuller for longer and reduce hunger.
In the UK, semaglutide, tirzepatide and liraglutide are prescription medicines. They are intended for specific medical uses and should be prescribed after a proper assessment. The MHRA explains how GLP-1 medicines are licensed and the risks of buying them from unregulated sellers.
They are not a quick cosmetic fix. They should be used alongside appropriate food, physical activity and behavioural support.
The exact eligibility rules depend on the medicine, your BMI, related health conditions and the service providing treatment. For example, NICE guidance on tirzepatide sets out specific criteria for its use in weight management.
Think of GLP-1 therapy like adding cruise control to a car. It may help manage speed, but you still need to know where you are going, watch the road and respond to warning lights.
STEP 1: What to track before starting GLP-1 therapy
Before your first dose, create a clear starting point. This is your baseline.
Record your basic measurements
Write down:
- Weight
- Height
- BMI
- Waist measurement, where relevant
- Blood pressure
- Heart rate, if advised by your healthcare professional
Your baseline allows you to compare changes over time. It also gives your prescriber a fuller picture than a single weigh-in.
NICE’s practical prescribing guide recommends recording height, weight and BMI. It also says that healthcare professionals may assess waist measurement, blood pressure, lipid profile, HbA1c, blood glucose and other tests based on your medical history and clinical circumstances.
Review your health history and medicines
Tell your prescriber about:
- Type 2 diabetes or pre-diabetes
- High blood pressure or cholesterol
- Kidney, liver or gallbladder problems
- Previous pancreatitis
- Digestive conditions
- Eating disorders or mental health concerns
- Pregnancy plans or breastfeeding
- Every medicine and supplement you take
Do not stop or change prescribed medicine without speaking to your GP or prescriber.
This matters because GLP-1 medicines can affect blood sugar, digestion and the absorption of some oral medicines. If you take insulin or a sulfonylurea for diabetes, your blood sugar may need closer monitoring.
Consider useful baseline blood tests
There is no single blood panel that everyone must have before starting a GLP-1 medicine. Your prescriber will decide what is suitable.
Depending on your health history, baseline tests may include:
- HbA1c: A picture of your average blood sugar over the previous few months
- Lipid profile: Cholesterol and related blood fats
- Kidney function: Often including creatinine and eGFR
- Liver function: Including markers such as ALT and AST
- Full blood count: A broad look at red cells, white cells and platelets
- Thyroid function: If symptoms or medical history make this relevant
- Nutritional markers: Such as ferritin, vitamin B12, folate or vitamin D if intake is limited or deficiency is a concern
Your blood results are like the “before” photo in a renovation project. Without them, it is harder to tell whether a later change was already present or developed during treatment.
A GLP-1 and nutrient deficiency guide in the Vitall Check Health Hub explains why reduced appetite can make nutritional intake worth monitoring.
STEP 2: What to track during GLP-1 therapy
The early weeks often involve dose adjustments. This is when keeping a simple record is especially useful.
Track your weight as a trend
Weigh yourself consistently if your healthcare professional recommends it. Try to use similar conditions each time, such as the same day and time of day.
Do not judge treatment by one reading. Weight can change because of fluid, digestion, clothing, exercise and menstrual cycle changes.
Record:
- Your current weight
- Change from your starting weight
- The date of each measurement
- Any major changes in appetite or food intake
For tirzepatide, NICE recommends follow-up every four weeks during dose titration. After six months on the highest tolerated dose, the prescriber reviews the percentage of weight lost and considers whether continuing treatment is suitable.
That decision belongs with your prescriber. Do not increase, reduce or stop your dose based on an online calculator or someone else’s experience.
Track your waist measurement
Weight does not tell the whole story. Waist measurement can provide another way to follow change, particularly where it is clinically relevant.
Use the same method each time. Measure in a consistent position and record the date. If you are unsure how to do this, ask your GP or follow the NHS guide to waist-to-height ratio.
Track side effects and hydration
Common side effects include nausea, vomiting, diarrhoea and constipation. These can be more noticeable during dose increases.
Keep a short daily note of:
- Nausea or vomiting
- Diarrhoea or constipation
- Abdominal pain
- How much you are drinking
- Whether you are managing regular meals
- Changes in energy or mood
Drink enough fluid for your personal needs, especially if you have vomiting or diarrhoea. Dehydration can become serious and may affect kidney function.
Seek urgent medical help for severe, persistent abdominal pain, particularly if it spreads to your back or occurs with vomiting or fever. This can be a warning sign of pancreatitis. The MHRA’s GLP-1 safety advice also highlights serious dehydration, sudden vision changes and other safety concerns.
Tell your healthcare team that you take a GLP-1 medicine before surgery or deep sedation.
Track blood sugar when relevant
If you have diabetes, follow the monitoring plan given by your diabetes team.
You may need closer HbA1c or blood glucose monitoring during dose changes. This is particularly important if you also use insulin or a sulfonylurea, because your treatment may need adjusting to reduce the risk of hypoglycaemia.
For people without diabetes, routine blood glucose checks are not automatically needed. Ask your GP or prescriber what applies to you.
Track your nutrition and strength
A smaller appetite can make it harder to eat enough protein, fibre, vitamins and minerals. You do not need to turn every meal into a spreadsheet, but note whether you are managing a varied diet.
Track:
- Foods you tolerate well
- Foods that worsen nausea or reflux
- Your usual protein sources
- Fruit and vegetable intake
- Any new food avoidance
- Changes in strength or exercise tolerance
If you are training, be particularly careful not to confuse low food intake, dehydration or poor recovery with a medication problem. Discuss ongoing symptoms with your GP, prescriber or a qualified dietitian.
Can at-home blood testing help during GLP-1 therapy?
It can provide useful information for an informed GP conversation, especially if you want to compare a baseline with a later result.
A panel covering areas such as blood sugar, liver markers, kidney markers, blood count, inflammation or nutritional status may be relevant in some situations. The right choice depends on your health, medicines and reason for testing.
The Advanced Organ Health & Immune Profile, for example, lists markers covering liver function, kidney-related measures, blood counts and inflammation. It is not a GLP-1 prescribing or monitoring service, so discuss what you need with your healthcare professional first.
If you choose an at-home test:
- Warm your hands.
- Drink water before collection, unless you have been told to restrict fluids.
- Avoid heavy exercise beforehand if the instructions advise this.
- Follow the official Vitall Check sample collection guide.
- Post the sample as instructed.
Finger-prick testing can be straightforward, but some people find collection difficult. That is normal. If you cannot collect enough blood or feel faint, stop and follow the kit instructions for support.
STEP 3: What to track after stopping GLP-1 therapy
Do not treat stopping as the end of monitoring.
Your prescriber should guide any decision to stop, switch or restart treatment. After stopping, continue recording:
- Weight and waist measurement
- Appetite and eating patterns
- Physical activity
- Blood pressure, where relevant
- Blood sugar if you have diabetes
- Symptoms linked to previous health conditions
- Any nutritional concerns
- Your mood and relationship with food
Weight regain is not a personal failure. Obesity can be a long-term, relapsing condition, and appetite may change when medicine is stopped.
NICE quality standard QS212 says people stopping weight-management medicines should receive advice and support to maintain changes, with regular monitoring for a minimum of one year.
Think of this stage as moving from assisted driving to independent driving. You still need a route, regular checks and help when the dashboard shows a warning.
Pregnancy, contraception and GLP-1 medicines
GLP-1 medicines should not be used during pregnancy or breastfeeding.
The wash-out period before planned pregnancy differs by medicine:
- Semaglutide: Stop at least two months before trying to conceive.
- Tirzepatide: Stop at least one month before trying to conceive.
Tirzepatide may also affect how well the oral contraceptive pill is absorbed after starting treatment or increasing the dose. Ask your prescriber or pharmacist about additional contraception.
The MHRA provides current guidance on GLP-1 medicines, pregnancy and contraception.
Summary: build your own GLP-1 health record
The best GLP-1 tracking plan is simple enough to follow and detailed enough to be useful.
Before treatment, record your starting point. During treatment, track trends, side effects, hydration, nutrition and relevant blood markers. After stopping, continue monitoring and use the support available to you.
At-home testing can help translate raw laboratory data into plain-English insights. It can support better conversations with your GP, but it does not diagnose, prescribe or replace clinical care.
FAQ
Q: Should I get a blood test before starting Wegovy or Mounjaro? A: Ask your prescriber. There is no single test required for everyone, but baseline checks such as HbA1c, cholesterol, kidney function, liver function, full blood count or thyroid tests may be appropriate depending on your health and medicines.
Q: How often should I have blood tests while taking a GLP-1 medicine? A: There is no universal schedule for everyone. Your prescriber will decide based on your medical history, dose changes, diabetes status, symptoms and previous results. NICE recommends four-weekly follow-up during tirzepatide dose titration.
Q: Can an at-home blood test replace my GP or prescriber? A: No. It can provide useful screening information and help you arrive informed for your next appointment, but it does not provide a diagnosis, treatment or prescription.
Q: What should I do if I have severe stomach pain while taking a GLP-1 medicine? A: Seek urgent medical help, particularly if the pain is persistent, spreads to your back or occurs with vomiting or fever. Do not wait for an at-home test result.
Author
Vitall Check Editorial Team
The Vitall Check Editorial Team is dedicated to empowering individuals with evidence-based health information and clear, actionable insights. Every article is researched using peer-reviewed journals and official health resources, reflecting our commitment to the same high standards of accuracy as our laboratory testing services. Our goal is to make proactive wellness accessible, data-driven, and transparent.
Disclaimer: Vitall Check is not CQC registered. The content provided is for general information only, does not provide a diagnosis, and does not replace advice from a qualified healthcare professional. Our services do not include treatment, prescription, or medical advice that falls under CQC-regulated activities. Always consult with your GP or a qualified clinician before making significant changes to your healthcare regimen.
