Key takeaways
- A family history of medullary thyroid cancer or MEN 2 is a reason not to take these medicines.
- Pregnancy and breastfeeding are reasons not to take them. Semaglutide is usually stopped at least two months before trying to conceive.
- Tirzepatide can make birth control pills less reliable for a few weeks after starting and after each dose increase.
- Past pancreatitis, gallbladder problems, diabetic retinopathy, kidney disease and gastroparesis need individual assessment.
- Always tell your doctor and any surgeon or dentist that you take one of these medicines.
Who should definitely not take them?
Part of my job is saying "no" sometimes. Not often, but when the history says no, I say it plainly. These are the clear reasons.
MedlinePlus, the US National Library of Medicine's drug information service, and the NHS list a small number of clear reasons not to use semaglutide or tirzepatide:
- Personal or family history of medullary thyroid cancer. Both medicines caused thyroid tumours in rats. It is not known whether they do so in humans, but the risk is not worth taking in this group.
- Multiple Endocrine Neoplasia type 2 (MEN 2). A rare inherited condition linked with medullary thyroid cancer.
- Allergy to the medicine or to another GLP-1 medicine.
- Pregnancy. There is not enough information to show these medicines are safe for a baby.
- Breastfeeding. The NHS notes semaglutide passes into breast milk.
That is very important to understand: "thyroid problems" is not the same as thyroid cancer. A common underactive thyroid, on treatment and stable, does not by itself rule out these medicines. What matters is any history of thyroid cancer, nodules or thyroid surgery in you or your family. See thyroid and weight myths.
Which conditions need extra caution?
These are not automatic "no" answers, but they need a careful conversation and sometimes a specialist's input.
| Condition | Why it matters | What usually happens |
|---|---|---|
| Past pancreatitis | The NHS says semaglutide may be unsuitable if you have had acute pancreatitis | Usually avoided; any decision needs specialist input |
| Gallstones or gallbladder disease | Rapid weight loss raises gallstone risk | Discuss history; watch for pain under the right ribs |
| Diabetic retinopathy | Rapid sugar improvement can worsen eye disease in some people | Eye check and closer monitoring if you have diabetes |
| Kidney disease | Vomiting and diarrhoea can cause dehydration, which strains the kidneys | Kidney tests before and during treatment |
| Severe stomach problems such as gastroparesis | These medicines slow stomach emptying further | Often avoided |
| Diabetes on insulin or sulfonylureas | Risk of low blood sugar | Diabetes medicines may need lowering |
| Current or past eating disorder | Appetite suppression can worsen disordered eating | Needs careful specialist assessment |
| Upcoming surgery or procedure | Slower stomach emptying matters for anaesthesia | Tell your surgeon, anaesthetist or dentist |
What about pregnancy, contraception and fertility?
This matters for many women in their 20s and 30s, especially those with PCOS, where weight loss can sometimes improve ovulation.
- Planning a pregnancy. The NHS and MedlinePlus advise stopping semaglutide at least two months before trying to conceive.
- Contraception. If there is a chance of pregnancy, reliable contraception is needed while on treatment.
- Tirzepatide and the pill. MedlinePlus states that tirzepatide may reduce the effectiveness of hormonal contraceptives, and your doctor may suggest another method for four weeks after starting and for four weeks after each dose change.
- If you become pregnant while taking either medicine, contact your doctor straight away.
For more, read weight loss medicine and PCOS.
Is it safe for older adults or people with low muscle?
Age alone is not a barrier, but frailty is a concern. In older adults, losing weight without protecting muscle can affect strength, balance and independence. Anyone over 60, or anyone who already has low muscle mass, needs a plan with enough protein and supervised strength training, and a slower pace. See weight loss after 40 and muscle loss on weight loss injections.
What should you tell your doctor before starting?
Bring a written list. Your doctor should ask about all of these, but it helps to be prepared. Memory is not at its best in a consult room.
- Any thyroid cancer, thyroid nodules or thyroid surgery in you, your parents, brothers or sisters.
- Pancreatitis, gallstones or gallbladder removal.
- Diabetes, its treatment, and any eye problems.
- Kidney or liver disease.
- Stomach problems, reflux or digestive conditions.
- Any history of eating disorders, binge eating or very restrictive dieting.
- Pregnancy, breastfeeding, or plans to conceive.
- All medicines and supplements, including contraceptive pills and ayurvedic or herbal products.
- Any planned surgery or dental procedure.
See, what happens is, a good assessment sometimes ends with "not for you", and that is a proper medical outcome, not a failure. For the tests that usually go with this history, see which tests you need before starting weight loss medicine.
Which warning signs mean stop and get help?
Contact a doctor urgently, or go to a hospital, if you develop:
- Stomach pain that does not go away, sometimes spreading to the back, with or without vomiting.
- Swelling of the face, lips or throat, hives, or difficulty breathing or swallowing.
- Yellowing of the skin or eyes, fever or pale stools.
- Much less urine than usual, or swelling of the legs.
- Sudden vision changes.
- A lump or swelling in the neck, hoarseness or trouble swallowing.
- Fast heartbeat or dizziness that does not settle.
How I approach this at Dr Tvacha
Every Endgame Weight Programme begins with a Rs 499 eligibility video consult with me, where I go through your personal and family history before any medicine is even discussed. If treatment is not right for you, I will tell you plainly and suggest other options. If it is, you get the fee in writing, fixed monthly reviews with me and WhatsApp support for side effects. Details are on the weight loss page.
Frequently asked questions
Can I take weight loss injections if my mother had thyroid problems?
It depends on the type. A common underactive or overactive thyroid in a parent does not usually rule out treatment. A family history of medullary thyroid cancer, or of MEN 2 syndrome, does. If you are unsure what kind of thyroid problem a relative had, try to find out, and mention any thyroid surgery or cancer to your doctor before starting.
Can I take weight loss injections while trying to get pregnant?
No. These medicines are not used in pregnancy, because there is not enough information to show they are safe for the baby. The NHS advises stopping semaglutide at least two months before trying to conceive. If you have PCOS and are planning a pregnancy, discuss the timing with both your weight doctor and your gynaecologist.
Does tirzepatide affect the birth control pill?
It can. MedlinePlus states that tirzepatide may reduce the effectiveness of hormonal contraceptives, and doctors may suggest another method, such as condoms, for four weeks after starting and for four weeks after each dose increase. Please discuss your contraception with your doctor before you begin treatment, not after.
I had gallstones before. Can I still take these medicines?
Possibly, but it needs a careful discussion. Rapid weight loss raises the risk of gallstones, and gallbladder problems have been reported with these medicines. Your doctor will ask whether your gallbladder has been removed and whether you still have symptoms, and may suggest an ultrasound. Report any pain under the right ribs promptly.
Should I tell my dentist or surgeon that I take weight loss injections?
Yes. These medicines slow stomach emptying, which matters when you receive anaesthesia or sedation. MedlinePlus advises telling your surgeon or dentist before any procedure, and they may give specific instructions about the dose before surgery. Do not stop or skip doses on your own without guidance.
Written by
Dr Amit KarkhanisAesthetic Physician · MBBS, Dip. Dermatology (UK) · Reg. No. 2001/02/1124Founder of Dr Tvacha, practising in Thane since 2005. Leads the weight loss and hair programmes.
Sources
- Semaglutide injection (MedlinePlus, US National Library of Medicine)
- Tirzepatide injection (MedlinePlus, US National Library of Medicine)
- Semaglutide (NHS medicines)
- Monitoring patients on GLP-1 agonists (Australian Clinical Labs, Path Focus)
- Considerations for patients on obesity medication (American Association of Clinical Endocrinology)
This article is for general education and does not replace a consultation. Medicines and treatments are prescribed only after a doctor's assessment. Last reviewed 25 October 2026.