Weight Loss Injections And Pregnancy: What You Need To Know About Contraception

Article Summary:

• Weight loss injections may be suitable for those living with obesity, as well as those with overweight and an obesity-related health condition.
• However, they can cause side effects which may delay or reduce absorption of oral medicines, including the contraceptive pill.
• Weight loss injections should not be taken during pregnancy, when trying to conceive or while breastfeeding, due to limited human safety data. Wait at least 2 months after treatment before trying to conceive, to allow for the ‘washout’ period.

Weight Loss Injections And Pregnancy: What You Need To Know About Contraception

If there's a chance you could become pregnant and you're considering weight loss treatment, it’s important to know how it might affect your fertility or interact with your current birth control method.

Whether you’re planning to have a family or want to avoid pregnancy, here's what you need to know about weight loss injections, pregnancy and contraception.

Weight management and fertility

Weight and fertility are closely connected. Being underweight or overweight can impact your chances of getting pregnant, so it follows that weight loss treatments may have implications for your reproductive health, too. [1] [2]

For instance, living with obesity (a body mass index (BMI) of 30 or higher) can impact fertility, but reaching a lower BMI may improve your chances of conceiving (we’ll explain how later). [3] [4]

However, weight loss injections do not act directly as fertility drugs, and should never be used in this way. In fact, Health Canada recommends that patients use contraception while taking weight loss injections. [5] [6]

It’s important to understand exactly why effective contraception matters while taking weight loss injections, and also how the treatment may interact with the birth control pill.

How do weight loss injections affect the pill?

While studies remain limited, the current evidence suggests that weight loss injections may affect the effectiveness of oral contraception. Here's how:

Slowing down digestion

One of the ways these medications work is by significantly slowing down the rate at which food leaves your stomach, helping you stay fuller for longer. [7] Although this supports appetite control, certain weight loss injections may also alter the way oral contraceptives are absorbed by your body. [8] This may make them less effective.

Fortunately, there’s no evidence that weight loss injections reduce the effectiveness of non-oral hormonal contraceptives. This means alternatives like the intrauterine device (IUD), implant, injection, patch, and vaginal ring remain safe options. Additional barrier contraceptives, like condoms, are also advised.

Whichever method you choose, always use a form of birth control while taking weight loss injections. This is because weight loss injections should not be used while pregnant.

Side effects that can impact pill absorption

Some of the more common side effects of weight loss injections (like diarrhea and vomiting) can also affect the efficacy of the birth control pill, just as a stomach bug would. If you experience either of these symptoms while taking weight loss injections, follow the missed pill guidance in your patient medication information leaflet or use a backup method to avoid unplanned pregnancy.

If you experience persistent vomiting or diarrhea, consider using a non-oral contraception method. Contact your physician to discuss your options.

Reducing obesity

When coupled with positive lifestyle changes (like a balanced diet, quality sleep and increased fitness), weight loss injections may help reduce body mass index. [9] This can improve insulin sensitivity and metabolic health. [10] [11] Weight loss may also restore regular ovulation and increase fertility, especially in people whose infertility is related to obesity or polycystic ovary syndrome (PCOS). [12]

Do weight loss injections interact with oral emergency contraception?

It’s not yet known what effect weight loss injections may have on oral emergency contraception, commonly known as the 'morning-after pill'. To be safe, the copper IUD is a recommended option as it can be fitted by a clinician up to 7 days after unprotected sex. [13]

Always tell your healthcare provider about any weight loss medication use if you’re seeking emergency contraceptives.

Weight loss injections and family planning

If you’re planning to get pregnant

Talk to your healthcare provider about your plans, and do not use weight loss medications while trying to conceive. This is because there's not enough human data on the risks of getting pregnant on weight loss injections. [5] [6]

It's recommended that you wait at least 2 months after your last dose before trying to get pregnant, depending on which treatment you're taking. [5] [6] This is known as the 'washout' period, where you make sure the medication is fully cleared from your system before trying to conceive. For more information, please refer to your patient medication information leaflet or speak to your physician.

If you suspect you are pregnant while on weight loss injections, stop the treatment and seek medical advice about next steps and monitoring.

If you’re using contraception to protect against pregnancy

As we've discussed, weight loss injections may reduce the effectiveness of oral contraceptives. It's strongly recommended that you use an additional barrier form of contraceptive like condoms, or switch to a non-oral hormonal method to stay protected.

Certain types of weight loss treatment may cause side effects. If you experience severe diarrhea that lasts for more than 24 hours, or vomiting within 3 hours while taking the oral contraceptive pill, you may need a repeat dose. Contact your physician or call 811 for medical advice if this occurs.

If you’re pregnant or breastfeeding

Weight loss injections should not be used during pregnancy. You also shouldn't use weight loss injections while breastfeeding, because we don't have enough long-term data to determine whether this poses a health risk to either parent or baby. [5] [6]

For further information, please speak to your healthcare provider.

Ready to start your weight loss journey? Check your eligibility and find out which treatment may be suitable for you with MedExpress.

References

1. Weight, fertility, and pregnancy | Office on Women’s Health [Internet]. OASH | Office on Women’s Health. 2021. Available from: https://womenshealth.gov/healthy-weight/weight-fertility-and-pregnancy
2. Belan M, Gélinas M, Carranza-Mamane B, Langlois MF, Morisset AS, Ruchat SM, et al. Protocol of the Fit-For-Fertility study: a multicentre randomised controlled trial assessing a lifestyle programme targeting women with obesity and infertility. BMJ Open. 2022 Apr;12(4):e061554.
3. Canada H. Canadian Guidelines for Body Weight Classification in Adults [Internet]. aem. 2003. Available from: https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/healthy-weights/canadian-guidelines-body-weight-classification-adults/questions-answers-public.html
4. Ozcan Dag Z, Dilbaz B. Impact of obesity on infertility in women. Journal of the Turkish German Gynecological Association [Internet]. 2015 Jun 4;16(2):111–7. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4456969/
5. Product Monograph Ozempic ® semaglutide injection [Internet]. [cited 2026 Apr 21]. Available from: https://pdf.hres.ca/dpd_pm/00084255.PDF
6. Wegovy ® (semaglutide injection) Product Monograph Unclassified / Non classifié Product Monograph Including Patient Medication Information PR WEGOVY ® semaglutide injection Solution for Subcutaneous Injection in a pre-filled pen Produced by recombinant DNA technology in Saccharomyces cerevisiae [Internet]. Available from: https://pdf.hres.ca/dpd_pm/00082777.PDF
7. Lu J, Liu P, Cai M, Lv T, Zhang M, Yin K, et al. Recent progress in the pharmacotherapy for obesity. European Journal of Pharmacology [Internet]. 2025 Jun 17;1002:177850. Available from: https://www.sciencedirect.com/science/article/pii/S0014299925006041
8. Kettner J, Donnelly E, Maes ML. Glucagon-like Peptide-1 Receptor Agonists and Reproductive Health: Current Evidence and Clinical Implications. Journal of Pharmacy Practice. 2025 Sep 4;
9. Wilding JPH, Batterham RL, Calanna S, Davies M, Van Gaal LF, Lingvay I, McGowan BM, Rosenstock J, Tran MTD, Wadden TA, Wharton S, Yokote K, Zeuthen N, Kushner RF; STEP 1 Study Group. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med. 2021 Mar 18;384(11):989-1002. doi: 10.1056/NEJMoa2032183. Epub 2021 Feb 10. PMID: 33567185.
10. Clamp LD, Hume DJ, Lambert EV, Kroff J. Enhanced insulin sensitivity in successful, long-term weight loss maintainers compared with matched controls with no weight loss history. Nutrition & Diabetes [Internet]. 2017 Jun;7(6):e282–2. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5519190/
11. Yashi K, Daley SF. Obesity and Type 2 Diabetes [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2023. Available from: https://www.ncbi.nlm.nih.gov/books/NBK592412
12. Balen AH, Dresner M, Scott EM, Drife JO. Should obese women with polycystic ovary syndrome receive treatment for infertility? BMJ. 2006 Feb 23;332(7539):434–5.
13. Copper IUD – Planned Parenthood Toronto [Internet]. Available from: https://ppt.on.ca/factsheets/copper-iud/