Not every medication that’s fine for a dog outside pregnancy is fine during it — some carry real risks to the developing puppies or to the bitch herself. This guide covers the categories to be aware of and the general principle to follow.
The most important first
- Always check with your vet before giving any medication, supplement, or parasite treatment during pregnancy.
- NSAIDs are generally avoided in pregnancy due to developmental risk to the puppies.
- Calcium supplementation during pregnancy is generally discouraged — it can contribute to eclampsia risk.
- Deworming in the second half of pregnancy is commonly recommended by veterinary parasite guidelines — your vet should choose the product and schedule.
- Do not vaccinate during pregnancy unless your vet advises it; bring vaccines up to date before breeding.
- Medication caution continues through lactation, since puppies receive whatever passes into the milk.
A note on day counts: day numbers in this article are approximate and counted from ovulation, the date progesterone testing pins down. The LH surge comes about two days before ovulation, so a count “from the LH surge” runs about two days higher. If you only know the mating dates, her true day of pregnancy may be several days earlier or later, so allow a margin either way. Deworming schedules in particular are often written as “day 40 of pregnancy” or “day 42 after ovulation”, so check which one your vet means.
The general principle
Most medications should be assumed unsafe until confirmed otherwise, rather than assumed safe by default — the consistent guidance across veterinary sources is to check with a vet before giving anything, including over-the-counter products, to a pregnant bitch. This applies to medications she may have taken safely before pregnancy too, since pregnancy itself changes what’s appropriate.
Categories generally avoided
NSAIDs (non-steroidal anti-inflammatory drugs) are generally avoided during pregnancy because of possible developmental effects on the puppies. Calcium supplements given during pregnancy are generally discouraged, somewhat counterintuitively — rather than preventing problems, they can contribute to eclampsia (dangerously low blood calcium) risk around whelping and lactation by disrupting the body’s normal calcium regulation. Certain sedatives and anesthetic agents used in veterinary settings also carry pregnancy-specific cautions, which is exactly why any planned veterinary procedure during pregnancy should be flagged as such in advance.
Some common antibiotics are not recommended in pregnancy. Doxycycline, often used for tick-borne diseases, is one example. Herbal and “natural” remedies have little safety data, and pain-management guidelines advise avoiding them. If your bitch needs treatment for any condition, tell every veterinarian, nurse and pharmacist involved that she is pregnant.
Categories generally considered safer, with guidance
Many heartworm preventives are approved for use in pregnant dogs, but many flea and tick products have never been tested in pregnancy. Before using any parasite product, check that its label covers pregnant and lactating bitches, and confirm with your veterinarian. Treatment she already receives for a diagnosed condition should be reviewed with your veterinarian, not stopped on your own. Local anesthetics are generally considered safe and are the preferred option where pain control is needed during pregnancy. None of this is a substitute for actually checking with your vet about your specific bitch and situation — it’s context for that conversation, not a replacement for it.
In practice
A breeder gives their pregnant bitch a joint supplement containing added calcium, reasoning that “more calcium can only help” ahead of a demanding lactation period. Understanding that calcium supplementation during pregnancy can actually increase eclampsia risk, rather than prevent it, reframes a well-intentioned choice as one worth checking with a vet first, rather than assuming based on general nutrition logic.
(Illustrative, composite scenario.)
Deworming: a case where treatment is proactively recommended
Deworming during the second half of pregnancy is a notable exception to “avoid medication where possible”. Roundworm larvae lie dormant in the bitch’s tissues and wake up late in pregnancy. They then pass to the puppies through the placenta and later through her milk. Veterinary parasite guidelines therefore recommend treating the pregnant bitch, usually starting around day 40 of pregnancy and often continuing into early lactation. These protocols are off-label, and they vary, so your veterinarian should choose the product and schedule. Avoid deworming in early pregnancy unless your veterinarian advises it. This is worth discussing with your vet as part of pre-whelping planning, since it’s an example of a medication that’s actively protective in pregnancy, not just cautiously tolerated.
Vaccinations
Vaccinations should be brought up to date before breeding, ideally at least a month before she is mated, rather than during pregnancy. Modified-live vaccines given to a pregnant bitch carry a risk that the weakened virus reaches the puppies. If she is due a booster while pregnant, discuss timing with your veterinarian. In some countries, including much of Europe, a canine herpesvirus vaccine is licensed specifically for use during pregnancy to help protect newborn puppies; it is not available in the US. Ask your veterinarian what is available where you live.
Infection risk factors
Canine herpesvirus and Brucella canis can both cause pregnancy loss. The main protection against herpesvirus is keeping her away from dogs outside her household for the last three weeks of pregnancy and the first three weeks after whelping — see exercise, environment and daily life. If a pregnancy is lost, ask your veterinarian about testing; see what’s normal and what’s not.
When to call your vet
- Before giving any medication, supplement, flea, tick or worming product — including ones she has had before.
- She has been given a medication or supplement during pregnancy without checking — call to ask whether it matters.
- She needs treatment, a vaccine or a procedure for any reason — tell the clinic she is pregnant before anything is given.
- Panting, trembling, stiffness or restlessness in late pregnancy can be early eclampsia — call immediately.
- Her temperature rises above 103 °F (39.5 °C), or she has a bloody, foul-smelling, green or black discharge.
- If in doubt, call — your vet would rather hear from you early.
Work on it
A few minutes here will teach you more than re-reading the article.
Ask yourself
- Do I check with my vet before giving any medication or supplement during this pregnancy, even ones I’ve used before?
- Am I clear on why calcium supplementation during pregnancy isn’t automatically a good idea?
- Have I discussed a deworming protocol for the second half of pregnancy with my vet, and are her vaccinations up to date?
Find out & check
- Find out which of her current medications or supplements, if any, need review now that she’s pregnant.
- Check with your vet about a deworming protocol timed to the final weeks of this pregnancy.
Do one thing
- List every medication, supplement and parasite treatment she’s currently on, and run the list past your vet.
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Sources & further reading
- WSAVA Global Pain Council — Analgesia in Pregnant or Lactating Patients. wsava.org (PDF)
- Merck Veterinary Manual (J.A. Hall) — Puerperal Hypocalcemia in Small Animals. merckvetmanual.com
- Companion Animal Parasite Council — Ascarid Guidelines. capcvet.org
- American Kennel Club (Kolster, DVM, DACT) — The Importance of Preventative Health Care in Bitches and Puppies. akc.org
- Colorado State University Veterinary Teaching Hospital — Pregnancy and Whelping for Dogs. csuveterinaryhealth.org
- WSAVA Vaccination Guidelines Group (Squires et al., JSAP 2024) — 2024 Guidelines for the Vaccination of Dogs and Cats. wsava.org (PDF)
- Merck Veterinary Manual — Canine Herpesvirus Infection. merckvetmanual.com
- Dogs Victoria (ANKC member body, Australia) — Caring for Your Pregnant Bitch (fact sheet B16). dogsvictoria.org.au (PDF)
Where evidence is limited, recommendations rest on established practice and expert judgment, and may be updated as knowledge develops. This is general information, not a substitute for veterinary advice about a specific medication or supplement.
Next steps
- Read next: Preparing for whelping: the final two weeks.
- Related: The pregnant bitch’s health: what’s normal and what’s not.
- Return to the area hub: Pregnancy: managing the pregnant bitch week by week.