Short answer: adult guinea pigs need about 10–25 mg of vitamin C per kilogram of body weight every day — roughly 7–30 mg for a typical adult — and 30 mg/kg or more when growing, pregnant, nursing or ill, according to the Merck Veterinary Manual. Fresh fortified pellets plus daily vitamin-C-rich vegetables such as bell peppers usually cover it.
Most small pets can make their own vitamin C, but guinea pigs — like humans — cannot, which makes vitamin C one of the few nutrients in small-pet care where getting the amount right is about preventing a specific, well-documented deficiency disease.
Why Do Guinea Pigs Need Dietary Vitamin C Specifically?
According to the Merck Veterinary Manual, guinea pigs “are incapable of endogenous synthesis because they have a mutated gene for L-gulonolactone oxidase” — the enzyme most mammals use to make vitamin C. Every bit of vitamin C a guinea pig gets has to come from its diet. Without enough, guinea pigs develop scurvy, a deficiency disease that affects connective tissue, joints, gums and wound healing.
How Much Vitamin C Do Guinea Pigs Actually Need?
Merck gives 10–25 mg per kg of body weight daily for healthy adults, and 30 mg/kg or more for growing, pregnant, nursing or ill guinea pigs. Its pet owner edition gives a floor of at least 10 mg/kg a day. VCA Animal Hospitals expresses it as a total of 10–50 mg a day. Because the requirement scales with weight, it helps to weigh your guinea pig. VCA gives typical adult weights of 700–900 g for females and 900–1,200 g for males:
| Guinea pig weight | Healthy adult (10–25 mg/kg/day) | Growing, pregnant, nursing or ill (30+ mg/kg/day) |
|---|---|---|
| 700 g | 7–17.5 mg | 21 mg or more |
| 900 g | 9–22.5 mg | 27 mg or more |
| 1,200 g | 12–30 mg | 36 mg or more |
These are reference ranges, not a prescription. If your guinea pig is pregnant, recovering from illness or not eating well, ask an exotics-experienced vet how to meet its needs.
What Are the Best Sources of Vitamin C for Guinea Pigs?
- Fresh guinea pig pellets: the foundation. Many use a stabilized form of vitamin C that resists heat and light better, but it still degrades over time — VCA advises using or replacing pellets within 90 days of the manufacture date. Never substitute rabbit pellets; Merck notes they lack enough vitamin C, and a history of rabbit pellets or old pellets is a classic scurvy risk factor
- Bell peppers: red and green bell peppers top Merck’s list of high-vitamin-C vegetables, and the RSPCA lists bell peppers as a daily food
- Tomatoes and leafy greens: Merck also lists tomatoes, kale, parsley, beet greens and spinach as high in vitamin C. However, its pet owner guide advises limiting high-calcium greens like parsley, kale and spinach because of bladder-stone risk, so rotate them rather than feeding large amounts daily
- Skip citrus: the RSPCA lists citrus fruits among foods guinea pigs should avoid
- Supplements only on vet advice: VCA says guinea pigs on a good diet usually don’t need one, and Merck says adding vitamin C to drinking water is not recommended
What Happens If a Guinea Pig Doesn’t Get Enough?
Deficiency causes scurvy. Merck lists signs including reluctance to eat or difficulty picking up food, a rough coat, lameness or weakness in the legs, swollen joints, generalized pain and delayed wound healing. VCA adds bleeding or ulcers on the gums or skin, and notes that vitamin C deficiency can contribute to dental disease. Growing, pregnant, nursing and sick guinea pigs can show signs faster than healthy adults.
Scurvy signs overlap with other problems, so don’t guess — any of these, especially reluctance to move or not eating, warrants a vet visit. A guinea pig that has gone quiet and is hiding all the time or showing other signs of illness needs checking promptly.
How Can You Make Sure Your Guinea Pig Is Getting Enough?
- Check the manufacture date on pellets and use them within 90 days (VCA); buy smaller bags if you have only one or two guinea pigs
- Store pellets in a cool, dark, airtight container — the RSPCA notes vitamin C is destroyed over time, and faster with exposure to air
- Feed fresh vitamin-C-rich vegetables every day as a core part of the diet, not an occasional treat
- Weigh your guinea pig regularly so you know roughly how much it needs
- Tell your vet if your guinea pig is pregnant, ill or eating less, since its requirement rises and intake often falls at the same time
- Arrange daily fresh food when you travel — see how long guinea pigs can be left alone
For the rest of the menu — hay, pellet portions and foods to avoid — see our guinea pig and hamster feeding guide. Because guinea pigs can’t make up for a shortfall on their own, consistent daily vitamin C is one of the most important basics to get right in their care.
This article is for informational purposes only and does not replace guidance from your veterinarian.
Sources
- Merck Veterinary Manual — Housing and Nutrition of Guinea Pigs (Miranda J. Sadar, DVM), May 2026
- Merck Veterinary Manual — Noninfectious Diseases of Guinea Pigs, May 2026
- Merck Veterinary Manual (Pet Owner Version) — Nutritional Problems of Guinea Pigs, October 2025
- Merck Veterinary Manual (Pet Owner Version) — Diet for a Guinea Pig, October 2025
- VCA Animal Hospitals — Feeding Guinea Pigs, August 2026
- VCA Animal Hospitals — Health Problems in Guinea Pigs, April 2023
- VCA Animal Hospitals — Guinea Pigs: Owning, March 2019
- RSPCA — Guinea pig diet
