You can also buy Oxbow Vitamin C supplements that you can hand feed to them, crush over their veggies, or crush over their pellets, if you are worried that they are not getting enough vitamin C. I feed those to may pigs, just because only Ro Dah likes fruits, the rest of them don't so I will hand feed them the tablets to make sure they get enough vitamin C. As said above, just make sure you don't put the drops in their water because one: They make the water taste bad for piggies, and some won't drink it two: It won't even help your piggies, because vitamin C degrades fast in water, sunlight, and air. So by the time they take a drink all there will be is just some bad tasting water. I would also look into finding a new vet, if yours gave you these drops, because most good guinea pig vets would say not to put drops in the water. So this might lead to bigger problems if your vet doesn't know much about guinea pig care.