There is only one form of poisoning that that it is possible for the owner to address without veterinary help and that is the organic kind.
The symptoms of muscle tremor and an inability of the guinea pig to hold it's head up, which tends to keep slipping away to one side.
More often than not it occurs when the guinea pig have been given freedom to roam in the garden for the first time, and it more likely to be seen in younger animals. I think this is because the older animals have 'wiser' appetites, so to speak, while the younger ones take the attitude, 'It's green so let's eat it!.'
As guinea pigs cannot vomit the use of an emetic is out of the question. What ever goes down the throat has to come out of the back end and the hastier this is done in the case of anything toxic, the better.
Crush a 100mg charcaol tablet, mix with a small amount of water and syringe into the mouth. In the two cases I dealt with, though the animals were traumatised, both were able to swallow the medicine. This will absorb what is n the gut, including the poison, hopefully.
Wait for half an hour and then give 1.05 liquid parafin by syringe. Keep the animal warm and n the dark by putting it into box with plenty of hay in it. Make sure there is also food and water in there.
Providing you have caught the guinea pig early enough, within twelve hours you will have a whole heap of dropping and a healthy guinea pig. I haven't lost one yet, but in both cases the symptoms were noticed quickly.
A subcutaneous injection of vitamin B is recommended and plenty of rehydration fluid.