What can happen if you overdose on antibiotics tablets?

It depends. There are as many answers to this question as there are antibiotics. Many are not particularly harmful if you get a slightly higher-than-recommended amount. However, they can cause serious problems. They can affect your liver or kidneys, or interfere with other medicines, for example. An excellent resource for overdose questions of any kind is the poison control center at 1(800)222-1222.