Depends on what you are spiking it with? If you are spiking a soda with alcohol the person gets drunk. But if you are talking about drugs it depends on the drug.
If you are asking about spiking a drink with a drug that makes the person unable to remember and become semi conscious I think you are talking about rohypnol. It is also known as the date rape drug, roofies, etc. This is a very dangerous drug and was originally used to sedate patients before a medical procedure. Is that what you wanted?