Already stated in the notes:
"Serum Injection is similar to mutate, in that it can cause negative side effects, such as poison, aflatoxin or death. However, it is probably more likely to cause the addition of adrenaline, momentum, vampire or an increase in attack power, hit points, or both. There is also a decent chance at causing a mutation. The exact likelihoods of each potential outcome are impossible to know at this point.
Serum Dose is similar to improve, with the chance to have a negative outcome being infinitesimally small. It is far more likely to generate one or two of the positive potential effects of the injection."