Peptide therapy is considered to be a very safe form of treatment, with minimal side effects. The most common side effect is developing flu-like symptoms after receiving the injection. This is said to occur in a small percentage of peptide therapy patients and tends to be mild, as well as transient. A serious adverse effect of peptide therapy is an allergic reaction, although this is a fairly rare occurrence. Speak with a medical expert to determine whether you should receive peptide therapy.