The most common side effects men experience when hCG injections are used include:
- growth of male breasts (gynecomastia)
- pain, redness, and swelling at the injection site
- stomach pain
- nausea
- vomiting
from:
and from here:
HCG may also result in an abnormal enlargement of breasts in men, a condition called gynaecomastia. According to NDARC, this happens because use of HCG encourages the body to convert testosterone to estrogen, a female hormone that supports the development and maintenance of female sexual characteristics. In an attempt to prevent gynaecomastia, some users of HCG often take it in combination with an estrogen blocker.