No, on the contrary donating blood increases testosterone levels in blood.
Testosterone actually decreases the level of the iron-regulatory hormone; hepcidin, allowing for more iron to be absorbed from foods. This is one of the reasons why men tend to have higher hemoglobin levels and larger blood volume than women do but over the time excessive amounts of iron in body can suppress the function of the hypothalamus, pituitary gland, and testicular leydig- and sertoli-cells, resulting in lowered testosterone levels. Donating blood reduces excess iron build in men and boost testosterone level in blood.
Sometimes people who donate blood notice a few minor side effects like weakness, nausea, light-headedness, dizziness, or fainting, but these symptoms usually go away quickly. These symptoms occur because the donor's body usually replaces the liquid part of blood (plasma) within 72 hours after giving blood. It generally takes about 4–8 weeks to regenerate the red blood cells lost during a blood donation.