**Core Concept**
Glucocorticoids are a class of steroid hormones that are widely used as immunosuppressants to prevent organ rejection in transplant patients and to treat autoimmune diseases. Long-term use of glucocorticoids is associated with various side effects, including bone loss and osteoporosis.

**Why the Correct Answer is Right**
Glucocorticoids exert their immunosuppressive effects by inhibiting the expression of inflammatory genes and suppressing the activity of immune cells, such as T lymphocytes and macrophages. However, one of the major side effects of chronic glucocorticoid use is the suppression of osteoblast activity and the enhancement of osteoclast activity, leading to a net loss of bone mass and an increased risk of osteoporosis. This is due to the inhibition of glucocorticoid-induced osteoblast differentiation and the activation of the RANK/RANKL/OPG pathway, which promotes osteoclast formation and activity.

**Why Each Wrong Option is Incorrect**
**Option A:** Cyclosporine is an immunosuppressant that inhibits calcineurin, which is involved in T-cell activation, but it is not typically associated with osteoporosis as a side effect.
**Option B:** Tacrolimus is another calcineurin inhibitor that is used to prevent organ rejection, but it is not commonly linked with osteoporosis.
**Option C:** Mycophenolate mofetil is an antimetabolite that inhibits lymphocyte proliferation, but it is not typically associated with osteoporosis as a side effect.

**Clinical Pearl / High-Yield Fact**
Glucocorticoids can cause osteoporosis by suppressing osteoblast activity and enhancing osteoclast activity, leading to a net loss of bone mass. This side effect is particularly relevant in patients who require long-term glucocorticoid therapy, such as those with chronic autoimmune diseases or organ transplant recipients.

**Correct Answer: C. Glucocorticoids**