Does taking cortisone for a long time weaken your bones?

Yes, that is correct: tablets or injections of corticosteroids (such as prednisone) demonstrably damage the bones with prolonged use. The loss is fastest in the first one to two years after starting, but bone density continues to decline after that as well. The risk of fractures due to osteoporosis increases, in both children and adults and also with repeated shorter courses.

The situation with inhaled medications (such as those used for asthma) is more nuanced. At low to moderate doses, no clear adverse effect on bone density has been demonstrated. At high or long-accumulated doses there are indications of a dose-dependent decline, but the studies partly contradict one another. The risk is in any case considerably smaller than with tablets or injections. In children who use high doses of inhaled medications, bone growth may decrease slightly; adequate calcium and vitamin D in the diet appears to limit this.

Fortunately, something can be done about it. People who use high doses of corticosteroids in tablet or injection form for a prolonged period can limit bone loss by starting preventively on medications that protect the bones, such as bisphosphonates or active vitamin D. In postmenopausal women, hormone therapy is sometimes also considered. Discuss this with your doctor as soon as a longer course is on the horizon, because starting before the loss occurs is more effective than intervening after the fact.

If you use only a low dose of inhaled medication for asthma, there is no reason for extra concern about your bones based on current knowledge. If you have been using high doses for years, it is worthwhile to have your doctor measure your bone density.