Doxycycline can help joint pain and inflammation from other causes.
This medication has been shown to have anti-inflammatory properties.
In cats, doxycycline can cause damage to the esophagus and has to be given orally in a liquid form, followed by a syringe of water.
Many cats don't cooperate well for this. Treatment with doxycycline in cats has to be carefully considered by your veterinarian.