Weight gain and loss are uncommon symptoms of taking meloxicam. But fluid retention is, in fact, a common side effect, reported in 0.6% to 4.5% of people taking it. Fluid retention is not treated can lead to cardiovascular problems and further lead to congestive heart failure. One thing that happens with fluid retention is an involuntary rise in body weight. So, if you see some weight gain, it could affect fluid retention. Visit your doctor immediately.