No. I have never heard of any harmful effects of meditation, while a large body of research has demonstrated a wide range of benefits for physical and mental health. However, I have observed that if you meditate for too long seated in a lotus or semi-lotus position it can cause some temporary knee discomfort!
Not harmful, but. Meditation itself is not harmful, but certain people might find it distressing. People who have untreated trauma may find the emotions that can arise during silence, painful. Trauma needs addressing, for healing. Those who have impaired concentration due to severe depression or psychotic illness, or active suicidal ideation may not benefit from meditation, and need definitive treatment first.