Antidepressants can sometimes cause a wide range of unpleasant side effects, including: 1  nausea. 2  increased appetite and weight gain. 3  loss of sexual desire and other sexual problems, such as erectile dysfunction and decreased orgasm.4  fatigue and drowsiness.5  insomnia. 6  dry mouth.7  blurred vision. 8  constipation.9  dizziness.ntidepressants can sometimes cause a wide range of unpleasant side effects, including: 1  nausea. 2  increased appetite and weight gain. 3  loss of sexual desire and other sexual problems, such as erectile dysfunction and decreased orgasm. 4  fatigue and drowsiness. 5  insomnia. 6  dry mouth. 7  blurred vision. 8  constipation. 9  dizziness.