Citalopram can cause following main side effects;
1) Central nervous system: epilepsy, tremors, restlessness, imbalance, in coordination, confusion, agitation, sweating, sleep problems, ringing in ears, etc.
2) Cardiovascular: fast heart beats,
3) Gastrointestinal tract: nausea, bloatiness, gas formation, upset stomach, loss of appetite
3) Endocrinal and sexual; weight loss or gain, impotence, less sex drive, orgasm problems etc.
4) Urinary tract: increased urination etc.
These are the main side effects. But individual people can have other side effects too. Read the link;
Your follow up questions are welcome.