I am a driver. I have been taking anti depressant medication for many years and am technically under the care of mental health services. From time to time I have to undergo additional work medicals. I have a clean safety record stretching back more than twenty years.
I find it hard to believe that there are not other drivers on anti depressant medication. If there are none, then either train drivers as a group must be remarkably resistant to depression, or given how common problems such as depression are, there are a lot of drivers trying to cope with mental health problems by themselves who are perhaps too worried to admit to it for fear of losing their jobs.
Please note that I did say "recruit". If you are an existing employee then a duty of care exists to properly assess the individual and ensure that the job is manageable.
For recruits the system, as designed, can pick and choose the best recruit, not only in terms of abilities but also that of health.
I am not saying that you cannot apply. Just pointing you in the direction that states that the medical standards are aware that anti-depressants can affect safety critical work and as a recruit they can ask that you be free from the medication and be generally well thereafter.
JetStream - epileptics are NOT fine to drive!
Anyway, good luck in your application but don't be surprised if they ask you to come back once you're free of the medication and review from the MH team or GP.