A prodrome is an early stage of a condition that might have different symptoms than the full-blown version. In psychiatry, the prodrome of schizophrenia is the few-months-to-few-years period when a person is just starting to develop schizophrenia and is acting a little bit strange while still having some insight into their condition.
There's a big push to treat schizophrenia prodrome as a critical period for intervention. Multiple studies have suggested that even though schizophrenia itself is a permanent condition which can be controlled but never cured, treating the prodrome aggressively enough can prevent full schizophrenia from ever developing at all. Advocates of this view compare it to detecting early-stage cancers, or getting prompt treatment for a developing stroke, or any of the million other examples from medicine of how you can get much better results by catching a disease very early before it has time to do damage.
These models conceptualize psychosis as "toxic" – not just unpleasant in and of itself, but damaging the brain while it's happening. They focus on a statistic called Duration of Untreated Psychosis. The longer the DUP, the more chance psychosis has had to damage the patient before the fire gets put out and further damage is prevented. Under this model it's vitally important to put people who seem to be getting a little bit schizophrenic on medications as soon as possible.
There has been a lot of work on this theory, but not a lot of light has been shed. Observational studies testing whether duration of untreated psychosis correlates with poor outcome mostly find it does a little bit, but there's a lot of potential confounding – maybe lower-class uneducated people take longer to see a psychiatrist, or maybe people who are especially psychotic are especially bad at recognizing they are psychotic. The relevant studies try their hardest to control for these factors, but remember that this is harder than you think. The randomized controlled trials of what happens if you intervene earlier in psychosis tend to do very badly and rarely show any benefit, but randomly intervening earlier in psychosis is hard, especially if you also need an ethics board's permission to keep a control group of other people who you are not going to intervene early on. Overall I could go either way on this.