It's generally best to avoid alcohol while taking trazodone — the FDA medication guide flatly says "do not drink alcohol" until you've talked with your doctor, because the two are both sedating and combining them can deepen drowsiness, dizziness, and slowed breathing.
Trazodone is a sedating antidepressant and alcohol is a central-nervous-system (CNS) depressant, so their sedating effects stack — more intense drowsiness, dizziness, impaired thinking and coordination, and at the extreme, dangerously slowed breathing. The FDA-approved Medication Guide is explicit: "Do not drink alcohol or take other medicines that make you sleepy or dizzy while taking trazodone hydrochloride tablets until you talk with your healthcare provider." MedlinePlus stops slightly short of an absolute ban, telling patients to "ask your doctor about the safe use of alcoholic beverages" because "alcohol can make the side effects from trazodone worse." The professional prescribing label states that "trazodone may enhance the response to alcohol, barbiturates, and other CNS depressants," and — most seriously — its overdose section notes that "death from overdose has occurred in patients ingesting trazodone and other CNS depressant drugs concurrently," listing alcohol first. There is no source-stated safe amount and no safe waiting window, and NIH's NIAAA lists trazodone (Desyrel) among antidepressants that combine with alcohol to cause drowsiness, dizziness, and increased overdose risk.
Warning signs of too much CNS depression: heavy "can't fight it" drowsiness, marked dizziness or unsteadiness, confusion, fainting, and — most urgently — slow, shallow, or difficult breathing, or someone who can't be woken; that is a medical emergency, call 911 (or Poison Help, 1-800-222-1222). Do not drive or operate machinery until you know how the combination affects you — the FDA Medication Guide warns trazodone "can slow your thinking and motor skills," and alcohol makes that worse. Be most cautious (or avoid entirely) if you are older, take other sedating medicines (barbiturates, benzodiazepines, opioids, sleep aids, muscle relaxants), or have liver, kidney, heart (including long-QT or heart-rhythm history), or breathing problems. The sources give no specific number of hours, so there is no stated safe separation window — the honest guidance is to avoid alcohol rather than try to "space it out." Before drinking any alcohol on trazodone, ask your own doctor or pharmacist about your situation, and call promptly if you notice unusual sedation, breathing changes, fainting, or a fast or irregular heartbeat.
This is general reference, not medical advice, and not a guarantee of safety. Interactions depend on your doses, health conditions, and other medicines. Always confirm with your pharmacist or doctor before combining products, and follow the dosing on each label.