The lowest dose of trazodone commonly prescribed is 25 mg, typically taken at bedtime for sleep. The smallest manufactured tablet is 50 mg, but it comes scored down the middle so it can be split in half to create a 25 mg dose. This half-tablet starting point is especially common for older adults and for the drug’s most widespread use: treating insomnia.
Why the Lowest Prescribed Dose Differs From the Label
Trazodone was originally approved by the FDA as an antidepressant, and the official label recommends a starting dose of 150 mg per day in divided doses for depression. That’s the lowest FDA-approved dose for its on-label purpose. But in practice, the vast majority of trazodone prescriptions today are written off-label for insomnia, at doses far below what’s needed for depression. Doses of 25 to 50 mg at bedtime are standard starting points for sleep.
This isn’t a case of doctors going rogue. The gap between the labeled dose and the sleep dose exists because trazodone does fundamentally different things in your brain at different amounts.
How Dose Changes What the Drug Does
At a low dose like 50 mg, trazodone strongly blocks three types of receptors in the brain that promote wakefulness and arousal. A study from King’s College London estimated that at 50 mg, the drug blocks about 97% of one key serotonin receptor involved in sleep regulation, 88% of a noradrenaline receptor, and 84% of a histamine receptor. That triple blockade is what makes you drowsy.
What trazodone does not do well at 50 mg is act as an antidepressant. Its antidepressant effect depends on blocking the serotonin transporter, and at 50 mg the drug barely touches it. You need at least 150 mg daily before serotonin transporter blockade reaches roughly 90%, which is the threshold where antidepressant effects kick in. This is why the depression starting dose is three to six times higher than the sleep dose.
Starting Doses by Purpose
For insomnia, most prescribers start at 25 to 50 mg taken once at bedtime. If 25 mg isn’t enough, the dose can be increased in 25 mg increments. Sleep doses rarely exceed 100 mg.
For depression, the starting dose is 150 mg per day, split into two or three doses throughout the day. This can be gradually increased up to 400 mg per day for outpatients, though the extended-release version caps at 375 mg.
For older adults, regardless of the reason, the typical starting point is 25 to 50 mg at bedtime, with slower increases in 25 to 50 mg steps. This caution exists because trazodone can cause a drop in blood pressure when standing up, which happens in roughly 4 to 7% of users overall and poses a greater fall risk for older people.
How Quickly It Works
Trazodone reaches its peak blood levels about one hour after taking it on an empty stomach, or about two hours if you take it with food. This is why it’s typically taken 30 to 60 minutes before bed when used for sleep. Even at a single 25 mg dose, the drug reaches meaningful blood concentrations relatively quickly. Taking it with food slows absorption but can also reduce the chance of nausea.
Side Effects at Low Doses
Most side effect data comes from studies using the higher antidepressant doses, so the exact rates at 25 mg aren’t well documented. At full doses, the most common side effects are drowsiness (affecting up to 41% of users), dry mouth (up to 34%), dizziness or lightheadedness (up to 28%), and headache (up to 20%). These effects are generally milder and less frequent at lower doses, though drowsiness is essentially the intended effect when the drug is prescribed for sleep.
The most common complaint at low doses is next-day grogginess, a hangover-like feeling that usually improves as your body adjusts over a few days. If you’re splitting a 50 mg tablet to take 25 mg and still feeling groggy the next morning, that’s worth mentioning to your prescriber, as it may mean the drug is lingering in your system longer than ideal.
Tablet Sizes and Splitting
Trazodone immediate-release tablets come in 50 mg, 100 mg, 150 mg, and 300 mg strengths. The 50 mg tablet is the smallest available, and the FDA-approved label specifically notes it can be broken along its score line to create two 25 mg halves. There is no commercially manufactured 25 mg tablet, so splitting is the standard way to get that dose. A pill splitter gives cleaner, more even halves than breaking by hand.