Trazodone 100 mg is primarily prescribed to treat depression, its only FDA-approved use. However, it is one of the most commonly prescribed medications for insomnia, with doses between 25 and 100 mg widely used off-label to help people fall and stay asleep. Whether your doctor prescribed it for mood, sleep, or both, the 100 mg dose sits at an important crossover point between these two uses.
Depression: The Approved Use
Trazodone works by increasing serotonin activity in the brain. It does this in two ways: it blocks the reabsorption of serotonin (so more stays available between nerve cells) and it blocks certain serotonin receptors that can interfere with mood regulation. This dual action is what sets it apart from more common antidepressants like SSRIs.
For depression, 100 mg is typically a starting-range dose. The usual beginning dose is 150 mg per day, split into smaller doses taken throughout the day, with a maximum of 400 mg daily. So if you’ve been prescribed 100 mg specifically for depression, your prescriber may plan to adjust upward over time depending on how you respond. The antidepressant effects take time to build. You may notice some changes in the first one to two weeks, but the full benefit generally takes four to six weeks.
Insomnia: The Most Common Off-Label Use
Despite never receiving FDA approval for sleep, trazodone at low doses (25 to 100 mg) has become a go-to option for insomnia. The sleep-promoting effect comes from the same receptor-blocking action that contributes to its antidepressant properties, particularly its ability to block histamine and certain brain receptors involved in wakefulness. At these lower doses, trazodone induces and maintains sleep without causing next-day grogginess or building tolerance, largely because the drug clears the body relatively quickly, with a half-life of three to six hours.
A six-week trial of 75 participants compared trazodone doses of 50, 75, and 100 mg per day for sleep. All three doses improved sleep, but 100 mg produced the best results. Other studies found that a single 100 mg dose increased deep slow-wave sleep (the most restorative phase) and improved total sleep time. This makes 100 mg something of a sweet spot for sleep: effective, but still in the low-dose range where side effects tend to be minimal.
The sedating effect kicks in quickly. Most people feel sleepy within the first few days, which is why trazodone for insomnia is taken at bedtime rather than during the day. This fast onset for sleep contrasts sharply with the weeks-long wait for antidepressant benefits, which is worth knowing if your prescription is meant for mood rather than sleep.
How It Feels: Common Side Effects
The most frequently reported side effects of trazodone are drowsiness, dizziness, and dry mouth. At 100 mg or below, these tend to be mild. Studies of low-dose trazodone for insomnia in people without depression consistently show little to no adverse effects. Above 100 mg per day, drowsiness becomes more common and more noticeable, which is one reason the sleep dose is kept low.
Weight changes are possible but uncommon. In clinical trials, about 5% of people taking trazodone gained weight while 6% lost weight, making it essentially neutral. Compared to many other antidepressants, trazodone carries a lower risk of weight gain.
Priapism: A Rare but Serious Risk
One side effect that deserves specific mention is priapism, a prolonged, painful erection unrelated to sexual arousal. This is rare, occurring at a rate of about 1.5 cases per 100,000 person-years of use (slightly higher in men over 40). But it is a medical emergency. Untreated priapism can permanently damage erectile function. If this occurs, it requires immediate medical attention, and the medication will need to be stopped and replaced.
Interactions With Other Medications
Because trazodone increases serotonin levels, combining it with other serotonin-boosting medications raises the risk of serotonin syndrome, a potentially dangerous condition involving agitation, rapid heart rate, high blood pressure, and muscle rigidity. This includes other antidepressants (SSRIs, SNRIs, MAOIs), certain migraine medications, and the supplement St. John’s wort. If you take any of these, your prescriber needs to know before you start trazodone.
What Happens When You Stop
Trazodone should not be stopped abruptly. Even at 100 mg, stopping suddenly can trigger withdrawal symptoms including low mood, trouble sleeping, and panicky feelings. These can mimic the very symptoms the medication was treating, which makes it hard to tell whether the original problem is returning or you’re experiencing withdrawal. The standard approach is tapering: gradually reducing the dose over weeks or months. How quickly you can taper depends on how long you’ve been taking it. People who have only used trazodone briefly may only need a couple of step-downs, while longer-term users generally need a slower, more gradual reduction.