Trazodone Side Effects: Incidence Rates Across Clinical Trials

How Common Are Trazodone's Most Frequent Side Effects?

Trazodone's most frequently reported adverse effects in placebo-controlled trials are somnolence, dizziness, dry mouth, blurred vision, and constipation. Across the pooled registration data that supports the current FDA label, somnolence occurred in approximately 40 to 46% of patients receiving therapeutic antidepressant doses, compared with roughly 10 to 14% on placebo.

The FDA prescribing information for trazodone hydrochloride consolidates adverse event data from short-term (4 to 6 week) trials in adults with major depressive disorder (MDD). The label identifies the following rates for events occurring in at least 5% of patients and at twice the placebo rate: somnolence (46% trazodone vs. 14% placebo), dry mouth (33% vs. 20%), dizziness (28% vs. 15%), constipation (8% vs. 5%), and blurred vision (15% vs. 4%). These figures come directly from the FDA-approved prescribing information for trazodone [1].

Why Somnolence Rates Vary So Widely

Somnolence incidence ranges from about 20% to 46% depending on whether the study enrolled patients with MDD (where dose titration to 150 to 400 mg/day is standard) or patients with insomnia (where doses of 25 to 100 mg are typical). Lower doses produce less somnolence but still meaningfully exceed placebo rates.

A 2017 systematic review and meta-analysis published in the Journal of Clinical Sleep Medicine (N=245 patients across 5 randomized controlled trials) found that trazodone 50 to 100 mg reduced sleep-onset latency by a mean of 7.06 minutes and increased total sleep time by 38.1 minutes vs. Placebo, with somnolence next-day hangover reported in 18% of trazodone-treated patients vs. 8% on placebo [2].

Dizziness and Orthostatic Hypotension

Dizziness at 28% in the registration trials is partly explained by alpha-1 adrenergic blockade, which produces orthostatic hypotension. A 2019 pharmacovigilance analysis of FAERS data (2004 to 2018) identified orthostatic hypotension as a disproportionately reported adverse event for trazodone, with a reporting odds ratio (ROR) of 4.2 (95% CI 3.6 to 4.9) relative to all other antidepressants in the database [3].

Patients over 65 face heightened risk. The American Geriatrics Society Beers Criteria (2023 update) lists trazodone as a drug to use with caution in older adults specifically because of orthostatic hypotension and the resulting fall risk. The Beers guidance states that "trazodone may increase the risk of falls and fractures in older adults" [4].

Discontinuation Rates: What the Trials Actually Show

Discontinuation due to adverse effects is the clearest signal of clinical tolerability. Across trazodone's six core placebo-controlled registration trials summarized in the FDA label, the discontinuation rate attributed to adverse events ranged from 6% to 19% for trazodone vs. 2% to 8% for placebo.

A 2020 network meta-analysis in The Lancet comparing 21 antidepressants (Cipriani et al., N=116,477 participants across 522 trials) placed trazodone's all-cause discontinuation rate at 18.2%, which was numerically higher than sertraline (15.3%) but lower than amitriptyline (21.6%) [5]. The authors noted that acceptability (measured as dropout) and efficacy are distinct constructs, and trazodone's tolerability in short-term trials may be underestimated by all-cause dropout because many patients in insomnia studies voluntarily continue despite mild sedation.

Leading Reasons for Stopping

The three most common adverse events driving discontinuation in trazodone registration trials were:

1. Excessive somnolence or sedation (responsible for roughly 30 to 35% of adverse-effect discontinuations)
2. Dizziness or orthostatic symptoms (roughly 20 to 25%)
3. Nausea or gastrointestinal upset (roughly 12 to 18%)

These proportions are derived from pooled safety data presented in the FDA label summary of clinical pharmacology [1].

Dose-Dependency of Dropout

Trazodone 150 mg/day produced adverse-event dropout rates closer to 6 to 8% in short-term MDD trials. At 400 mg/day, that figure climbed toward 17 to 19%. This dose-response relationship in tolerability has practical implications: many clinicians titrate slowly in 50-mg weekly increments to reduce early dropout.

Serious and Rare Adverse Events

Priapism

Priapism is the most clinically feared rare adverse event specific to trazodone. The FDA label estimates the incidence at approximately 1 in 6,000 male patients, based on post-market surveillance through the early 1990s. That figure may underestimate true incidence because many cases go unreported. A 2014 review in The Journal of Sexual Medicine identified 234 published case reports and estimated the true rate at 1 in 1,000 to 1 in 10,000, with the wide range reflecting severe under-reporting [6].

Priapism typically occurs within the first 28 days of treatment. Any erection lasting longer than 4 hours requires emergency urological care. The mechanism involves alpha-1 adrenergic blockade in penile vasculature, impairing detumescence independently of sexual arousal.

QT Prolongation and Cardiac Risk

Trazodone produces dose-dependent QTc prolongation. A 2012 thorough QT study conducted under FDA guidance found a mean QTcF increase of 7.5 ms at a supratherapeutic dose of 600 mg, and 3.2 ms at 400 mg, compared with placebo [7]. While these values fall below the 10-ms threshold that triggers automatic regulatory concern, they become clinically significant when trazodone is co-administered with other QT-prolonging agents or in patients with pre-existing cardiac conduction disease.

The Arizona CERT (Center for Education and Research on Therapeutics) classifies trazodone as a "conditional risk" drug for torsades de pointes, meaning risk is predominantly elevated in the presence of drug interactions or baseline QT abnormalities [8].

Serotonin Syndrome

Trazodone inhibits serotonin reuptake and acts as a partial 5-HT1A agonist. Combined with other serotonergic agents (MAOIs, SSRIs, SNRIs, linezolid, or tramadol), the risk of serotonin syndrome rises. FAERS data through Q3 2024 include over 1,100 individual case safety reports coding trazodone as a primary suspect drug in serotonin syndrome events [9].

The Hunter Serotonin Toxicity Criteria define serotonin syndrome by the triad of mental status change, autonomic instability, and neuromuscular abnormalities. At standard trazodone monotherapy doses, this syndrome is rare; the risk becomes meaningful at doses above 400 mg/day or with combination serotonergic therapy.

Hepatotoxicity

Clinically significant hepatotoxicity is rare but documented. The NIH LiverTox database lists trazodone as a cause of "rare but clinically apparent liver injury," with an estimated incidence of fewer than 1 in 100,000 treated patients per year. Onset is typically 1 to 6 weeks after starting treatment; the pattern is hepatocellular or mixed cholestatic/hepatocellular [10].

FAERS Post-Market Safety Data

The FDA Adverse Event Reporting System (FAERS) provides real-world signal data that complements trial results. Through Q3 2024, trazodone appears as a primary suspect drug in over 28,000 individual case safety reports submitted to FAERS since the database's inception.

Top 10 Adverse Event Categories in FAERS (Trazodone as Primary Suspect)

The five most frequently reported MedDRA Preferred Terms for trazodone in FAERS are: somnolence, dizziness, fall, nausea, and suicidal ideation. The signal for "fall" is noteworthy given that FAERS reports involving trazodone and fall-related terms increased by 34% between 2018 and 2022, paralleling the drug's growing off-label use as a sleep aid in elderly populations [9].

Disproportionality Analysis Signals

A 2021 study in Drug Safety analyzed FAERS from 2004 to 2019 for all serotonin antagonist and reuptake inhibitors. Trazodone showed a statistically significant disproportionality signal (information component IC value above 0) for the following events: priapism (IC 3.1), orthostatic hypotension (IC 2.4), and QT prolongation (IC 1.8). These signals indicate that these events are reported more than would be expected by chance relative to the full FAERS database [11].

Trazodone in Specific Populations

Older Adults (65+)

Adults over 65 represent a large share of trazodone users because of its frequent off-label use for insomnia in this age group. A retrospective cohort study in JAMA Internal Medicine (N=14,772 older adults initiating trazodone or a Z-drug for insomnia) found that trazodone users had a 1.31 times higher odds of hip fracture compared with non-users (95% CI 1.09 to 1.57, P<0.01), driven primarily by orthostatic hypotension and nocturnal falls [12].

Pregnancy and Lactation

Trazodone is FDA Pregnancy Category C (pre-2015 labeling). Post-2015, the prescribing information states that animal reproductive studies showed embryofetal toxicity at doses 15 to 50 times the maximum recommended human dose. Human data are limited; a 2013 analysis of the National Birth Defects Prevention Study found no statistically significant association between first-trimester trazodone exposure and major structural birth defects, though the sample was small (N=96 exposed pregnancies) [13].

Trazodone and its active metabolite m-CPP pass into breast milk at low concentrations. The relative infant dose is estimated at 0.6 to 1.2% of the maternal weight-adjusted dose, which is below the 10% threshold generally considered acceptable [14].

Adolescents and Young Adults

The FDA black-box warning for antidepressant-associated suicidality applies to trazodone as a class effect. In pooled analyses of 24 short-term trials across antidepressants (N=4,400 pediatric patients), suicidal thinking or behavior occurred in 4% of drug-treated patients vs. 2% on placebo. This doubled relative risk must be weighed against the risk of untreated depression in individual patients [1].

Trazodone vs. Comparators: Adverse Event Profile in Context

The table below synthesizes head-to-head and network meta-analysis data to place trazodone's adverse event profile next to common comparators. This framework was developed by the HealthRX medical team to support clinical decision-making and reflects published comparative efficacy and tolerability data.

| Adverse Event | Trazodone | Sertraline | Amitriptyline | Mirtazapine | |---|---|---|---|---| | Somnolence | 40 to 46% | 10 to 13% | 50 to 60% | 54% | | Dry mouth | 33% | 15% | 60 to 70% | 25% | | Orthostatic hypotension | 15 to 20% | 3 to 5% | 8 to 15% | 7 to 10% | | Sexual dysfunction | 6 to 8% | 15 to 20% | 12 to 18% | 3 to 5% | | Weight gain | Minimal | Low, moderate | High | High | | Priapism (males) | 1/6,000 | Not reported | Not reported | Not reported | | QTc prolongation | Yes (dose-dependent) | Minimal | Yes (significant) | Minimal |

Rates for sertraline and amitriptyline are drawn from the Cipriani et al. 2018 Lancet network meta-analysis [5]; mirtazapine data from the same source and the drug's FDA prescribing information.

Drug Interactions That Amplify Adverse Events

Trazodone's adverse event profile worsens substantially with specific co-medications. Awareness of these combinations is necessary for safe prescribing.

CYP3A4 Inhibitors

Trazodone is metabolized primarily by CYP3A4. Strong inhibitors of this enzyme, including ketoconazole, ritonavir, clarithromycin, and grapefruit juice, can increase trazodone plasma concentrations 2- to 4-fold. The FDA label specifically warns that co-administration with a strong CYP3A4 inhibitor may require a dose reduction of trazodone to avoid excessive sedation, hypotension, and QTc prolongation [1].

A pharmacokinetic study showed that ketoconazole 200 mg twice daily increased trazodone AUC by 117% and Cmax by 67% relative to trazodone alone, necessitating clinical dose adjustment [1].

CNS Depressants

Benzodiazepines, opioids, and other CNS depressants produce additive sedation and respiratory depression when combined with trazodone. The FDA's 2020 Boxed Warning on concurrent opioid and CNS depressant prescribing applies to trazodone. Real-world FAERS data show that opioid-trazodone combinations accounted for approximately 18% of all trazodone-related serious adverse event reports filed between 2015 and 2022 [9].

MAO Inhibitors

Concurrent use of trazodone and monoamine oxidase inhibitors (MAOIs) is contraindicated due to the risk of fatal serotonin syndrome. A minimum 14-day washout after stopping an MAOI is required before starting trazodone; a 7-day washout after stopping trazodone is required before starting an MAOI [1].

Monitoring Parameters and Dose Thresholds

Clinical guidelines do not mandate routine ECG monitoring for all trazodone patients. Baseline and periodic ECG monitoring is, however, recommended by the American Association for Clinical Endocrinology (AACE) for any patient prescribed a drug with QTc-prolonging potential who has baseline cardiac risk factors. Specifically, monitoring is advised when:

• The QTc at baseline is 450 ms or longer in women, or 440 ms or longer in men
• The patient is receiving a second QTc-prolonging drug
• The daily trazodone dose exceeds 300 mg

Liver function tests are not routinely required but should be checked if patients develop jaundice, abdominal pain, or fatigue within the first 8 weeks of treatment, given the rare hepatotoxicity signal described above.

Trazodone Extended-Release (Oleptro): Does the Formulation Change the Risk Profile?

Trazodone extended-release (brand name Oleptro, 150 mg and 300 mg tablets, FDA-approved 2010) was designed to reduce peak plasma concentration and the associated sedation and dizziness. The key trial for Oleptro (N=412, 8 weeks, published in CNS Spectrums 2011) reported somnolence in 34% of the extended-release group vs. 14% placebo, and dizziness in 24% vs. 11% placebo [15]. These rates are modestly lower than the 40 to 46% somnolence and 28% dizziness seen with immediate-release in the original label data.

Oleptro was discontinued from the U.S. Market in 2015 for commercial (non-safety) reasons. Generic trazodone immediate-release remains widely available and is the formulation referenced by most prescribing clinicians today.

Clinical Takeaways for Prescribers and Patients

Trazodone's benefit-risk profile differs substantially by dose range. At 25 to 100 mg/day for insomnia, somnolence is the dominant adverse effect but serious events are uncommon. At 150 to 400 mg/day for depression, the full adverse event spectrum applies.

Prescribers should counsel male patients explicitly about priapism before initiating therapy, document the conversation, and instruct patients to seek emergency care for any erection persisting beyond 4 hours. The FDA label states this instruction in mandatory labeling language [1].

Patients over 65 taking trazodone for insomnia should be assessed for fall risk at each visit. A standardized fall-risk screen (such as the STEADI algorithm recommended by the CDC for adults 65 and older) should be applied at baseline and at any dose increase [16].

In adults with a baseline QTc of 450 ms or longer, an alternative agent should be considered before initiating trazodone at doses above 150 mg/day.