Poisoning Due to Antidepressants

What to do right now

1. Call 911 or your local emergency number if the person is drowsy, confused, having a seizure, has a fast or irregular heartbeat, or took a tricyclic, MAOI, venlafaxine or bupropion. Otherwise call Poison Help at 1-800-222-1222 in the US for expert advice.
2. Find the medicine packets and note the drug name, strength, how many may be missing and when they were taken. Include alcohol and any other drugs.
3. If the person is unconscious but breathing, place them on their side in the recovery position. If they stop breathing, start CPR.
4. Do not make them vomit and do not give food or drink.
5. Stay with them. If the overdose was intentional, remove other medicines and means of harm, and stay calm and non-judgmental.

How antidepressant poisoning affects the body

Antidepressants act on brain chemicals, but many also affect the heart and nerves, especially in overdose.

Tricyclic antidepressants

Tricyclics cause most serious antidepressant poisonings. They block sodium channels in the heart, which slows electrical conduction and can lead to dangerous ventricular arrhythmias. They also block acetylcholine and alpha receptors. The result is a combination of:

• fast heart rate, low blood pressure and abnormal ECG (wide QRS complex)
• drowsiness, confusion, agitation and coma
• seizures
• anticholinergic signs: hot, dry, flushed skin, large pupils, dry mouth, inability to urinate, absent bowel sounds

Deterioration can be very rapid, sometimes within an hour. See tricyclic antidepressant overdose for more detail.

SSRIs and SNRIs

SSRIs (fluoxetine, sertraline, citalopram, escitalopram, paroxetine) are much safer in overdose. Most people have nausea, vomiting, tremor, drowsiness and a fast heart rate. Citalopram and escitalopram can prolong the QT interval on the ECG and cause seizures in large doses. Venlafaxine, an SNRI, is more toxic and causes seizures, arrhythmias and low blood pressure.

Bupropion

Bupropion overdose commonly causes seizures, sometimes delayed by many hours with extended-release tablets, plus agitation, fast heart rate and, in large doses, heart rhythm problems.

MAO inhibitors

MAOIs (phenelzine, tranylcypromine) can cause delayed, severe toxicity up to 24 hours after overdose, with very high or low blood pressure, high fever and rigidity. They also cause dangerous interactions with other medicines and foods rich in tyramine.

Mirtazapine and trazodone

These mainly cause drowsiness and low blood pressure. Trazodone can cause priapism (a painful, prolonged erection).

Serotonin syndrome

Serotonin syndrome is serotonin toxicity. It can occur after an overdose or when two serotonin-raising drugs are combined, for example an SSRI with tramadol, linezolid, St John's wort, MDMA or an MAOI. It typically develops within 24 hours.

Who is at risk

• people with depression who have thoughts of suicide, particularly in the weeks after starting or changing a medicine
• people taking several medicines that affect serotonin or heart rhythm
• older adults and people with heart or liver disease
• young children who find tablets at home. One or two tricyclic tablets can be dangerous to a toddler

Diagnosis in hospital

• History and examination: which drug, how much and when; pupils, temperature, reflexes and muscle tone.
• ECG: repeated to look for a widened QRS or prolonged QT, the key danger markers.
• Blood tests: electrolytes, kidney function, blood gases, glucose, creatine kinase if rigid.
• Acetaminophen (paracetamol) and alcohol levels: because co-ingestions are common and acetaminophen poisoning is silent at first.

Antidepressant blood levels are not usually needed for treatment decisions.

Treatment

• Airway, breathing and circulation: oxygen, IV fluids and, for coma, a breathing tube.
• Activated charcoal: can reduce absorption if given within about an hour of a significant overdose in someone who is awake and can protect their airway.
• Sodium bicarbonate: given IV for tricyclic toxicity with a wide QRS, arrhythmias or low blood pressure. It protects the heart's sodium channels.
• Benzodiazepines: for seizures, agitation and serotonin syndrome.
• Cyproheptadine: an antidote sometimes used for moderate serotonin syndrome.
• Cooling and intensive care: for severe serotonin syndrome with high fever.
• Observation: at least 6 hours with ECG monitoring after most overdoses, and longer for extended-release products, bupropion and MAOIs.
• Mental health assessment: after any intentional overdose, before discharge.

Outlook

Most people with SSRI overdose recover fully within 24 hours. Tricyclic and MAOI overdoses carry a higher risk of death and lasting harm, but outcomes are good with early hospital care. Recovery from the overdose is also the start of reviewing treatment for the underlying condition.

Prevention

• Store medicines locked away and out of reach of children.
• Ask your prescriber about smaller supplies or a safer medicine choice if you have had suicidal thoughts.
• Tell every doctor and pharmacist about all medicines and supplements you take, including St John's wort.
• Do not combine antidepressants with recreational drugs or alcohol.
• Dispose of unused tablets through a pharmacy take-back program.
• If you notice worsening mood or thoughts of self-harm, contact your doctor or call or text 988.

Frequently asked questions

What are the symptoms of antidepressant overdose?

Symptoms depend on the drug. Common signs are drowsiness, confusion, agitation, tremor, vomiting, a fast heartbeat and dilated pupils. Tricyclics can also cause low blood pressure, seizures and dangerous heart rhythms. Serotonin syndrome adds sweating, muscle jerking and high temperature.

Which antidepressants are most dangerous in overdose?

Tricyclic antidepressants such as amitriptyline and imipramine are the most dangerous because they disrupt heart rhythm and cause seizures. MAO inhibitors, venlafaxine and bupropion are also high risk. SSRIs such as sertraline and fluoxetine are much safer, though citalopram can affect heart rhythm.

How long after an antidepressant overdose do symptoms start?

Most toxic effects begin within 1 to 6 hours. Extended-release medicines such as bupropion XL and venlafaxine XR, and MAO inhibitors, can cause delayed symptoms up to 24 hours later. This is why hospitals monitor patients for several hours even if they seem well.

What is serotonin syndrome?

Serotonin syndrome is a toxic reaction to too much serotonin activity, usually from an overdose or a combination of medicines. It causes tremor, sweating, agitation, diarrhea, muscle twitching and fever. Severe cases cause very high temperature and rigidity, which is a medical emergency.

What should I do if my child swallowed an antidepressant?

Call 911 or Poison Help at 1-800-222-1222 (US) immediately, even if your child seems fine. Even one or two tricyclic tablets can be dangerous to a toddler. Bring the medicine container to the hospital and do not try to make your child vomit.