Greening Out: Symptoms, Causes, and What to Do

"Greening out" is the informal name for an unpleasant reaction to too much THC. The person goes pale and sweaty. They may get dizzy, nauseated, frightened, confused. The heart races. Some people vomit; some feel certain they are about to faint.

Most otherwise healthy adults get through it with time and supportive care, and that sentence should not be read as "every reaction is safe to manage at home." A child who ingests cannabis needs prompt medical help. So does a person who cannot be woken, and so does anyone with trouble breathing, a seizure, chest pain, severe confusion, or vomiting that will not stop.

What greening out actually is

THC — delta-9-tetrahydrocannabinol — is the main intoxicating compound in cannabis. It affects coordination, perception, memory, heart rate, blood pressure, nausea, and anxiety. Push the dose past what a particular body can tolerate that day and those effects stop being recreational and start being overwhelming.

The frustrating part is that the threshold moves. Tolerance, body size, what and when you last ate, hydration, sleep, baseline anxiety, and especially alcohol on board all shift it around. This is how someone uses their usual amount and greens out "for no reason." The dose didn't change. The body's threshold did.

Symptoms

A green-out typically involves several of the following, arriving over minutes when smoked or vaped, or over an hour or more with edibles:

• Nausea and vomiting — often the defining feature
• Dizziness or the sensation the room is spinning, especially when standing
• Pale, clammy skin and cold sweats
• Rapid heartbeat and awareness of the heart pounding
• Drop in blood pressure — lightheadedness, tunnel vision, occasionally fainting
• Anxiety, dread, or panic, sometimes with a feeling of unreality
• Confusion or slowed thinking
• Shakiness or chills

Why it's happening more

Today's cannabis is not the cannabis of past decades. THC potency in cannabis seized by law enforcement rose from 3.96% in 1995 to 16.14% in 2022, according to NIDA, and dispensary flower and concentrates can exceed 40%. Higher potency narrows the gap between a comfortable dose and an overwhelming one, and a narrow gap gets crossed by accident. Edibles add a second mechanism entirely — covered in our companion guide on why edibles hit harder and later. National poison center data tell the same story: cannabis exposure calls, particularly edible-related and pediatric cases, have risen sharply over the last decade.

What to do when someone greens out

The goal is simple. Keep the person safe and comfortable while their body metabolizes the THC. There is no reversal agent — time is the treatment.

1. Get them somewhere calm, seated or lying down. Fainting after standing up too fast is a common way people get hurt during a green-out. If they're lying down and nauseated, put them on their side.
2. Reassure them, specifically and repeatedly. Anxiety amplifies every physical symptom on the list. Try: "You had cannabis, you are having a difficult reaction, and I am staying with you while we watch your symptoms." Do not promise nothing is wrong if you are not sure of that.
3. Offer small sips of water. Vomiting plus sweating dehydrates. Skip food unless they want it; something bland with a bit of sugar is fine if they do.
4. Cool them down. Fresh air, a fan, a cool damp cloth on the neck or forehead.
5. Do not add anything. No alcohol "to take the edge off," no other substances, no more cannabis. And no, CBD does not reliably reverse THC effects, whatever the folklore says.
6. Stay with them. Smoked or vaped reactions often ease within a few hours. Edible reactions run longer. Someone should remain present until the person is clearly recovering.

When to get medical help

Call 911 or go to an emergency department if any of the following occur:

• The person is unresponsive or can't be woken
• Seizure activity
• Trouble breathing or bluish lips
• Chest pain, or a racing or irregular heartbeat that isn't settling
• Repeated vomiting that won't stop, or signs of significant dehydration
• A child may have ingested cannabis. Contact Poison Control immediately. If the child collapses, has a seizure, has trouble breathing, or can't be awakened, call 911.
• The product may have been counterfeit or contaminated, or the person took other substances alongside it
• Severe agitation, paranoia, or any talk of self-harm — for a mental health crisis, call or text 988

How long it lasts

Smoked or vaped cannabis usually announces itself within minutes and eases sooner. Edibles are the opposite problem: slow to start, capable of building for hours, and able to impair someone for much of a day. Product strength, dose, tolerance, other substances, and individual metabolism all bend the timeline. If symptoms are severe, worsening, or outlasting what seems reasonable, call Poison Control instead of trusting the clock.

If this keeps happening

An occasional miscalculation is one thing. A pattern is information. Continuing to use cannabis despite repeated physical or psychological problems is one of the signs of cannabis use disorder. In 2025, an estimated 19.3 million people aged 12 or older had a past-year cannabis use disorder, roughly 3 in 10 of the 61.6 million who used cannabis in the past year, according to SAMHSA's National Survey on Drug Use and Health. Risk is higher for people who use frequently or start young. And recurrent vomiting in a long-term, frequent user may point to cannabinoid hyperemesis syndrome, which is a different problem requiring a different response.

If use has become hard to moderate, one honest conversation with an addiction-trained clinician is worth more than another round of trial and error. Our treatment options guide explains what level of support typically fits different situations, and SAMHSA's helpline (1-800-662-4357) offers free, confidential referrals 24/7.