Greening Out: Symptoms, Causes, and What to Do

"Greening out" is the informal name for an unpleasant reaction to too much THC. A person may become pale, sweaty, dizzy, nauseated, frightened, or confused. Their heart may race. Some people vomit or feel as if they are going to faint.

Most otherwise healthy adults recover with time and supportive care. That does not mean every reaction is safe to manage at home. A child who ingests cannabis, a person who cannot be awakened, or anyone with trouble breathing, a seizure, chest pain, severe confusion, or nonstop vomiting needs prompt medical help.

What greening out actually is

THC, or delta-9-tetrahydrocannabinol, is the main intoxicating compound in cannabis. It can affect coordination, perception, memory, heart rate, blood pressure, nausea, and anxiety. When the dose is higher than a person can comfortably tolerate, those effects can become overwhelming.

That threshold is different for everyone and moves around. Tolerance, body size, what and when you last ate, hydration, sleep, anxiety levels, and especially co-use of alcohol all shift it. This is why someone can use the same amount as always and green out "for no reason" — the dose didn't change, but the body's threshold did.

Symptoms

A green-out typically involves several of the following, arriving over minutes (smoking or vaping) or over an hour or more (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

The cannabis available today is not the cannabis of past decades. THC concentrations in illicit and dispensary flower have risen severalfold since the 1990s, and concentrates commonly exceed 60–80% THC. Higher potency means the gap between a comfortable dose and an overwhelming one is narrower — and easier to cross by accident. Edibles add a second mechanism entirely, covered in our companion guide on why edibles hit harder and later. National poison center data reflect the trend, with cannabis exposure calls — particularly edible-related and pediatric cases — rising sharply over the last decade.

What to do when someone greens out

The goal is simple: keep the person safe and comfortable while the THC is metabolized. There is no reversal agent for THC — time is the treatment.

1. Get them somewhere calm, seated or lying down. Fainting from standing up too fast is one of the few ways a green-out causes real injury. If they're lying down and nauseated, position them on their side.
2. Reassure them, specifically and repeatedly. Anxiety can amplify the physical symptoms. Try: "You had cannabis, you are having a difficult reaction, and I am staying with you while we watch your symptoms." Do not promise that nothing is wrong if you are uncertain.
3. Offer small sips of water. Vomiting plus sweating dehydrates. Skip food unless they want it; something bland and a bit of sugar can help 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. CBD does not reliably reverse THC effects despite the folklore.
6. Stay with them. Most green-outs resolve substantially within one to four 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. Call 911 if the child has trouble breathing, collapses, has a seizure, or cannot be awakened.
• 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

Effects from smoked or vaped cannabis usually begin within minutes and often ease sooner than effects from an edible. Edibles can take much longer to start, may continue building for hours, and can impair someone for much of the day. Product strength, dose, tolerance, other substances, and individual metabolism all change the timeline. If symptoms are severe, worsening, or lasting longer than expected, call Poison Control rather than relying on 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 can be a sign of cannabis use disorder. The CDC estimates that about 3 in 10 people who use cannabis have cannabis use disorder, with greater risk among people who begin young or use frequently. Recurrent vomiting in a long-term, frequent user may also point to cannabinoid hyperemesis syndrome, which requires a different response.

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