Can You Overdose on Cannabis?

Greening out (also called a 'whitey' or cannabis overdose in common slang) occurs when you consume more cannabis than your body can comfortably handle. Symptoms include: extreme dizziness or lightheadedness, nausea or vomiting, rapid heart rate, sweating and chills, anxiety or panic, paranoia, confusion, and feeling faint or shaky.

Greening out is most common with edibles (due to delayed onset leading to overconsumption), high-THC concentrates, and in people with low tolerance. It can also happen to experienced users who accidentally consume more than expected.

The experience is extremely unpleasant but not medically dangerous. Most episodes resolve on their own within 1-4 hours. The effects of edibles can last longer — up to 8-12 hours — but the peak discomfort usually passes within a few hours.

First-time cannabis users should be especially careful. Starting with a very low dose (2.5mg THC for edibles, one small puff for vaping) in a safe, comfortable environment dramatically reduces the risk of greening out.

Step 1: Stay calm. Remind yourself that no one has ever died from cannabis. You are not in danger. The effects will pass. Panic makes everything worse, so take slow, deep breaths.

Step 2: Find a comfortable, quiet space. Lie down if you feel dizzy or nauseous. Reduce stimulation — turn off bright lights, loud music, and screens. Put on something calming like ambient music or a familiar show.

Step 3: Drink water and eat something. Food helps absorb THC and can reduce discomfort. Black pepper contains beta-caryophyllene, which can counteract THC's effects — chewing a few peppercorns or smelling freshly ground pepper can help.

Step 4: CBD can counteract THC. If you have CBD oil or gummies on hand, taking 25-50mg CBD can reduce anxiety and paranoia. This is one reason having a CBD product available is a good idea whenever you try a new THC product.

Step 5: If symptoms are severe or last longer than expected, call NHS 111 for medical advice. Go to A&E only if you have chest pain, trouble breathing, severe vomiting, or are unable to stay conscious.

Cannabinoid Hyperemesis Syndrome (CHS) is a rare condition that affects a small percentage of long-term, heavy cannabis users. It causes cyclical episodes of severe nausea, vomiting, and abdominal pain.

CHS has three phases: prodromal (morning nausea without vomiting), hyperemetic (intense nausea and vomiting, often leading to dehydration), and recovery (symptoms subside after stopping cannabis use).

The only reliable treatment for CHS is complete cessation of cannabis use. Hot showers or baths often provide temporary relief during episodes — this is one of the diagnostic signs of the condition.

CHS is poorly understood and often misdiagnosed. If you experience regular unexplained nausea or vomiting, especially if you're a regular cannabis user, consult your GP and mention the possibility of CHS.

While cannabis alone cannot cause a fatal overdose, combining it with other substances significantly increases health risks. Understanding these interactions is crucial for harm reduction.

Alcohol

The most common combination. Alcohol amplifies THC's psychoactive effects and increases the rate at which THC enters the bloodstream. This can cause severe dizziness, nausea (often worse than greening out alone), impaired coordination, and increased anxiety. The risk of vomiting and dehydration is much higher. Avoid drinking heavily if you plan to use cannabis. For more on safer consumption, see our Social Cannabis Guide.

Opioids & Benzodiazepines

Combining cannabis with opioids (codeine, morphine, fentanyl) or benzodiazepines (diazepam, Xanax) can lead to excessive sedation, slowed breathing, and reduced heart rate. While this combination is rarely fatal, it significantly increases the risk of accidents, falls, and respiratory depression. Use extreme caution or avoid entirely.

Stimulants

Cocaine, amphetamine, and MDMA combined with cannabis can mask the effects of each, leading users to take more of one or both than intended. Cannabis can also increase heart rate — combining it with stimulants adds further cardiovascular strain. Anyone with a heart condition should avoid this combination.

Psychedelics

Cannabis potentiates (strengthens) psychedelic experiences. This can be pleasant at low doses but can also trigger overwhelming anxiety, paranoia, and panic — especially with high-THC cannabis. If combining, use very small amounts of cannabis and stick to CBD-dominant products.

For a detailed overview of known drug interactions with cannabis, see our Cannabis & Medication Interactions Guide. If you take prescription medications, always check with a pharmacist or doctor before using cannabis.