Why You Sometimes Feel Sick or Vomit After Smoking Weed

The science behind a bad high – AKA pulling a whitey or greening out – explained.
Man vomiting from smoking too much weed in toilet
Photo: Wavebreak Media ltd / Alamy Stock Photo

Ah yes, the abstinence-first drugs education of the late 20th and early 21st century. “Just say no,” Nancy Reagan says on telly as your teacher pushes in another VHS tape showing a scrawny man having a panic attack after a single toke, leaving you to get the rest of your information on weed and bad highs from random 4/20 articles, Snoop Dogg and a Harold & Kumar movie you once watched at a sleepover.


If your childhood was anything like mine, you were told that a single puff might cause you to spontaneously develop a psychiatric disorder. While we can all agree that this is War on Drugs nonsense, it’s also true that you should always indulge in moderation, lest you fall victim to the whitey (or “greening out” for our American friends). Its effects usually start with the room spinning and end with something reminiscent of the opening lines on Eminem’s “Lose Yourself”: knees weak, palms sweaty, and finally, mom’s spaghetti.

Feeling sick and needing to vomit is one of the worst experiences to encounter while smoking weed, so VICE spoke to some experts to find out why you sometimes chunder and how to avoid it. But first, you have to understand a little about the science of cannabis.

How cannabis gets you high  

Enter Dr Mikael Sodergren, the Head of the Imperial College Medical Cannabis Research Group and managing director of Sapphire Medical Clinics, the first medical cannabis clinic approved by regulators in the UK. 

“The euphoria that people feel from cannabis inhalation or any [other] mode of administration is [from] THC [the main psychoactive compound in marijuana] going via the bloodstream through the membrane of your blood that separates your brain from the rest of the body, and into cells in the brain, where it binds to certain cannabinoid receptors,” he explains.


“When the THC binds to these receptors in the brain, they cause a cascade – we call it a signaling pathway – that releases chemicals within certain areas of the brain that cause euphoria.” 

These receptors are part of what’s known as your endocannabinoid system, a complex cell signalling network that runs through the human body and helps to regulate essential functions like appetite, pain control and, yep, nausea and vomiting. 

What is ‘pulling a whitey’ or ‘greening out’?

Pulling a whitey or greening out is essentially down to an “overstimulation of the endocannabinoid system”, Sodergren says. “What happens is: the chemicals that are released in the brain that can cause sickness to be alleviated, cause the opposite effect.” 

So is a whitey caused by overdosing on THC? “You can overdose from anything if ingested in large enough quantities, including water,” Sodergren points out. “Overdoses that directly lead to death from cannabis are virtually non-existent.” 

In some cases, the dizziness caused by a very strong head high as a result of ingesting a large amount of THC can cause you to feel rough. Essentially, just like chocolate or alcohol, too much of a good thing can make you momentarily sick – but that doesn’t mean you’ve OD’ed. In fact, a 2019 coroner’s verdict that ruled THC overdose as the cause of death of a woman in New Orleans was met with scepticism from drug experts.


Some outlets, including under-25s charity The Mix, have claimed that smoking weed causes low blood pressure and makes you feel faint, but Sodergren explains that “the relationship [between cannabis and blood pressure] is not well defined. Some cannabinoids can contribute to further increases in blood pressure”. 

“Cannabis is actually very good for nausea,” notes Dr Peter Grinspoon, a medical cannabis specialist at Massachusetts General Hospital and an instructor at Harvard Medical School, pointing to its benefits for chemotherapy patients who frequently experience side effects of sickness. “It interacts with the [brain’s] capsaicin receptor – capsaicin [is] that stuff on hot peppers – and helps suppress nausea and vomiting. It also works on the central vomiting center in your brain to lower nausea and vomiting.”

“However, occasionally people can have a paradoxical reaction to a medication,” Grinspoon adds, referring to the scientific term for when you experience the opposite effect of what a chemical substance (e.g. a drug) typically does. “It's thought that if you chronically overstimulate that capsaicin receptor, it can start having the opposite reaction and cause more nausea and vomiting, rather than less.”


There’s even a rare condition has been linked to regular and long-term use of marijuana: cannabis hyperemesis syndrome, a rare condition characterised by abdominal pain, recurrent nausea and repeated bouts of vomiting. “People can go from having [weed] help their nausea and vomiting to actually greening out [and] being really sick,” Grinspoon says. “I've seen people throw up for hours – it's really awful.”

If whiteying is an infrequent occurrence, you probably aren’t among the unlucky few with the syndrome. But there are things you can do to make your smoking experience more pleasant. 

How to avoid vomiting from weed

First off: Don’t mixing your weed with tobacco or drink alcohol with your spliff. “Mixing drugs at high doses is probably going to give you a higher likelihood of having an adverse effect, than just having one drug at a high concentration,” Sodergren says. 

He adds that the method of ingestion also doesn’t matter that much: “[When] you reach a similar concentration in the blood, it's gonna make you feel sick, whether you eat it, smoke it or vape it” – though he notes that smoking hits the bloodstream quicker than edibles, which can cause you to feel sicker more quickly.

Grinspoon finishes with some sage advice on the best way to avoid greening out: “Keep the doses low and know yourself. If it happens to you, try to do a postmortem on what happened, like: ‘Was there alcohol involved? Was there nicotine involved?’ Was I overtired? Did I take five puffs when I usually take two puffs?’”

So if you’re going to smoke – particularly if you haven’t done so in a while – take it slow and go easy on yourself.