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PGR Weed – What Is Plant Growth Regulators and How to Spot it

Are synthetic plant growth regulators bad for you?
26 April 2022
8 min read
PGR Weed – What Is Plant Growth Regulators and How to Spot it

  • 1. What is pgr weed?
  • 2. What are the most common pgrs?
  • 2. a. Paclobutrazol
  • 2. b. Daminozide (alar)
  • 2. c. Chlormequat chloride
  • 3. Pgr weed side effects
  • 3. a. Short-term effects
  • 3. b. Long-term effects
  • 4. How can you spot pgr cannabis?
  • 5. Pgr vs non-pgr weed
  • 6. Why do growers use pgrs in cannabis cultivation?
  • 7. Evidence for pgrs' being dangerous
  • 7. a. Potential threat to human health
  • 7. b. Environment pollutants
  • 8. What pgr natural alternatives are there?
  • 8. a. Chitosan
  • 8. b. Triacontanol
  • 9. Conclusion
  • 10. Faq
  • 10. a. What is pgr strain?
  • 10. b. What are pgr buds?
  • 10. c. Is pgr weed common in the uk?
  • 10. d. What are pgr chemicals?
  • 10. e. Is pgrs legal?

Those of you who grow your own cannabis may have not even heard of PGRs, but even for you, there is a small chance of encountering these potentially dangerous chemicals in various plant stimulants and boosters. Those who buy their bud – whether in licensed shops or from street dealers – are at an even greater risk of inhaling harmful PGRs with their smoke. So what is PGR weed exactly?

What is PGR Weed?

The term PGR weed refers to bud harvested from cannabis plants that have been cultivated with the use of plant growth regulators, or PGRs for short. These compounds mimic the effects of natural plant hormones and have been known for at least since the 1920s. For decades, farmers were more than happy to use PGRs on different crops for the simple reason that they ensured faster and more generous harvests.

The acute effects of ingesting PGRs were mild enough to go unnoticed, and the long-term harm is usually hard to blame on something specific. So for a long time, PGRs were used for various food crops and haven't been banned in every country to this day. It's only natural that unscrupulous cannabis farmers in a largely unregulated and often illegal industry have embraced PGRs to maximize their profits.

PGR Weed – What Is Plant Growth Regulators and How to Spot it: Two closely trimmed brownish nuggets

The appearance of a PGR-grown bud.

What are the Most Common PGRs?

There are many PGRs that have been used in agriculture and landscaping over the years, but the following three are the most commonly used in cannabis cultivation.


Paclobutrazol is an organic compound that retards growth. Contrary to what you may think, this feature can be very useful to marijuana farmers as it leads to shorter internodes, stouter stems, less stretchy plants, and faster onset of flowering. Plants receiving this PGR are more resistant to drought. Its use may also manifest in darker leaves. Paclobutrazol is mildly irritating to the eyes and skin. Although many PGRs are toxic to different organs, cause cancers, and lead to the birth of deformed babies, Paclobutrazol shows no evidence for any of this.

Daminozide (Alar)

Used to make cannabis buds more firm and attractive, Daminozide, also known as Alar and by several other names, was a popular PGR in the fruit-growing industry, but it was banned in the 1980s. The reason was that when this chemical gets metabolized in your body, it produces dimethylhydrazine which is a highly carcinogenic chemical. If you care about your health, stay away from the weed cultivated with Daminozide.

Chlormequat Chloride

This organic compound also prevents cell elongation. As a result, the flowering stretch that happens at the beginning of the flowering stage in cannabis ends faster and the plant redirects its energy to bud formation. By using Chlormequat, farmers get more compact bushes with stronger branches and denser buds. Moreover, buds require less time to mature. This PGR is deemed extremely hazardous in the US and prohibited for use in plants meant for human consumption.


The Most Common PGRs in Cannabis
Active IngredientFunctions
AncymidolGrowth inhibitor
Gibberellic acidIncreases fruit production
CytokininEnhances color and growth
Chlormequat chlorideInhibits stem growth
PaclobutrazolPromotes uniform flowering and reduces internodal space

PGR Weed Side Effects

Even when PGRs were used everywhere, farmers who sprayed them on their crops always wore protection. It's because most of the plant growth regulators are anything but harmless.

Short-Term Effects

Exposure to PGRs may lead to skin irritation and reddening of the eyes. In extreme cases, you may have trouble breathing and feel nauseous. However, these acute effects are nothing compared to the long-term harm they cause. 

Long-Term Effects

Inhaling some of the PGRs and their ingestion with food may cause damage to your liver, kidneys, and nerve tissue. They are especially toxic for the human reproductive system in both men and women. In men, they may cause infertility, and in women, they are teratogenic, meaning they may cause malformations in babies.

PGR Weed – What Is Plant Growth Regulators and How to Spot it: A bearded young man smoking from a water bong

PGRs can be harmful to humans if consumed in high quantities.

How Can You Spot PGR Cannabis?

We believe you've heard enough to never use PGRs in your own marijuana garden. However, if you buy your smokes, you should be aware that some stuff on the market is cultivated with PGRs. This means you should be able to tell PGR cannabis from a natural herb, and these are the tell-tale signs:

  • unusually dense and heavy buds,
  • too round shape and smooth texture,
  • a spongy feel,
  • too many brown or red pistils (hairs),
  • dull brownish color,
  • too few trichomes (crystals) and low THC (potency),
  • a weak smell or a complete lack of odor,
  • a chemical taste of the smoke,
  • an intense, short-lived high with a headache.

PGR Weed – What Is Plant Growth Regulators and How to Spot it: A side-by-side comparison of natural and PGR buds

Basic differences of regular-grown and PGR-grown buds.

PGR vs Non-PGR Weed

If you have ever held marijuana buds in your hands or maybe even grown them, you'll find no difficulty telling natural cannabis from PGR cannabis. Buds that are airy and loose are obviously above suspicion. But what about super tight and dense nuggets? Are they PGR-enhanced? Or maybe the grower was THAT good? Look at the number of trichomes and check out the smell. If the bud is frosty and has a pungent smell, it's most probably okay. Another reliable sign is the number of brown hairs – a bud should never look like a lollipop that's been rubbed against a rug.

Why do Growers Use PGRs in Cannabis Cultivation?

The short answer is money. Cannabis is sold by weight, and increasing the weight of the harvest is something that PGRs are very good at. The quality suffers, of course, but on the black market (where the majority of PGR weed is sold), people buy what's available, and often they simply don't know enough to tell natural buds from their PGR-modified counterparts. PGRs let unprincipled farmers achieve the following:

  1. During the flowering stretch which happens in the first 2-3 weeks of the flowering stage, they quickly switch the plant from elongating stems to producing bud sites.
  2. During the bulk phase, PGRs make plants rapidly increase their flower mass.
  3. In the weeks leading to the harvest, plant growth regulators contribute to making the flowers super dense and heavy.

All of the above leads to bigger, more compact, and perfectly structured buds. The lack of frostiness is a huge downside, but the most unethical growers and dealers remedy that by sprinkling laundry detergent or even crushed glass on the flowers to imitate crystals. Horrors like this make you wanna grow your own all the more, don't they?

PGR Weed – What Is Plant Growth Regulators and How to Spot it: A handful of greenish tight PGR buds

PGR's can be used to get denser buds, although denser doesn't mean more cannabinoids.

Evidence for PGRs' Being Dangerous

PGRs are a wide class of substances, and only a few of them have been extensively studied for their effects on human health as well as their potential harm to the environment. Especially worrying are those plant growth regulators that interfere with normal plant hormones. We've already talked about three of them – Paclobutrazol, Daminozide (Alar), and Chlormequat Chloride – and their dangers, but the matter is very grave and so worth repeating.

Potential Threat to Human Health

There's no consensus among different countries on whether to ban the use of PGRs in agriculture or allow it. So, some do and others don't. The dangerous side effects of PGRs are definitely there, but they're associated with large doses – much larger than those you're likely to encounter in your food grown with PGRs. However, if you value your health and read the labels on groceries that you buy, you should also stay away from PGR cannabis. These synthetic chemicals are linked to cancer and liver damage, poor reproductive rates, and malformed embryos in mammals.

Environment Pollutants

The strain PGRs put on ecosystems is equally worrying. These chemicals seep into the soil and then get washed into lakes and rivers. There's evidence that at least one of the PGRs – Paclobutrazol – is toxic to fish and their embryos. The use of plant growth hormones also leads to the reduction of biodiversity in the soil, meaning they probably kill some microorganisms.

PGR Weed – What Is Plant Growth Regulators and How to Spot it: PGR marijuana plants growing in a commercial greenhouse

PGRs are mostly used by commercial growers who want to get better yields faster.

What PGR Natural Alternatives are There?

One shouldn't forget that synthetic PGRs mimic the action of natural hormones that plants themselves produce to self-regulate. That's why they're so effective – they simply act on existing, natural pathways. So, if the idea of biohacking your favorite plant is tempting to you, try the following organic PGRs. And don't be fooled by their chemical-sounding names. These two come from nature.


Chitosan is a compound that is abundant in chitin which in its turn is the building material of exoskeletons of insects, lobsters, shrimp, etc. Chitosan is a powerful agent that contributes to faster growth, more efficient photosynthesis, and better nutrient uptake. Even NASA takes an interest in using this natural PGR to grow plants in space! And the best part is that this chemical is non-toxic. 


Triacontanol comes from beeswax but can also be found in sugarcane and alfalfa meal, and no one will suspect any of these three to be hazardous. This natural stimulant speeds up metabolic processes in plants, leading to more efficient photosynthesis, nutrient uptake, CO2 assimilation, and more.

PGR Weed – What Is Plant Growth Regulators and How to Spot it: Many budding cannabis plants in an indoor setup

Have in mind that synthetic PGRs are dangerous but natural plant growth regulators are not.


PGRs won’t harm you if you smoke them once or twice, but it’s always better to be safe than sorry, so use our tips to avoid PGR-grown cannabis. If you have experience with plant growth regulators, please share your knowledge with fellow growers by leaving a comment in the comment section below!


What is PGR strain?

PGR weed means cannabis buds cultivated with plant growth regulators (PGRs) – synthetic or natural chemicals that mimic plant hormones. There are no PGR strains per se, but any strain of weed can be grown using PGRs.  

What are PGR buds?

PGR buds are a special type of marijuana whose development has been tampered with through the use of plant growth hormones, or PGRs. Such buds have a denser structure, a more even surface, a greater number of brown hairs, weaker smell, and poorer 'frostiness' and potency. They may be also bad for your health.

Is PGR weed common in the UK?

If you live in the UK, you're more likely to encounter PGRs in apples, cherries, and other fruit. PGR weed is something that's more widespread in the US where farmers use these chemicals to make marijuana buds denser and heavier. However, with the spread of the cannabis culture across the Atlantic, PGR weed begins to trickle into the UK as well.

What are PGR chemicals?

PGR chemicals are a class of substances whose action is similar to plants' natural hormones that influence different processes within them. The word 'PGR' stands for 'plant growth regulator'. PGRs are used to shorten branches and make them more robust which in cannabis results in denser, rounder, and heavier buds. 

Is PGRs legal?

The legal status of PGRs varies from country to country. Discovered in the 1920s, they were initially used in agriculture everywhere, but after research linked PGRs to different health issues, nations began to ban them for use in human food and animal fodder. The three chemicals that you're most likely to encounter in marijuana – Daminozide (Alar), Chlormequat Chloride, and Paclobutrazol – are all prohibited in the US, but the latter is still allowed in the UK.


  1. Plant growth regulation. - Haas, Ulrich & Harp, Tyler. (2015).
  2. Plant Growth Regulators. - Basuchaudhuri, Pranab. (2020).
  3. Toxicological characteristics of plant growth regulators and their impact on male reproductive health. - Chun-Shuang Xu, Zhou Jiang, Wei Shen, Shu-Hua Zou. (2018)
26 April 2022