PGR weed – what exactly is it?

PGR weed: person looks at cola under microscope

As consumers become knowledgeable about what they’re smoking and regulators establish safeguards on cannabis operations, PGR weed isn’t the most popular option. But there was a time when lots of medical-grade cannabis flower was grown with PGRs.

The acronym PGR stands for plant growth regulator. These are natural or synthetic plant hormones that bulk up buds for a heavier pack, AKA more money for cultivators. The catch is that synthetic PGRs have had a long-term negative impact on many people who apply them and those who consume them.

PGR weed: tons of cannabis in veg
Photo by MATIJA KEBER for Getty Images

Joshua Mezher, founder and CEO of a Pot for a Pot, was growing cannabis when synthetic plant growth regulators were first recommended. He answered questions about his experience growing cannabis with plant hormones via email.

“In the medical cannabis days of Cali, before it was recreational, no one really had a concept of ‘PGR’ or that it was bad for the end product or humans,” Mezher shared. “Products with paclobutrazol and chlormequat chloride were kept behind the counter and out of sight of any CDFA inspectors. The guy at the hydro shop was advising growers to use it because it makes buds super dense or helps keep plants short.”

RELATED: Hemp clothing for a fashionable, sustainable future

Cannabis cultivators have always wanted to grow fire with red hairs, frosty trichomes, and bulky buds. So when offered an easy doorway to heavier packs, most were beyond interested. But this practice has become banned by regulated states in response to the impact of plant growth hormones on human health.

Types of PGRs

Moriah LaChappell, a Senior Account Advisor for Wilbur-Ellis Agribusiness, serves as a technical resource for nursery, greenhouse, and organic farmers. Vineyard, coffee, and cannabis farmers commonly ask her about PGRs.

“Before the states legalized cannabis, PGRs were often used to create more compact growth and encourage uniform branching,” explained LaChappell, “This enhanced plant structure improved floral initiation and potential yield.”

The synthetic PGR most commonly used on cannabis plants is paclobutrazol, a fungicide that reduces the space between roots and shoots in plants. That means the flowers are more compact and dense, ideal for commercial operations. It is also common practice for food crops like mango, peach, and persimmon to delay fruit maturation and lead to more weight in the grocery checkout.

Chlormequat chloride also has a history in the cannabis garden. The PGR was discovered in 1950 and shortens stem length between flowers. It is most effective when applied directly to the plant, and is commonly used on wheat and grains.

These hormones were designed for commercial flower operations and wheat, not for cannabis buds. This leads many to wonder how PGR cannabis tastes and whether it’s safe for human consumption.

Is PGR weed bad?

Cannabis grown with plant growth regulators turns out more dense. Mezher shared that this is where the term “golf ball nugs” comes from. But golf ball nugs are no longer a coveted feature. Despite the initial “wow” factor, PGR buds have fewer whole, juicy trichomes. This results in less terpenes and cannabinoids, meaning subpar taste and effect.

“When using PGRs specifically designed to increase trichome production, the bud would have lots more trichomes, but the heads would be underdeveloped, leaving you with a sugar-coated bud that was less potent than it might appear,” Mezher explained.

Many consumers have reported that flowers grown with PGRs don’t hit like nugs from organic or veganic cannabis plants. But there are also health implications from seed to sale. Growers applying paclobutrazol must be careful, as one 2022 study showed that contact with the PGR can disrupt thyroid function.

People can experience skin and eye irritation or liver damage if overexposed to chlormequat chloride. With that in mind, one might question whether heating and inhaling a cannabis product grown with synthetic hormones is wise.

RELATED: Cute bongs perfect for Barbie summer

PGR weed: cannabis cola
Photo by Marco VDM for Getty Images

Natural PGR weed

Synthetic PGRs are not allowed in regulated cannabis cultivation, but there are natural alternatives. Mezher explained that the willow tree has a hormone called indolebutyric acid that inhibits rooting, and that’s not all nature has to offer.

“The approved natural plant growth regulator is kelp,” added LaChappell. “Kelp contains cytokinins. Cytokinins (CK) are a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. When applied as a foliar before floral development they can create more compact internodes. This is the correct product because it’s an EPA-registered organic cytokinin.”

For those still wondering if it’s safe to smoke PGR weed, the answer is: maybe sometimes. There are natural plant growth regulators. In other words, PGR isn’t always synthetic. But it may be wise to pass on plants grown with paclobutrazol or chlormequat chloride.

If health implications aren’t enough to sway public opinion, let Mezher’s experience describe why PGR weed may not be the bee’s knees.

RELATED: Protecting pets from pot poisoning

“Often they would have lots of bag appeal but would turn to boof once ground up and put into a joint. Nowadays, if you get a rock-hard nug, there is a good chance it has seen a PGR.”

It doesn’t matter whether a consumer values their health or their high—synthetic PGR weed lacks luster on both accounts. Know the signs and avoid that bodybuilder bud for a more desirable experience.

Cara Wietstock is Senior Content Producer of and has been working in the cannabis space since 2011. She has covered the cannabis business beat for Ganjapreneur and The Spokesman Review. You can find her living in Bellingham, Washington with her husband, son, and a small zoo of pets.