THC-Blood Levels Can’t Be Determined Postmortem, Research Finds

The role of cannabis in vehicular crashes remains one of the most controversial aspects of legalization. A new study produced by a Colorado researcher threatens to upset one of the supposed scientific certainties about impairment and blood-THC levels.

A new study threatens to upset one of the supposed scientific certainties about impairment and blood-THC levels.

Andrea Tully, a graduate student researcher at the University of Colorado, looked at the blood draw methods and THC level results from 100 recently deceased subjects at the El Paso County Coroner’s Office in Colorado Springs.

Each subject tested positive for THC, but when comparing blood drawn from different parts of the body, Tully found dramatic disparities in THC levels. She also found disparities in THC levels drawn soon after death, compared to blood drawn hours or days later from the same subject.

Her conclusions throw doubt on the growing pool of data in legal states on fatal vehicle crashes supposed caused by THC impairment. “Reaching a verdict on the level of impairment of a deceased individual,” Tully wrote, “can prove to be risky and possibly reckless,” due to the many uncontrolled variables she uncovered in postmortem blood draws.

This has the potential to be a politically explosive statement.

THC-Impairment Data as a Political Weapon

Anti-legalization groups like SAM and the Rocky Mountain High Intensity Drug Trafficking Area group have gone to great lengths to publicize a purported rise in the number of fatal traffic crashes due to THC impairment. That data is often based on postmortem blood draws taken from drivers involved in a fatal crash.

Most legal states have adopted 5 ng/mL (nanograms per milliliter) of THC in the blood as the per se limit. Anything under that is considered legal; over that is grounds for arrest on a DUI charge, regardless of the actual impairment of the driver. When a driver killed in an auto crash is suspected of being impaired, their blood is drawn postmortem, sometimes hours or days after death.

As the Body Decays, THC Migrates

In her research, Tully found that delay skewed the data. The longer the time interval between death and the blood draw, the higher the THC level in the blood. She attributed that to the phenomenon of postmortem redistribution.

“Postmortem redistribution describes the movement of drugs within the body after death,” Tully noted, “with the result that the blood concentration of a drug is significantly higher at autopsy than immediately after death.”

That redistribution happens in part because organs that contain high concentrations of THC (such as the lungs and liver) release THC into nearby blood vessels at death.

THC levels also vary widely in different parts of the body. Tully found that blood draws from one subject varied from 2.1 ng/mL (under the legal limit) to 6.6 ng/mL (above the legal limit) depending on where blood was drawn in the body, while another subject’s THC levels varied from 2.9 ng/mL to 40.9 ng/mL.

Quality of Blood Sample Affects THC Level

Regarding the condition of the blood samples taken, Tully also found that “as the quality of the sample decreases, the concentration of THC increases.”

For example: One draw that contained a high amount of fat registered a high level of THC, most likely due to the fact that THC is highly lipophilic, so it tends to concentrate in fat cells. That fat-heavy sample registered nearly three times the THC level as a cleaner blood sample taken from the same subject.

Her research offers no conclusions about THC and impairment in living drivers, only about the accuracy of blood-THC levels gathered from postmortem blood draws. “Colorado has a statewide DUID limit of 5 ng/mL of parent THC in blood,” which is calculated based on blood samples taken from living drivers, Tully wrote. “However, making such a judgment call in deceased individuals is not so simple.”

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How to Grow Cannabis for Concentrate Production

Cannabis is most commonly consumed in its flower form, so many growers focus on getting high yields to increase profits. But some are choosing to focus on the burgeoning concentrate market instead.

Growing for concentrates is slightly different than growing for flower because the end goal is to have a plant that produces a lot of trichomes, in order to have that flower then processed. Trichomes are the glandular crystals that form on cannabis buds that contain cannabinoids and terpenes. They can also be referred to as resin, crystals, or sugar.

The cost of sending your material off to be processed for concentrates can be a financial deterrent for some growers, however, with rosin pressing technology, many growers are now able to process their own concentrates to get high-end oil.

Here we’ll flip the script and look at how to focus your garden for growing plants that will produce great concentrates.

What Makes a Good Plant for Concentrates

If you are going to concentrate the flavors of a strain, it’s best to start with something that already has a delicious flavor and high that you like.

To get a good concentrate, you’ll need to start with good flower. The best concentrates are extracted from quality flower that produces bulbous trichome heads.

Plants that produce large trichome heads will have more oils, which in turn can hold more cannabinoids and terpenes, making them able to produce more flavorful concentrates.

It’s especially important to have big trichome heads when making solventless hash because they’ll break off easier in the hashmaking process.

Strains with complex terpene profiles with multiple terpenes can produce unique flavors. Sometimes trading a high yield for novelty is worthwhile–complexity and rarity can make for a great concentrate. If you have a special strain, making it into a concentrate can let you further appreciate its subtle qualities.

How to Improve the Quality of Your Plants

Because concentrates focus in on a strain’s terpene and flavor profile, you don’t want unwanted compounds like those found in pesticides and nutrients to end up in your concentrates. Here are some ways to improve the quality of your plants while protecting and preserving terpenes.

Use a Complete Soil

This soil comes loaded with most of the nutrients your plants need, all in organic form, making it easier for roots to uptake them.

Avoid Foliar Spraying

Foliar spraying helps combat nutrient deficiencies and pest problems, but you want to avoid this practice when plants are flowering, as the residue will show up as a contaminant in your concentrate. If you do need to spray plants, do so before flowering begins and only use organic sprays.

No Pesticides

Stay away from hazardous chemicals that can’t be flushed out of your crop. These will carry through into your concentrates and are dangerous to consume. Consider using integrated pest management strategies, predatory mites, or organic foliar sprays to keep your garden healthy without impacting your flower.

Flush Your Crop

If growing with non-organic fertilizers or nutrients in a soil or hydro-based medium, give your plants only water in the last two weeks of flowering before harvest. This will give them time to flush out impurities, making for cleaner flower and therefore a cleaner concentrate.

Tips and Tricks for Increasing Trichome Production

These simple methods can make a big impact and greatly improve the quality of your end product.

Room Temperature

Specific terpenes start to break down around room temperature, making climate control in your grow room essential for the quality of your concentrate’s flavor. You can use a climate-control system–and even an infrared heat reader–to observe the temperature of your colas when plants are flowering. Ideally, you want your canopy to be below 75 degrees.


CO2 is an essential part of photosynthesis and without it your plants will not be able to fully utilize nutrients. Give your plants a boost with a CO2 burner to increase the size of your plants during both the vegetative and flowering phases. Bigger plants will have more surface area and therefore more resin because of the higher yields.

Finishing Cold

This is open to debate, but some growers argue that reducing the temperature in your grow room right before harvest can cause cannabis plants to increase their trichome production.

The idea is that the stress created by lowering the temperature will make a cannabis plant produce more trichomes in an attempt to protect itself. When a plant is about to die, it will produce more resin to attract more bugs in order to pollinate. Some growers will even cut off a plant’s watering a few days before it’s harvested to induce stress

Consider lowering the temperature to the low 60s no more than 2 weeks before harvest, when buds are mostly done growing.

What to Do After Harvest

The last step in accentuating delicious terpenes in your cannabis comes at harvest. Some growers freeze their buds without curing before making concentrates, while others prefer to cure prior to making concentrates.

Here are some different approaches to how to preserve terpenes post-harvest.


Freezing prevents terpenes and cannabinoids from breaking down and captures the fresh profile of a plant when its terpene content is the highest.

If you are planning to make a concentrate within a couple weeks after harvest, you can skip the curing process altogether and freeze your buds. You’ll want to remove fan leaves and buck down the colas until all buds are no larger than a golf ball or so and then package the buds.

Drying and Curing

If you’re not sure if you’re going to turn your flower into concentrates at harvest time, properly drying and curing your plants is a must for protecting trichomes. Hang your plants so they have plenty of space to breath in a room with good air circulation, at a temperature between 60-70?F with a humidity of 45-55%.

When drying is complete, put your buds into glass jars where they can cure slowly, popping off the lids (a.k.a. burping) a few times a day at first to let the buds breath and release moisture. Overtime, opening the jars will become less necessary and the buds will continually improve, usually for up to 6 months.

As mentioned previously, some terpenes will break down at room temperature (70?F), so keep curing temps between the high 50s and mid-60s with 55% humidity to maintain quality.

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Louisiana House Unanimously Approves Bill to Allow CBD Sales

BATON ROUGE, La. (AP) — Lawmakers have broadened a proposal to legalize the growing of industrial hemp in Louisiana to also create a regulatory framework for CBD product sales.

State officials have suggested CBD products and sales are illegal in Louisiana.

CBD is a non-intoxicating molecule found in cannabis that some believe is beneficial to their health. State officials have suggested CBD products and sales are illegal in Louisiana.

Language added to the bill by Republican Rep. Clay Schexnayder would prohibit sales of alcohol or food containing CBD, unless the FDA approves the substance for such use. It outlines a process for selling other CBD products.

The growing and processing of hemp, a relative of the marijuana plant used in textiles and fuels, would comply with the 2018 federal Farm Bill.

The House voted 102-0 for the measure, sending it to the Senate.

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Cannabis and the Immune System: A Complex Balancing Act

Cannabis sativa has been consumed for health and nutritional purposes for thousands of years. Many ancient civilizations – from the Chinese to the Greeks – included cannabis in their pharmacopoeia. Back then, no one questioned how or why cannabis relieved pain and calmed the spirits. It was a helpful ally – that’s all that mattered.

Fast forward to the 21st century. Scientists are trying to understand not only the molecular makeup of cannabis, but also how it interacts with the complex web of biological systems in our bodies. Yet, despite many exciting discoveries, we still know relatively little, especially when it comes to the interplay between cannabis and the immune system.

Some studies suggest that cannabinoids like THC and CBD are immunosuppressant, which can explain the relief experienced by medical cannabis users with autoimmune diseases and chronic inflammation. Other studies have shown that regular cannabis use can increase white blood cell counts in immunodeficiency disorders such as HIV, suggesting an immune-boosting effect.

It gets even more complicated when we consider that the effects of cannabis are mediated primarily by the endocannabinoid system, which scientists believe interacts with all biological activity, including our immune system.

The bottom line is that much remains to be discovered about how cannabis affects our immune system. Here’s some of what we know so far.

Our Immune System – an Overview

We are constantly exposed to infectious diseases, bacteria and viruses (antigens), all intent on running amok and wreaking havoc. Without any inbuilt defences to keep these invaders at bay, we’d all last about five minutes on this planet. Thank goodness we have an immune system: the complex network of cells, tissues and organs, running with military precision to keep us healthy.

A key player in the immune system’s arsenal are white blood cells or leukocytes, which seek out and destroy any unwanted visitors. Leukocytes can be divided into two groups: 1) lymphocytes (B cells and T cells) that destroy antigens and help the body to remember previous attackers; and 2) phagocytes that absorb and neutralize foreign intruders.

Many of us are familiar with T cells because of their relationship with the HIV virus, which wipes them out; this is what makes HIV patients vulnerable to normally harmless infections.

Our immune system also plays a key role in detecting malfunctioning cells inside our bodies, and, through the process of apoptosis or cell death, ensures that these cells do not continue to grow and become tumors.

Killing cells is a crucial element of a healthy functioning immune system, which maintains a delicate balance between growth and death. If, for example, there is too much cell death, autoimmune diseases can result, while too little can create the perfect environment for cancer.

The Endocannabinoid System and the Immune System

Optimum immune function entails a complex balancing act that relies on constant communication between our immune cells, tissues, and organs. With the discovery of the endocannabinoid system (ECS) in the 1990s, scientists have found another key piece of the puzzle.

The endocannabinoid system comprises two main G protein-coupled receptors (CB1 and CB2), endogenous ligands known as endocannabinoids (anandamide and 2-AG), plus the proteins that transport our endocannabinoids and the enzymes that break them down in the body.

Endocannabinoids are produced on demand, travelling backwards across chemical synapses and modulating cell activity. This partly explains why the ECS has been termed a homeostatic regulator – continually working to maintain a state of biological balance.

The ECS regulates a plethora of physiological processes, including immune function and inflammation. Both CB1 and CB2 receptors can be found on immune cells, although there are between 10-100 times more CB2 receptors than CB1. Endocannabinoids act upon immune cells directly through the CB2 receptor.

CB2 receptor activation creates an anti-inflammatory effect and is therefore a therapeutic target for autoimmune disorders and neurodegenerative disease.1 However, any ECS immunosuppressant activity is thought to be transient, and can be overridden when necessary in the presence of infection.2

Scientists know that plant cannabinoids like tetrahydrocannabinol (THC) and cannabidiol (CBD) impact our health by interacting in different ways with the endocannabinoid system. Thus, it makes sense that consuming medical cannabis will also directly affect our immune system. But researchers are struggling to understand exactly how.

Cannabis and the Immune System

When we talk about cannabis, we’re dealing with upwards of 400 different molecules. These include the more frequently studied cannabinoids like THC and CBD, more than 100 other minor cannabinoids, dozens of terpenes, and a host of flavonoids – the combination of which varies according to the cannabis strain.

While most work has been carried out on individual cannabinoids, in particular THC and CBD, if you’re looking for some solid conclusions about how they affect the immune system, think again.

THC has been the focus of the bulk of research. THC binds to the CB2 receptor and activates it, which has an anti-inflammatory effect. This suggests that THC is immunosuppressant. Accordingly, THC is thought to show promise for autoimmune diseases, such as Crohn’s and multiple sclerosis. CBD, despite little binding affinity with cannabinoid receptors, is also considered to be immunosuppressant, reducing cytokine production3 and inhibiting T-cell function4.

But that’s only part of the story. A new wave of research and mounting anecdotal evidence points towards cannabinoids having an adaptive, immunomodulating effect, rather than just suppressing immune activity.

Cannabis and HIV

Medical cannabis is a well-established palliative treatment for HIV thanks to the plant’s ability to reduce anxiety, improve appetite, and ease pain. But recent research takes THC’s role even further, suggesting that it can actually upregulate the immune system, potentially improving patient outcomes.

Initially, preclinical research had corroborated the view that THC was immunosuppressant in HIV, increasing viral load and worsening the disease.5 More recent research, however, has suggested immune-stimulating effects.

A 2011 study by Lousiana State University scientists revealed astonishing results when monkeys were given THC over 28 days prior to SIV infection (the simian version of the virus). THC appeared to have some kind of protective effect, lengthening the lives of the monkeys and reducing viral load.6

Additional research by the same team in 2014 took these findings one step further. This time monkeys were given THC for a period of seventeen months before SIV infection. Not only was there an increase in T-cells and a reduction in viral load, but THC appeared to have protected the monkeys against the intestinal damage commonly caused by the virus.7

These exciting results have also been replicated in humans. In a study conducted by researchers at universities in Virginia and Florida, CD4 and CD8 white blood cell counts were compared in a sample of 95 HIV patients, some of whom were chronic cannabis users.8 Scientists discovered that both types of infection-fighting immune counts were higher in patients using cannabis, suggesting their immune systems had been bolstered by the plant.

Cannabis, Cancer, and the Immune System

Cancer will affect one in two of us at some point in our lifetime. There’s no hard and fast rule why it appears, but most cancers share the same mechanism.

Our immune system is primed to spot rogue cells and, through mechanisms such as apoptosis, eliminate any that might become tumors. Unfortunately, cancer cells can outwit our immune system by getting it to work in their favour.

Esther Martinez, a cannabinoid research scientist at Madrid’s Complutense University, describes a kind of crosstalk between cancer cells and the immune system. “When the tumor talks with immune cells, it reverses the signal,” she told Project CBD. “So, it’s like, ‘I’m here, and now I want you to work for me.’ And instead of attacking the tumor, it gives pro-survival signals, so the immune system around the cancer goes through a change. The tumors have the capacity to shut off the immune system.”


Cannabis oil, fresh cannabis flower, and a pink ribbon on a white background.

With the immune system unarmed, cancer cells grow uncontrollably. Until recently, the only approved anticancer weapons have been treatments like chemotherapy, which destroy not just the cancer cells, but also fast-growing, healthy cells.

It’s no surprise, then, that tremendous excitement lies around the antitumoral properties of the cannabis plant, in particular THC and CBD. In fact, it was Esther’s colleagues at the Complutense University, Manuel Guzman and Cristina Sanchez, who paved the way in investigating the cancer-killing effects of cannabinoids, primarily, but not exclusively through apoptosis.9

However, very little is known about the relationship between the immune system and cannabinoids in this process. One reason is that in many preclinical trials, human tumors grafted onto immunosuppressed mice are used to avoid rejection by their rodent hosts.

Some studies do exist using immune competent mice, such as Dr Wai Liu’s 2014 report, which examined the effects of THC and CBD on brain tumors when combined with radiotherapy. Not only were the tumors significantly reduced, but little if no immune suppression was witnessed in the study, according to Dr Liu, a London-based Research Fellow and cannabinoid Scientist.10

This is welcome news, as cannabinoids can also cause apoptosis in lymphocyte cells, potentially suppressing the immune system. The ability of cannabinoids to both suppress and bolster immune function lends credence to the idea that the endocannabinoid system is involved in immunomodulation, as Dr. Liu told Project CBD: “I suspect that cannabinoids are having a double-punch effect of 1) direct killing and 2) enhancing immunity by suppressing those immune cells that serve to hold back the immune-based killing cells.”

Immunotherapy for Cancer

Uncertainty about the interaction between cannabinoids and the immune system raises doubts regarding the use of medical cannabis during immunotherapy. Proclaimed the wonder cancer treatment of the future, immunotherapy retrains white blood cells to detect and kill cancer in the body. Thus far, however, there has only been one study examining how cannabinoids may affect this process – and the results were problematic.

Conducted at the Rambam Medical Centre in Haifa, Israel, patients taking medical cannabis alongside the immunotherapy cancer drug Nivolumab responded 50% less compared to those on immunotherapy alone.11 Curiously, subjects taking medical cannabis high in THC responded better to immunotherapy than those on a low strength THC product. No significant change in overall survival rates for patients was noted.

There are also anecdotal reports from California cancer patients who maintain that they benefited by combining immunotherapy with a low-dose, CBD-rich cannabis oil regimen under a doctor’s supervision. In addition, a small but growing body of preclinical data suggests that combining CBD and THC with conventional chemotherapy and radiation could have a powerful synergistic effect as an anticancer treatment. But these findings have not been replicated in human trials.

Despite a lack of clarity regarding cannabinoids and immunotherapy, the preponderance of scientific data suggests that it’s time to abandon the antiquated and misleading immunosuppressant label and embrace the idea that cannabinoids are bidirectional immunomodulators. This is what Dr. Mariano Garcia de Palau, a Spanish cannabis clinician and member of the Spanish Medical Cannabis Observatory, has seen in his practice.

“I believe [cannabis] is immunosuppressive when there is hyper-immune response,” says Dr. Garcia de Palau, “but otherwise it regulates and corrects the immune system. In fact, you could say it functions like the endocannabinoid system, bringing equilibrium to the organism.”

What does this mean in practical terms if you regularly use cannabis, have a compromised immune system or are starting immunotherapy? Where possible consult with your medical practitioner. In the meantime, we can only hope that more research will shed light on the complex relationship between the endocannabinoid system, our immune response, and compounds in the cannabis plant.

Mary Biles is a journalist, blogger and educator with a background in holistic health. Based between the UK and Spain, she is committed to accurately reporting advances in medical cannabis research. This is her first article for Project CBD.


1. Caroline Turcotte, Marie-Renee Blanchet, Michel Laviolette, and Nicolas Flamand. The CB2 receptor and its role as a regulator of inflammation. Cellular and Molecular Life Sciences. 2016; 73(23): 4449-4470. doi: 10.1007/s00018-016-2300-4
2. Rupal Pandey, Khalida Mousawy, Mitzi Nagarkatti, and Prakash Nagarkatti. Endocannabinoids and immune regulation. Pharmacol Res. 2009 Aug; 60(2): 85-92, doi: 10.1016/j.phrs.2009.03.019
3. Francieli Vuolo, Fabricia Petronilho, Beatriz Sonai, Cristiane Ritter, Jaime E. C. Hallak, Antonio Waldo Zuardi, Jose A. Crippa, and Felipe Dal-Pizzol. Evaluation of Serum Cytokines Levels and the Role of Cannabidiol Treatment in Animal Model of Asthma. Mediators of Inflammation. 2015; 2015: 538670. doi: 10.1155/2015/538670
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6. Patricia E. Molina Peter Winsauer Ping Zhang Edith Walker Leslie Birke Angela Amedee Curtis Vande Stouwe Dana Troxclair Robin McGoey Kurt Varner Lauri Byerley Lynn LaMotte. Cannabinoid Administration Attenuates the Progression of Simian Immunodeficiency Virus. AIDS Research and Human Retroviruses Vol. 27, No. 6.
7. Patricia E. Molina,Angela M. Amedee, Nicole J. LeCapitaine, Jovanny Zabaleta, Mahesh Mohan, Peter J. Winsauer, Curtis Vande Stouwe, Robin R. McGoey, Matthew W. Auten, Lynn LaMotte, Lawrance C. Chandra, and Leslie L. Birke. Modulation of Gut-Specific Mechanisms by Chronic ?9-Tetrahydrocannabinol Administration in Male Rhesus Macaques Infected with Simian Immunodeficiency Virus: A Systems Biology Analysis. AIDS Res Hum Retroviruses. 2014 Jun 1; 30(6): 567-578. doi: 10.1089/aid.2013.0182
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9. Guzman M. M J Duarte, C Blazquez, J Ravina, M C Rosa, I Galve-Roperh, C Sanchez, G Velasco, and L Gonzalez-Feria. A pilot clinical study of ?9-tetrahydrocannabinol in patients with recurrent glioblastoma multiforme. Br J Cancer. 2006 Jul 17; 95(2): 197-203. doi: 10.1038/sj.bjc.6603236
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Copyright, Project CBD. May not be reprinted without permission.

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