Eleven terpenes, four data states: why temperature tables are not comparable
We checked the boiling points of eleven terpenes of this cluster in the public PubChem database. Six have pressure given, one only a measurement in nearly vacuum, two a bare number, and two have no record at all.
| Data sheet | Measurement state |
|---|---|
| Terpenes with atmospheric measurement | 6 out of 11 |
| Terpenes only under reduced pressure | 1 out of 11 number not comparable to others |
| Terpenes without specified pressure | 4 out of 11 |
| Works in the evidence base | 2 |
- How much evidence. 2 works from 2022 to 2023, all listed in the table below along with the model.
- What has not been demonstrated. No study has been published measuring how much terpene from heated herb actually reaches the lungs and blood. It is known in what order the components evaporate and what portion decomposes along the way, but not in
- What you won’t find here. Dosage recommendations or strain indications. Selection is determined by the attending physician, and cannabis herb is a raw material issued only by prescription.
- How to read this. Results from rodent studies or cell cultures do not directly translate to a patient using herb, and the column with the model indicates what the work was actually about.
Does the number set on the vaporizer indicate how many degrees the herb has?
No. The display shows the temperature of the heating element or the air entering the chamber, not the temperature of the raw material itself. The plant material absorbs heat unevenly, and the airflow during inhalation takes some of that heat away. The difference between these two quantities certainly exists, although no one has publicly measured it.
This difference is the first of two reasons why the temperature table for terpenes does not translate to what happens in the device’s chamber. The number in the table describes the behavior of a pure substance in a laboratory vessel, the number on the display describes the state of the heater, and between the two lies plant material with its own uneven temperature. Even if the table were flawless, its column and the display would still describe two different measurement objects.
A separate text in this cluster breaks down this difference and shows why the vaporizer setting does not equal the temperature of the herb. Here, one statement suffices: no one has published a measurement indicating how much cooler the raw material is during a typical inhalation compared to the setting.
| Work | Model and route of administration | What was demonstrated |
|---|---|---|
| Zhu J et al., 2022 Scientific Reports PMID:35773373 |
laboratory measurement by thermal desorption coupled with gas chromatography and mass spectrometry, five monoterpenes at typical vaporization temperatures | Among the five studied monoterpenes, the proportion of the starting compound that survived heating unchanged ranged from 97 to 98 percent for the most resistant to just 11 to 28 percent for the most unstable. The most resistant was myrcene, the most unstable was terpinolene, and the difference between the extreme values is nearly ninefold. This is not a share in the profile, but the percentage of the substance that did not decompose, and the denominator here is the amount introduced into the measurement. The resulting oxidation products had molecular weights of 134, 150, or 152, among which p-(1-propenyl)-toluene, beta-pinene, and fenchol were likely identified. The authors note that the toxicity of inhaling these products is unknown, while allergic and irritating reactions to oxidized monoterpene oils are well documented. |
| Eyal AM et al., 2023 Cannabis and Cannabinoid Research PMID:35442765 |
analysis of own and literature data, review work with measurements of composition at various stages of processing | The authors reviewed documentation reaching patients and their caregivers and found erroneous data and confusion between the concepts of boiling, vaporization, and evaporation, including incorrectly stated boiling temperatures of cannabinoids. The rate of loss of individual components is determined by their relative vapor pressure at a given temperature, not the boiling point. Loss begins during drying and curing, intensifies during decarboxylation, with monoterpenes evaporating first. During vaporization, terpenes are inhaled before cannabinoids, and commercial cannabis products are poorer in terpenes, especially monoterpenes, than the plants from which they were derived. Terms like full spectrum are directly called misleading by the authors, as no product replicates the composition of the plant. |
Does a terpene start to evaporate only after exceeding the boiling point?
No. Molecules escape from the surface of the liquid at any temperature at which that liquid has any vapor pressure, which is practically always. Boiling only means that the vapor pressure has caught up with the surrounding pressure, and there is no switch at that moment. This misunderstanding underlies the entire idea of hitting a single terpene.
For this page, the consistency of this statement matters for the tables themselves. Since evaporation has no threshold, the column with boiling points is not a list of activation thresholds, but a list of values describing one narrowly defined physical situation. Which component escapes faster results from comparing vapor pressures at the same temperature, not from whether any number in the table has been exceeded.
Why do two temperature tables for terpenes provide different numbers?
Because the eleven terpenes of this project have four different data states in the public PubChem database, not one. Six have boiling points given along with pressure, one only a measurement under reduced pressure, two a bare number without any pressure, and two have no boiling point at all.
We conducted the verification ourselves, with one query to the public database interface for each terpene. With pressure given with the number are caryophyllene, limonene, linalool, myrcene, pinene, and terpinolene. Without specified pressure are nerolidol and ocimene. The records with boiling points are not held for bisabolol or farnesene: for both, the database responds with a message that such a position does not exist.
| Terpene | Database record | Pressure in record | Data state |
|---|---|---|---|
| pinene | 156 °C and 313.2 °F | 760 mm Hg | comparable record |
| myrcene | 166.0 to 167.0 °C and 332.6 °F | 760 mm Hg | comparable record |
| limonene | 352 °F, or 177.8 °C | 760 mm Hg | comparable record |
| terpinolene | 183.0 to 185.0 °C | 760 mm Hg | comparable record |
| linalool | 194.0 to 197.0 °C | 760 mm Hg | comparable record |
| caryophyllene | 256.0 to 259.0 °C | 760 mm Hg | comparable record |
| caryophyllene | 264 to 266 °F, or about 130 °C | 14 mm Hg | the same position under reduced pressure |
| humulene | 99.0 to 100.0 °C | 3 mm Hg | the only record, measurement in nearly vacuum |
| nerolidol | 275 to 277 °C | not specified | number cannot be compared to the above |
| ocimene | 177 °C | not specified | number cannot be compared to the above |
| bisabolol | no record | not applicable | database does not provide boiling point |
| farnesene | no record | not applicable | database does not provide boiling point |
These four states do not differ in degree of certainty, only in type of information. A number without pressure is not a worse measurement of the same quantity. It simply does not say under what conditions it was obtained, so it cannot be compared to the number given at 760 millimeters of mercury. Comparing them in one column creates an order that does not exist in the data.
This is also evident from the number of records themselves. Of the eleven terpenes, the database holds twenty-four source records from six different reference sets, and explicit pressure carries ten of them. Fourteen records, or the majority, do not state under what pressure they were obtained. A table constructed by taking the first better record from each terpene thus has a greater chance of hitting a value without conditions than a value with conditions.
Where does the number close to one hundred degrees for humulene come from in the tables?
From the only record that the database has for it. PubChem lists for humulene 99 to 100 degrees Celsius, but the measurement was made at a pressure of three millimeters of mercury, over two hundred fifty times lower than atmospheric. The database does not record any other value for this terpene.
Pressure shifts the boiling point by dozens of degrees and this is not a second-order correction. This is shown by caryophyllene, as the same position has two records in the database at once: 256.0 to 259.0 degrees at 760 millimeters of mercury and 264 to 266 degrees Fahrenheit at 14 millimeters of mercury, or about 130 degrees Celsius. Between one number and the other lies 127.5 degrees, and both describe the same substance.
The consequence for the table is arithmetic, not interpretive. A value from nearly vacuum placed in the column next to atmospheric values shifts humulene about 57 degrees below the lowest of them, meaning it should be read as a component that evaporates first. Meanwhile, humulene and caryophyllene are isomers with the same molecular weight, and caryophyllene stands highest in that column. Such a number is not a rounding or simplification, but a record of conditions that are no longer visible in the table.
Do records in one database agree with each other?
Not always. The same terpene may be described by several records from different reference sets, and these provide values that differ by several degrees. For linalool, the extreme records are separated by six degrees, for terpinolene by four. This is small compared to the difference resulting from pressure, but enough for two tables to appear contradictory.
Additionally, there is the conversion of units. Six out of twenty-four records are given in degrees Fahrenheit, and converting to Celsius gives a value with a decimal part, which usually disappears in tables due to rounding. The same position may also be listed twice, once in each scale, so counting records without checking their content could lead to taking one measurement as two independent ones.
None of these records is incorrect in its source. The error only arises when transcribing, when removing pressure, units, and range, and leaving only the number.
What does this mean for a person with a prescription for herb?
That the temperature table is not the basis for anything related to their own treatment. Cannabis herb is a pharmaceutical raw material issued by prescription in the Rpw category, so the method of administration is determined by the attending physician, not a compilation of numbers circulating online without a source.
This page does not provide any temperature as one that must be set, and has no intention of doing so. It describes the state of records in the public chemical database and what cannot be derived from those records. There is also no mention of equipment, as the selection of the device and method of taking the medication is a conversation with the attending physician, not the content of an informational article.
It is a separate matter that temperature compilations mainly revolve around products from general sales. The store cannabis herb category includes flowers of industrial hemp available without a prescription and is a different type of product than herb issued in pharmacies, although both may be described by the same table. We maintain a list of pharmaceutical strains to which this cluster pertains in the list of currently available strains.
What has not been studied about vaporizing terpenes from herb in humans?
The most important link, which is how much terpene from heated herb actually reaches the lungs and blood. The evidence base of this page has two positions: a review with its own measurements of composition and a laboratory measurement. None of them studies humans, so the chain from the number in the table to the effect on the patient breaks off along the way.
The second of these works is a measurement in the laboratory.
The greatest stability was shown by myrcene, the least by terpinolene, and the distance between the extreme positions is nearly ninefold. Among the decomposition products, molecules with masses of 134, 150, and 152 were recognized, one of which is likely fenchol. What inhaling such products does to a person has not been studied; however, what is well documented is that oxidized oils from this group can cause allergies and irritation.
Hence the conclusion that the tables do not carry. Even a record correct in terms of pressure and unit speaks of the behavior of a pure substance in a laboratory vessel, not of what reaches the vapor and what survives the journey unchanged.
Frequently asked questions
Does the boiling point of a terpene indicate at what temperature it will evaporate from herb?
No. The boiling point is the temperature at which the vapor pressure equals the surrounding pressure. Evaporation also occurs below this value, and its rate gradually increases, without an activation threshold.
Why do tables give a number close to one hundred degrees for humulene?
Because it is the only record that the public database has for this terpene, and it comes from a measurement at a pressure of three millimeters of mercury. When transcribed without pressure, it ends up in the column with atmospheric values, where it means something else.
What does the record 3 mm Hg at the boiling point mean?
That the measurement was made at a pressure about two hundred fifty times lower than atmospheric. Under such conditions, the substance boils significantly below the value it has in the air at ground level.
Is it known how much terpene from heated herb reaches the blood?
No study has been published measuring how much terpene from heated herb actually reaches the lungs and blood. It is known in what order the components evaporate and what portion decomposes along the way, but it is not known how much of this reaches the body or whether it has any measured effect. It has also not been demonstrated that setting the vaporizer to the temperature given in the table as the boiling point of a specific terpene leads to inhaling that particular terpene.
Where do the numbers in the table on this page come from?
From the public interface of the PubChem database, with one query for each terpene, along with the pressure record and the name of the reference set. The records are quoted in the form they stand in the database, without standardizing units.
Does this page provide a temperature for vaporization?
No. Cannabis herb is issued by prescription, and the method of administration is determined by the attending physician. The text describes the state of records in the chemical database, not the method of taking the medication.
The material is for informational purposes only and does not replace medical advice. Cannabis herb is a pharmaceutical raw material issued by prescription in the Rpw category. Editorial text by the ubucha.pl editorial team.
