Are side effects of cannabidiol (CBD) products caused by tetrahydrocannabinol (THC) contamination?

CBD degradation

To investigate CBD degradation, differently concentrated CBD in methanolic solutions was used in a range corresponding to typical amounts consumed with supplements based on commercial CBD (Supelco Cerilliant #C-045, 1.0 mg/mL in methanol) supplied by Merck (Darmstadt, Germany). These solutions were exposed to an artificial gastric juice as well as different incubation times and stress factors such as storage under light and heat (see Table 1 for full experimental design). The solutions were stored either in standard freezer (-18°C) or refrigerator (8°C) or at room temperature (20°C). Increased temperatures were achieved using a thermostatically controlled laboratory drying oven type “UT6120” (Heraeus, Langenselbold, Germany) set to either 37°C or 60°C. The daylight condition was achieved by storage at a window (south side). For ultraviolet light exposure, six 25 W ultraviolet (UV) fluorescent tubes type “excellent E” (99.1% UVA) built into a facial tanner type “NT 446 U” (Dr. Kern GmbH, Mademühlen, Germany) were placed 15 cm from the surface of the solutions. In deviation of an experimental protocol of Merrick et al.¹¹, a gastric juice without addition of surfactants was used, which was strictly produced according to the European pharmacopoeia¹² (0.020 g NaCl + 0.032 g pepsin + 0.8 mL HCl (1 mol/L), filled up to 10 mL with water). As pure CBD was available only in methanolic solution, the final experimental setups contained 0.08 mol/L HCl and 1% methanol due to dilution.

The samples were measured using a triple quadrupole mass spectrometer (TSQ Vantage, Thermo Fisher Scientific, San Jose, CA, USA) coupled with an LC system (1100 series, Agilent, Waldbronn, Germany) and also using a quadrupole time-of-flight (QTOF) mass spectrometer (X500, Sciex, Darmstadt, Germany) coupled with an UPLC system (1290 series, Agilent, Waldbronn, Germany). Both systems used the same separation column (Luna Omega Polar C18, 150 × 2.1 mm, 1.6 µm, 100 Å, Phenomenex, Aschaffenburg, Germany). The separation was isocratic with 25 % formic acid (0.1 %) and 75 % formic acid (0.1 % in acetonitrile) and a flow of 0.3 mL/min. In case of QTOF with 35 % formic acid (0.1 %) and 65 % formic acid (0.1 % in acetonitrile) and a flow of 0.45 mL/min. The evaluation took place after fragmentation of the mother ion into three mass traces for each compound. As quantifier for ∆⁹-THC, ∆⁸-THC and CBD, the mass transition m/z 315 to 193 was used, for cannabinol (CBN) m/z 311 to 223, and for tetrahydrocannabinolic acid (THCA) m/z 359 to 341. For ∆⁹-THC and ∆⁸-THC, baseline separation was achieved. In case of QTOF, quantification was conducted over accurate mass and control of fragmentation pattern. CBD eluted as one of the first cannabinoids, a few minutes before ∆⁹-THC and ∆⁸-THC. As internal standards ∆⁹-THC-D₃ (Supelco Cerilliant #T-011, 1.0 mg/mL in methanol) was used for the quantification of ∆⁹-THC (Supelco Cerilliant #T-005, 1.0 mg/mL in methanol), THCA (Supelco Cerilliant #T-093, 1.0 mg/mL in acetonitrile) and CBN (Supelco Cerilliant #C-046, 1.0 mg/mL in methanol), and cannabidiol-D₃ (Supelco Cerilliant #C-084, 100 µg/mL in methanol) for quantification of CBD (Supelco Cerilliant #C-045, 1.0 mg/mL in methanol). The certified reference materials were obtained as solutions in ampoules of 1 mL, all supplied by Merck (Darmstadt, Germany). A limit of detection (LOD) of 5 ng/mL was determined. For both procedures, relative standard deviations better than 5% were achieved.

THC contamination of commercial products

To study the possible influence of natively contained THC in hemp products as a cause for side effects, a sampling of all available CBD products registered as food supplement in the German State Baden-Württemberg, other available hemp extract products in retail, as well as all products available at the warehouse of a large internet retailer were sampled between December 2018 and July 2019. A total of 28 samples (see Table 2 for product designations) were analyzed using the above described liquid chromatographic method with tandem mass spectrometry (LC-MS/MS) for THC content. For toxicological evaluation of the results, the lowest observed adverse effect level (LOAEL) of 2.5 mg THC per day published by the European food safety authority (EFSA) based on human data (central nervous system effects and pulse increase) was used¹⁵. Taking safety factors (factor 3 for extrapolation from LOAEL to no observed adverse effect level (NOAEL) and factor 10 for interindividual differences, total factor 30) into account, an acute reference dose (ARfD) of 1 μg THC per kg body weight was derived¹⁵.

Direct pharmacological effect of CBD as explanation of side effects

There is not much evidence to assume that chemically pure CBD may exhibit THC-like side-effects. The World Health Organization (WHO) judged the compound as being well tolerated with a good safety profile³ and the CBD doses in the food supplements on the market are typically much lower than the ones tested in clinical studies. Additionally, there is a 90-day experiment in rats with a hemp extract (consisting of 26% cannabinoids, 96% CBD and <1% THC) from which a NOAEL of 100 mg/kg bw/day could be derived¹⁶. For CBD this would be about 25 mg/kg bw/day (or 1750 mg/day for a person with a body weight of 70 kg). This NOAEL would not be reached by the CBD dosages in food supplements.

CBD conversion into THC as explanation of side effects

Some, partly older, in vitro studies put up hypotheses about the conversion of CBD to THC under acidic conditions such as in artificial gastric juice^11,17–19. If these proposals could be confirmed with in vivo data, consumers taking CBD orally could be exposed to such high THC levels that the threshold for pharmacological action could be exceeded²⁰. However, taking a closer look at these in vitro studies raises some doubts. If CBD was to be converted to THC in the stomach, typical THC metabolites should be detectable in blood and urine, but this has not been observed in oral CBD studies^21,22. Due to the contradicting results, a replication of the in vitro study of Merrick et al.¹¹ was conducted using an extended experimental design. A more selective LC-MS/MS method and also an ultra-high pressure liquid chromatographic method with quadrupole time-of-flight mass spectrometry (UPLC-QTOF) were used to investigate the CBD degradation.

Under these conditions in contrast to Merrick et al.¹¹, no conversion of CBD to THC was observed in any of the samples. Only in case of the positive control (2 week storage in 0.5 mol/L HCl and 50% methanol), a complete degradation of CBD into 27% THC and other not identified products (with fragments similar to the ones found in CBN and THC fragmentations but with other retention times) was observed (Table 1, underlying data¹³). From an analytical viewpoint, the use of less selective and specific analytical methods, especially from the point of chromatographic separation, could result in a situation in which certain CBD degradation products might easily be confused with THC due to structural similarities. Thus, similar fragmentation patterns and potentially overlapping peaks under certain chromatographic conditions might have led to false positive results in the previous studies. In conclusion of our degradation experiments, we agree with more recent literature^23,24 that CBD would not likely react to THC under in vivo conditions. The only detectable influence leading to degradation is strong acidity, which should be avoided in CBD formulations to ensure stability of products.

THC contamination as cause of side effects

Out of 28 samples, 10 samples (36% of the collective) were exceeding the THC LOAEL and were assessed as harmful to health. 14 samples (50% of the collective) were classified as unsuitable for human consumption due to exceeding the ARfD (see Table 2, underlying data¹³). Furthermore, all samples (100%) have been classified as non-compliant to Regulation (EU) 2015/2283 of the European Parliament and of the Council of 25 November 2015 on novel foods²⁵ and therefore being unauthorized novel foods. The labelling of 28 samples (100%) was also non-compliant to Regulation (EU) No 1169/2011 of the European Parliament and of the Council of 25 October 2011 on the provision of food information to consumers²⁶, e.g. due to lack of mandatory food information such as ingredients list or use of unapproved health claims in accordance to Regulation (EC) No 1924/2006 of the European Parliament and of the Council of 20 December 2006 on nutrition and health claims made on foods²⁷. In summary, none of the products in our survey was found as being fully compliant with European food regulations.

The THC dose leading to intoxication is considered to be 10 to 20 mg (very high dose up to 60 mg) for inhalatory intake²⁸. The resorption of orally ingested THC varies greatly interindividually with respect to both total amount and resorption rate²⁹. This might be one of the reasons for the individually very different psychotropic effects. A single oral dose of 20 mg THC resulted in symptoms such as tachycardia, conjunctival irritation, “high sensation” or dysphoria in adults within one to four hours. In one in five adults, a single dose of 5 mg already showed corresponding symptoms³⁰.

Some of the CBD oil supplements contained THC in doses up to 30 mg, which can easily explain the adverse effects observed by some consumers. Most of the CBD oils with dosage of around 1 mg offer the possibility to achieve intoxicating dosages of THC if the products are used off-label (i.e. increase of the labelled maximal dosage by factors of 3–5, which is probably not an unlikely scenario). Generally, in the current purity, the CBD products achieve an insufficient margin of safety, especially in light of the German guidance value for THC in food products^14,31, which is 150 µg/kg, a magnitude below the actual contents in the products.

Hence our results provide compelling evidence that THC natively contained in CBD products by contamination may be a direct cause for side effects of these products. Obviously, there is an involuntary or deliberate lack of quality control of CBD products. Claims of “THC-free”, used by most manufacturers, even of the highly contaminated products, have to be treated as fraudulent or deceptive food information.

Underlying data

Open Science Framework: Dataset for “Are side effects of cannabidiol (CBD) products caused by delta9-tetrahydrocannabinol (THC) contamination?” https://doi.org/10.17605/OSF.IO/F7ZXY¹³

This project contains the following underlying data:

Data are available under the terms of the Creative Commons Zero “No rights reserved” data waiver (CC0 1.0 Public domain dedication).