This study investigated the effects of CBD on subjective responses to self-paced endurance exercise in recreationally active individuals. Contrary to our hypothesis, it showed that CBD (150 mg, oral) did not alter affective valence during or following exercise (i.e., a ∼ 10 km run). Other subjective feelings (i.e., enjoyment, motivation, self-efficacy, euphoria, pain, anxiety, sedation) were likewise unchanged.

Two previous studies have investigated the effects of CBD on subjective responses to exercise [6, 29]. Both found that CBD increased positive affect. However, one [6] was unblinded and co-administered a low, but not negligible, dose of THC (∼ 4 mg). The other [29] used: (1) a 300 mg dose of CBD; (2) a fixed-intensity treadmill run; and (3) an endurance-trained population. These methodological features likely increased its sensitivity (i.e., to change) compared to the current investigation, which used a lower 150 mg dose, self-paced outdoor run, and recreationally active population. However, they also limit the study’s ecological validity. Indeed, while doses ≥ 300 mg have demonstrated more consistent therapeutic effects [11], they are less readily available [11, 12]. Likewise, although fixed-intensity exercise produces less varied/noisy responses, endurance exercise is often self-paced. (The endurance-trained population is also much smaller than the recreationally active one). Put simply, our findings suggest that the subjective effects of CBD observed in prior studies [6, 29] might not be sustained under typical ‘real-world’ conditions. Further research is required to determine if CBD is efficacious, and if so, which condition/s (e.g., dose, ‘type’ of exercise, participant population) is/are moderating its effects.

Neither this study nor either of those published previously observed an effect of CBD on perceived exertion or ‘run time’ [6, 29]. This, along with the finding that CBD does not compromise the subjective experience of exercise, suggests it is unlikely to impede physical activity participation, which is significant given its apparent popularity [50]. Indeed, CBD use (e.g., for medicinal and/or ‘wellness’ purposes) has become common in North America and Europe where products can be purchased online and over-the-counter [11, 12]. Two recent randomised, placebo-controlled trials [51, 52] likewise found no effect of chronic CBD use on physical activity participation in healthy free-living adults – albeit at very low doses (10 and 50 mg/day).

Finally, it is worthwhile noting that, although well-established [53], this study elegantly demonstrates the powerful mood-enhancing effects of exercise. Indeed, despite inducing negative affect and pain, the 10 km runs, once completed, increased positive affect, and decreased negative affect and anxiety: effects that have previously been attributed, in part, to endogenous cannabinoids (e.g., anandamide) [53].

One strength this study has over others in its field [5, 6, 29] is that it was able to investigate the effects of CBD in the presence (on average) of negative affect (i.e., negative rather than positive FS ratings; see Table 2). A second strength is that it measured affect during (not just following, e.g. [5]), exercise. Indeed, ‘in-exercise’ measures more reliably predict future physical activity participation [54, 55].

This study is, however, limited in several aspects:

First, no physiological or biochemical (e.g., plasma CBD concentration) measures were taken. Indeed, these were impractical to obtain ‘en masse’. The few studies that have investigated the effects of CBD on exercise physiology suggest it has either no effect (∼ 13.6 mg, inhaled) [56] or a ‘possible’ effect to increase VO₂ and VO_2max (300 mg, oral) [29] at fixed-intensities. The pharmacokinetics of the soft-gel capsules used in this investigation have been characterised (by the supplier) [57] – but not yet publicly disclosed.

Second, no habituation session was conducted. Indeed, we were concerned that the addition of a third 10 km run might deter some individuals (particularly those most likely to experience negative affect during exercise) from participating. In the end, however, only one outcome measure (i.e., negative affect) demonstrated a significant main effect of Run (i.e., trial order) – and this was handled analytically.

Third, we were unable to standardise menstrual phase. That said, there is relatively limited evidence that menstrual phase influences subjective responses to exercise (i.e., the effects reported to date appear inconsistent and sporadic) [58–60]. It should also be noted that the current investigation was designed to determine whether the subjective effects of CBD observed in prior studies were sustained under more ecologically valid conditions; that is, in the presence of ‘real-world’ factors such as this.

Fourth, participants could have used external CBD in the 7 days preceding Run 1, and/or between Run 1 and Run 2, as abstinence was only verified 24 h prior to each treatment session. That said, as: (1) only four participants (∼ 8%) had ever tried CBD (Table 1); (2) none had used it in the last 3 months (Table 1); and (3) CBD cannot (yet) be accessed without a prescription in Australia [12], this seems reasonably unlikely.

Fifth, running pace was not measured. This could have been altered, even though total run time was not.

Finally, it should be noted that although synthetic -(-) CBD is chemically identical to plant-derived CBD, plant-derived CBD products often contain additional cannabinoids and cannabis constituents that are lacking in synthetic ones (such as ours). These constituents are usually only present in low concentrations. However, their inclusion does mean that plant-derived CBD products have the potential to produce slightly different effects [61].