Last verified: April 2026

The MacCallum & Russo Protocol

The most widely cited evidence-based dosing protocol comes from MacCallum and Russo (2018, European Journal of Internal Medicine). Their recommendations, drawn from clinical trial data and pharmacokinetic principles, establish a framework that has become the de facto standard for cannabis-literate clinicians.

The protocol specifies: begin at 2.5 mg THC once daily, preferably in the evening to minimize daytime impairment. Increase by 2.5 mg every two days until therapeutic benefit is achieved or side effects emerge. The recommended maintenance ceiling is 15 mg/day for most patients. Beyond 20–30 mg/day, adverse effects — anxiety, cognitive impairment, tachycardia — increase without proportional gains in efficacy.

Doses above 20–30 mg/day of THC are associated with increased adverse events without additional therapeutic benefit in most patients.

MacCallum & Russo, European Journal of Internal Medicine 2018

This protocol contradicts the common consumer pattern of escalating doses to overcome tolerance. The pharmacological rationale is that THC is a partial agonist at CB1 receptors with a biphasic dose-response curve — low doses produce anxiolysis and analgesia, while high doses can paradoxically increase anxiety and pain sensitivity. More is not more.

CBD Dosing — Condition-Specific Ranges

CBD dosing varies dramatically by indication, spanning nearly three orders of magnitude. The evidence base supports distinct ranges for different conditions:

Epilepsy (Epidiolex label): 5–20 mg/kg/day in divided doses. For a 70 kg adult, this translates to 350–1,400 mg/day — pharmaceutical-grade doses that bear no resemblance to over-the-counter CBD products typically dosed at 10–50 mg. The Epidiolex pivotal trials used purified CBD under medical supervision with regular liver function monitoring, making direct extrapolation to consumer products scientifically inappropriate.

Anxiety (Linares et al. 2019): The key finding is an inverted U-shaped dose-response curve. In a simulated public speaking test, 300 mg CBD significantly reduced anxiety compared to placebo, but neither 150 mg nor 600 mg showed statistically significant effects. This bell-curve response means that both under-dosing and over-dosing miss the therapeutic window — a pattern inconsistent with the "more is better" assumption driving consumer behavior.

The inverted-U finding has been replicated in anxiety-adjacent models and is consistent with CBD's complex pharmacology: at different concentrations, CBD acts through different receptor systems (5-HT1A at lower concentrations, TRPV1 desensitization at higher concentrations), producing qualitatively different downstream effects.

Ratio Products — CBD:THC Combinations

Ratio products represent an increasingly important category in clinical cannabinoid therapy. The rationale rests on CBD's ability to modulate THC's effects through negative allosteric modulation of the CB1 receptor — CBD does not directly block THC binding but changes the receptor's conformation, reducing THC's efficacy and potency at a given concentration.

20:1 CBD:THC — Primarily CBD-driven effects with minimal psychoactivity. Used clinically for anxiety, inflammation, and conditions where THC is either unnecessary or contraindicated. The small THC component may contribute sub-threshold entourage effects without producing impairment. This ratio is often the starting point for cannabis-naive patients and pediatric applications.

1:1 CBD:THC — The ratio used in Sativex (nabiximols), the most extensively studied cannabinoid pharmaceutical, approved in over 29 countries for MS spasticity and cancer pain. The balanced ratio exploits CBD's ability to mitigate THC-induced anxiety and tachycardia while preserving THC's analgesic and muscle-relaxant properties. Clinical trial data from the Sativex program demonstrates that 1:1 ratios produce fewer psychoactive side effects than equivalent doses of THC alone.

THC-dominant ratios — Used for conditions where THC is the primary therapeutic agent: appetite stimulation (cancer cachexia, HIV wasting), sleep (THC's sedative effects at moderate doses), and nausea (antiemetic action via brainstem CB1 receptors). For sleep specifically, clinicians often recommend evening-only dosing to leverage THC's sleep-onset properties while minimizing daytime cognitive effects.

Microdosing — The Sub-Therapeutic Hypothesis

Microdosing cannabis — typically 2.5–5 mg THC — has gained attention as a strategy to achieve therapeutic benefits below the threshold of intoxication. The pharmacological rationale is grounded in THC's biphasic dose-response: at very low doses, anxiolytic, analgesic, and anti-inflammatory effects may occur without the cognitive impairment, tachycardia, and anxiety that emerge at higher doses.

Preliminary evidence supports the concept. Portenoy et al. (2012) found that cancer patients receiving low-dose nabiximols (1–4 sprays/day, approximately 2.7–10.8 mg THC) reported statistically significant pain reduction compared to placebo, while those receiving high doses (11–16 sprays/day) did not differ from placebo and reported significantly more adverse events. This finding — better outcomes at lower doses — directly supports the microdosing framework.

The practical challenge is that commercial products are often dosed at 5–10 mg minimum, making sub-5 mg dosing difficult without products specifically designed for microdosing. Some jurisdictions now mandate 2.5 mg single-serving options, improving access to low-dose strategies.

The Inverted-U Problem

The inverted-U dose-response relationship recurs across cannabinoid pharmacology and represents one of the most important — and most frequently ignored — principles in cannabis therapeutics. THC produces anxiolysis at low doses and anxiogenesis at high doses (Childs et al. 2017). CBD reduces anxiety at 300 mg but not at 150 mg or 600 mg (Linares et al. 2019). Whole-plant extracts show non-linear dose-response curves (Gallily et al. 2015).

The mechanism varies by compound and target. For THC at CB1, it reflects partial agonism: at low receptor occupancy, the signal is pro-homeostatic; at high occupancy, compensatory mechanisms (receptor internalization, beta-arrestin recruitment) shift the net effect. For CBD, the inverted-U likely reflects dose-dependent shifts between receptor targets — low-dose 5-HT1A agonism versus high-dose TRPV1 desensitization producing opposing downstream effects on anxiety circuits.

The clinical implication is profound: dose escalation can move a patient past the therapeutic window, not toward it. A patient who "needs more" may actually need less. This is counterintuitive to both patients and clinicians trained on conventional pharmaceuticals with monotonic dose-response relationships, and it is arguably the single most important concept in cannabis dosing science.

Practical Dosing Framework

Synthesizing the evidence, an evidence-based dosing approach includes: (1) Start at 2.5 mg THC or a high-CBD ratio product. (2) Increase by no more than 2.5 mg every 48 hours. (3) Recognize that optimal dose may be lower than expected. (4) If increasing dose produces diminishing returns, consider decreasing rather than escalating. (5) Match route of administration to clinical need — inhalation for acute symptoms, oral for sustained relief. (6) Monitor for the inverted-U phenomenon and educate patients that more is not necessarily better.

The gap between this evidence-based framework and typical consumer behavior — where products containing 50–100 mg THC are common and escalating doses are normalized — represents one of the largest disconnects in cannabis medicine.