Medical Cannabis Dosage Guide for UK Patients

Starting medical cannabis safely in the UK means understanding how to find the right dose for your body, your condition and your chosen product format. Unlike many pharmaceutical medicines, there is no single standard dose — titration (gradually adjusting up) is the gold standard recommended by UK specialists and endorsed by Project TWENTY21 guidance.

Starting Doses and the Titration Method

The universally accepted principle in UK medical cannabis prescribing is "start low, go slow". For flower vaporised in a Volcano or similar medical-grade device, a typical starting dose is 0.05–0.1 g per session, once or twice daily. For oil administered sublingually, a starting dose of 1–2.5 mg THC (or CBD) once daily in the evening is standard. Your prescribing clinician — who must be a GMC-registered specialist — will review your response at 4–6 weeks and adjust accordingly.

Titration typically follows this pattern for THC-containing products:

• Week 1–2: Minimum dose, evening only, to assess tolerance and sleep effects
• Week 3–4: Increase by 1 mg THC per dose if well tolerated, add daytime dose if needed
• Week 5+: Continue incremental increases of 1–2 mg every two weeks until therapeutic effect is achieved or side-effects occur
• Target range: Most UK patients stabilise between 10–30 mg THC/day total; some conditions (severe neuropathic pain) require higher doses under specialist supervision

CBD-only products require less caution but still benefit from titration — typical starting doses are 10–25 mg CBD twice daily, increasing weekly by 10–25 mg until relief is experienced.

Flower vs Oil Dosing — Key Differences

The bioavailability of inhaled (vaporised) cannabis is 30–50%, meaning a significant portion of cannabinoids reaches the bloodstream. Onset is rapid: 5–15 minutes. This makes vaporised flower suitable for breakthrough pain or acute anxiety but harder to dose precisely.

Oils taken sublingually have 20–35% bioavailability with onset at 30–90 minutes. They are more predictable for consistent dosing throughout the day. Patients with chronic pain often use a combination: a morning oil dose for background relief and flower for breakthrough episodes.

For capsules, bioavailability drops to 6–20% due to first-pass liver metabolism, but duration is longest (4–8 hours). Capsules suit patients who need stable daytime relief without repeated dosing.

THC:CBD ratios matter significantly. A 1:1 ratio (equal THC and CBD) is the most prescribed starting point in the UK for pain and inflammation — the CBD moderates some of the psychoactive effects of THC. High-CBD, low-THC products (e.g. 1:20 THC:CBD) are used for anxiety, epilepsy and patients sensitive to THC's psychoactive properties.

Vaporiser Temperatures and Doctor Guidance

For patients using a dry herb vaporiser, temperature directly affects which compounds are released. MHRA-licensed clinics and Project TWENTY21 researchers recommend:

• 160–170°C: Primarily CBD and terpenes — calming, minimal psychoactivity, suitable for daytime use
• 175–185°C: Full THC activation alongside CBD — standard therapeutic range for most conditions
• 190–200°C: Higher THC intensity, some CBN release — used for severe pain or insomnia under specialist guidance
• Above 200°C: Combustion risk increases; not recommended for medical use

Always store prescribed flower in its original packaging until use. Do not mix strains in a single session unless specifically discussed with your prescriber, as the combined cannabinoid and terpene profile may differ from your assessed dose. If you are unsure about your current regime, request a medication review from your UK medical cannabis clinic — most offer these as part of the standard follow-up schedule.