The UK pathway, stage by stage.

Is it legal to prescribe cannabis-based medicines in the UK?

Yes. On 1 November 2018 the UK moved cannabis-based products for medicinal use into a legal category that allows them to be prescribed. Only a doctor on the General Medical Council's Specialist Register can start a prescription. A GP can't, though a GP can take over ongoing prescribing under a shared-care arrangement once a specialist has started it. NHS prescriptions exist but are very rare, so nearly everyone in the UK who takes a cannabis-based medicine gets it privately. Most of the products are unlicensed. That's legal, but it means the prescriber takes on more responsibility for the decision, and the clinic has to show it's doing that carefully. That last sentence is why everything below exists.

These rules apply in Scotland too. For the Scottish detail, read Medical cannabis in Scotland: how it works.

Stage I. Referral and screening

Almost everyone starts by contacting a clinic themselves, though GPs and specialists refer too. The clinic's first job is to check you're eligible and safe to see, and often that's a nurse's job. You'll be asked about:

• your diagnosis, and the treatments you've already tried
• your medical history, including your heart
• your mental health, and any history of psychosis in you or your family
• whether you're pregnant or breastfeeding
• your own history with cannabis.

Most clinics use a standard questionnaire for cannabis use, and a mental health screen, at this point.

You'll usually be asked for evidence of your diagnosis and treatment. A summary of your GP record is the norm, and the clinic will tell you how to get it. This stage can save everybody time. It works out whether someone is likely to be suitable before they pay for a consultation. And it gets the paperwork ready, so the doctor can make a decision.

Stage II. Specialist consultation

The consultation is with a specialist doctor whose specialty matches your condition: a pain consultant, a psychiatrist, a neurologist and so on. Expect twenty to forty-five minutes, nearly always by video. They'll take a full history and go through your records and the screening. They'll talk through what a cannabis-based medicine could and couldn't do for you. And they'll discuss risks, side effects, driving, work and cost. If they think it's appropriate, they'll propose a starting product and a plan.

Do ask questions. It helps to arrive with a list.

Stage III. Multidisciplinary review

Most of these medicines are unlicensed. So each new patient is usually discussed by a multidisciplinary team before the first prescription is written. That's a group of the clinic's specialists, with a pharmacist and often a nurse. The team confirms the diagnosis fits, the eligibility criteria are met, the risks have been considered and the plan is sensible. It's usually quick, and it's a valuable check.

Stage IV. Prescription and dispensing

The prescription is private, so you pay for it, and it goes to a specialist pharmacy that's licensed to handle these products. The pharmacy sources the medicine, checks the prescription, and dispenses it, almost always by tracked post to your door. You'll receive the medicine in its original packaging with your name on it. Keep that packaging: it matters for driving, work and travel.

Stage V. Follow-up and review

If a medicine is prescribed, the dose is usually adjusted over the first weeks, and nobody should be left to work that out alone. Clinics usually start on a low dose and increase slowly, with a review a few weeks in, then at regular intervals. This is where nurses come into their own. They check how you're getting on, adjust the plan with the prescriber, sort out side effects and deal with the practical questions. Outcomes are recorded, partly because it's good care and partly because good outcome data helps the whole field.

How long does it all take?

In my experience, it takes two to four weeks from first contact to the medicine arriving, if one is prescribed and your records come promptly. The consultation itself is usually available quickly. Any waits are usually for paperwork.

What usually goes wrong?

The common problems are practical ones: records that don't arrive, screening that's rushed, patients who aren't followed up, and driving law that nobody explained. None of them are hard to put right, and helping clinics do that is a large part of my work. If you're a patient, here are three useful questions for any clinic:

• Who screens me?
• Who reviews the decision?
• Who will I speak to after I start?