Inclusion Criteria:

Participants must meet the following criteria: 1. Diagnosed with MS (any subtype), for at least six months, by a MS neurologist, according to the recent version of the McDonald criteria; 2. Spasticity due to MS of at least one-month duration and not relieved with current therapy, at a level of 4 or more on the numerical rating scale (NRS); 3. Stable dose of standard therapies for at least 30 days prior to the screening visit and willingness for these to be maintained for the duration of the study; 4. Aged 21 years or older; 5. Ability (in the investigator's opinion) and willingness to comply with all study requirements; 6. Ability to speak and read French or English (grade-nine level of language required);

Exclusion Criteria:

Participants will be excluded if any of the following criteria are met: 1. Concomitant disease with symptoms of spasticity, or that may have influenced their level; 2. Received a botulinum toxin injection within four months prior to the screening visit or unwillingness to stop receiving botulinum toxin injections for the duration of the study; 3. Use of cannabis or cannabinoid-based medications within 7 days of study entry and unwillingness to abstain for the duration of the study; 4. History of schizophrenia, other psychotic illness or other significant psychiatric disorder other than anxiety or depression associated with their underlying condition; 5. Alcohol or substance use disorder other than nicotine; 6. History of epilepsy or recurrent seizures; 7. Hypersensitivity to cannabinoids or any of the excipients of the study medication; 8. Clinically relevant cardiac dysfunction within the last 12 months or had a cardiac disorder that, in the opinion of the investigator would put the subject at risk of a clinically relevant arrhythmia or myocardial infarction; 9. Impaired renal function i.e., serum creatinine clearance lower than 50 ml/min; 10. Significantly impaired hepatic function, at visit 1, in the investigator's opinion and/or had liver function tests of equal to or greater than three times the upper limit of normal; 11. Pregnancy or breastfeeding; 12. Men with history of fertility problems and who plan to conceive at any time in the future; 13. Any participant who plans to conceive either at screening or while enrolled in the study; 14. Inability (or unwillingness) of women of childbearing potential and men to use a medically acceptable form of contraception throughout the study duration; 15. Inability to use a medically acceptable form of contraception throughout the study duration; m) any other significant disease or disorder which, in the opinion of the investigator, may either put the subject at risk because of participation in the study, may influence the result of the study, or the subject's ability to participate in the study; 16. Intention to travel internationally, or to donate blood during the study.

The aim of this study is to document, 1. The efficacy of THC and CBD, alone and in combination, as add-on therapies to the current standard treatments for relief of spasticity and other symptoms in PwMS (muscle spasms and stiffness); 2. Assess the tolerability profile of THC and CBD, alone and in combination, when used in PwMS; 3. Identify the mechanisms underlying such therapeutic and adverse effects of different types of cannabis-based medicines in PwMS, Participants will initially receive THC 4mg/day or CBD 40mg/day or THC/CBD combination (THC 4mg and CBD 40mg/day), or placebo, on the first day. Dose will be increased up to 20mg (THC) and 200mg (CBD) per day, if well tolerated. Participants will receive the allocated treatment for a total of 4 weeks, followed by an additional 12 weeks of treatment for responders who will be identified as patients who had a decrease from baseline in spasticity of at least one point on the Numerical Rating Scale . THC and CBD will be taken as oil softgels in two divided doses per day. Cannabis extract and placebo will taste and look exactly the same. To protect from all contingencies and to minimize the risk of adverse reactions, the presence of adverse events will be evaluated at each research visit, as well as through courtesy calls between visits. If any mental or physical symptoms occur that require medical attention, the PwMS will be referred as required to an attending neurologist, psychiatrist, or other specialists .

Arms

Experimental: CBD alone

Dosage form : Softgel Dosage & frequency : 40 mg /day of CBD up to 200 mg in two doses a day Duration : 4 weeks of treatment followed by 12 additional weeks of follow up.

Experimental: THC alone

Dosage form : Softgel Dosage & frequency : 4 mg /day of THC up to 20 mg in two doses a day Duration : 4 weeks of treatment followed by 12 additional weeks of follow up.

Experimental: THC and CBD combined

Dosage form : Softgel Dosage & frequency : 40 mg /day of CBD up to 200 mg and 4 mg /day of THC up to 20 mg in two doses a day Duration : 4 weeks of treatment followed by 12 additional weeks of follow up.

Placebo Comparator: Placebo

Dosage form : Softgel Dosage & frequency : caps of placebo twice a day Duration : 4 weeks of treatment followed by 12 additional weeks of follow up.

Interventions

Drug: - Cannabis oil vs placebo

Eligibility, Screening and Baseline (T0): Candidates will be seen by both research staff and a neurologist. Full written informed consent will be obtained before completing questionnaires and administering physical and medical evaluations. If eligibility is confirmed, a blood sample will be collected followed by participant randomisation . Follow-up visits: Randomized participants come back after 4 weeks (T1) for the same assessments administered at T0. Only participants who had a decrease in their level of spasticity can continue their participation in the same allocated arm for an additional period of 12 weeks. At the end of the additional period of 12 weeks (T2), another visit is scheduled for a last assessments which are the same as T0 and T1. Throughout study, courtesy calls will be scheduled and standard care for MS will also be offered to ensure participants 'safety and well-being.