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In February 2009, few months after the Beijing Summer Olympic Games, people around the world were shattered by the news when Michael Phelps, a 8-gold medalist in the Beijing Olympics admitted that he was smoking marijuana from a pong during a party.  Other than the renowned swimmer, there is no lack of celebrities who are caught using the drug illegally like Whitney Houston, James Brown and Oliver Stone, just to name a few.  In this 21st century, the use and legalization of marijuana is still a heated debate in most parts of the world despite the fact that its use can be traced back to thousands years ago. The people in China started using cannabis for medicinal purposes and as pain reliever about 4000 years ago. Later, the use of cannabis spread to other regions in India and Asia for religious use. 
What is marijuana?
According to Cambridge Online Dictionary, marijuana is a usually illegal drug made from the dried leaves and flowers of the hempÂ plant, which produces a feeling of pleasant relaxation if smoked or eaten.  The hemp plant is scientifically known as Cannabis sativa.  The active ingredient of cannabis is cannaboid. Tetrahydrocannabinol (THC), cannabidiol (CBD), cannabigerol (CBG), cannabinol (CBN), Cannabichromene (CBC), and olivetol are some of the natural cannabinoids that have been identified.  The main component that produces the psychoactive effect is THC while CBD is believed to have the inverse function by reducing the anxiety reaction induced. 
How does cannabinoid work in human body?
There is still no sufficient scientific evidence to show the mechanism of cannabinoids in our body but the identification and cloning of CB1 and CB2 receptors in year 1990 and 1993 respectively has hypothesised the presence of endocannabinoid system in our body.  CB1 receptors are found mostly in the central nervous system but are also present in the spinal cord, intestinal nervous system and gastrointestinal tract while CB2 receptors are located in peripheral nervous system. Endocannabinoid like anandamide is synthesised and released immediately at the post-synaptic neurons when stimulation is generated. They are not stored in vesicles like other neurotransmitters do. 
Therapeutic effects of marijuana
Multiple sclerosis (MS) is an autoimmune disease of the central nervous system in which the myelin sheaths of neurons are broken down by the immune system. Due to the damage of myelin sheaths, the transmission of signals in the body is disrupted thus affecting the actions of muscles. Symptoms shown are dependent on the areas affected such as muscles, bowel and bladder, eyes, digestive tracts and others.  Patients with MS usually suffer from intense muscle spasms. Spasticity is characterised by the involuntary and uncoordinated contractions of muscles which can occur in any parts of the body, especially legs.  According to the British Medical Association, patients with spastic neurological disorders finds that cannanabinoids shows better effects than other drugs available in market in relieving their distressing symptoms.  A survey involving 112 patients carried out in both USA and UK shows that cannabis improves their symptoms of MS with minimum negative effects reported. 
Sign or symptoms
Subjects with listed sign/symptom
Reactions reported after using cannabis
Showing improvement (%)
No changes (%)
Getting worse (%)
Spasticity at sleep onset
Pain in muscles
Spasticity when awaking in night
Pain in legs at night
Numbness of chest/ stomach
Figure 1: Adapted from effects of cannabis on MS signs and symptoms (all subjects) (Consroe et a l. 1997) 
About 7.5mg of THC administration is found to be effective in reducing muscular spasms.  SativexÂ® is a new synthetic drug consists of THC and CBD isolated from Cannabis Sativa L. which is taken sublingually. It is useful in the symptomatic relief of neuropathic pain in MS and is approved provisionally in Canada but the availability in Spain and UK is limited. 
Nausea and vomiting
Even though many antiemetic agents are developed over the decades, nausea and vomiting are still among other gruesome side effects which cancer patients experience after undergoing chemotherapy.  These symptoms are believed to be contributing to other negative emotions which will affect the mental strength of patients such as desperation and helplessness.  Double-blind and cross-over studies reveal that most patients prefer cannabis-based treatment to other control drugs (prochlorperazine, chlorpromazine, domperidone, halo-peridol, alizapride, metoclopramide, placebo) despite of the possible adverse effects.  This preference is possibly due to the low efficacy of other medications which is unable to ease their discomfort. There are 2 types of cannaboid-containing drug available for treating nausea and vomiting in cancer patients which are dronabinol (Marinol) and nabilone (CesametÂ®). Dronabinol is a synthetic of THC and has been approved by the Food and Drug Administration (FDA) in April 2003. Approved by FDA too later in May 2006, nabilone, an oral-administered drug is an analogue of dronabinol.  The significant difference between cannabinoids and other existent antiemetic drugs is cannabinoid's mechanism which might involve an endogenous cannabinoid system within the emetic circuits. Thus, it can be used as auxiliary or to improve the effect of other drugs for refractory patients. 
Marijuana acts as analgesic though few possible mechanisms. By giving patients peripherally-restricted cannabinoid agonists, inflammatory pain can be reduced without causing any psychotropic effects because the central CB1 receptors are not activated. A study by Fride et al. (2004) shows that inflammatory pain response induced by formalin is greatly lessened when the cannabinoid receptors are chemically activated.  It is also found that CB2 receptor-selective agonists increase the tolerance for pain but do not affect other non-inflamed tissue.  Inhibiting the metabolism of endocannabinoid can also be effective in treating inflammatory pain.  In a randomised, placebo-controlled study involving 50 patients, half of them were asked to smoke cigarettes containing marijuana thrice a day for 5 days while the other half smoked placebo cigarettes. The results show the effectiveness of marijuana in reducing pain because 35% of those who smoked marijuana cigarettes reported alleviation of neuropathic pain while only 17% in the placebo group experienced so.  Even though non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used analgesic, high dosage of the drug is found to have adverse effects in the gastrointestinal and cardiovascular systems. This can be overcome by incorporating cannabinoids agonists into NSAID treatment because the activation of cannabinoid receptor can enhance its analgesic effect. 
Adverse effects of marijuana
Respiratory system disease
The risk of developing lung cancer from marijuana use is often associated with the smoking of marijuana. Tar is four times more likely to deposit in the lungs of marijuana smoker than tobacco smoker, given a cigarette of similar weight because marijuana cigarettes usually do not have filters and marijuana smokers tend to inhale more deeply and in larger puff volume.  Some party might argue that marijuana can be administered by other routes but the active ingredient of marijuana, cannabinoid is highly lipid-soluble, which makes it less effective to be taken orally or intravenously. Orally-administered marijuana takes 30-60 minutes to show its effects while the onset of action for smoked marijuana is rapid because it reaches the alveoli directly and diffuses into the systemic circulation.  A recent study shows that the risk of lung cancer rises by 8% when one smokes marijuana for one joint-year (365 joints or filled pipes). Â  It also reveals that the histological changes in the tracheobranchial epithelium of caused by few cannabis joints are equivalent to that of 20-30 tobacco cigarettes.  Tashkin (2005) also stressed that exposure to THC causes unregulated growth of epithelial cells which leads to chronic cough and inability of cilia to remove foreign materials. 
Acute cardiovascular effects
Activation of CB1 and CB2 receptors in the cardiac endocannabinoid system is identified as the cause of atherosclerosis due to endothelial dysfunction.  Smoking of marijuana causes acute cardiovascular physiology such as dose-dependent increase in heart rate, mild hypertension and decrease in exercise tolerant.  Consequently, only users with history of angina will experience chest pain due to the overworked heart.  The relationship between occurrence of palpitation and the use of marijuana is confirmed in a study involving more than 6700 subjects. 
There are also some evidence showing the side effects of marijuana on body systems like neoplastic, musculoskeletal, ocular, urological, reproductive and nervous system. 
If marijuana is approved as medicine, it might be abused as recreational drug like what happens in the case of opiates. Drug tolerance and dependence can develop if marijuana is used frequently. A person addicted to marijuana will experience depression, anxiety and disturbance in mood which indirectly lead to high suicide rate.  Driving under the influence of marijuana also put the lives of other road users at risk because of the physical and psychological effects produced. 
Even though there are some unwanted effects of marijuana use, it is a strong candidate as anticonvulsant, antiemetic, analgesic and muscle relaxant drug. Plantation of marijuana should be approved for research purposes only. Funded and controlled studies can be carried out to further discover its therapeutic effects as well as acute and long-term adverse effects. Studies should also emphasise on the interactions between different cannabinoids so as to identify components for more effective use of the drug. Once findings are matured to legalise marijuana, strict legislation should be implemented and enforced to prevent misuse of the drug. In short, marijuana has great potential in pharmaceutical values and will surely benefit mankind if used under control for medical purposes.