In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
According to scientific studies, using marijuana is proven to be deleterious to mental and physical health.
The only exception would be medicinal use where there is no alternative; in which case it is permissible under the rule of ‘necessity lifts the prohibitions.’ Allah says,
“Those who shall follow the [last] Messenger, the unlettered Prophet, whom they shall find described in the Torah and Gospel that is with them, who enjoins what is right, and forbids them what is wrong, and makes good things lawful for them, and forbids them bad things (khaba’ith), and relieves them of their burden and the shackles that were upon them. Thus, those who believe in him, honor him, help him, and follow the light that has been sent down with him; it is they who shall prosper.” (Al-A`raf 7: 157)
The word khaba’ith as used in the above verse refers all actions including consumption of foods and drinks that are forbidden because they are deemed filthy and impure.
It is clear from another verse where Allah forbids the use of intoxicants:
“O you who believe! Intoxicants, gambling, and idols, and divining arrows are, but filthy (and loathsome) practices, of Satan’s work. So shun it, that haply you may prosper.” (Al-Ma’idah 5:90)
The Prophet (peace be upon him) said, “Everything that causes intoxication is wine, and hence all intoxicants are also forbidden.” (An-Nasa’i)
Furthermore, while explaining the reasons for banning intoxicants and gambling, Allah says in the Qur’an:
“They will ask you about intoxicants and games of chance. Say: “In both, there is great evil as well as some benefits for man, but the evil which they cause is greater than the benefit which they bring.” (Al-Baqarah 2: 219)
Based on this, the rule of the Shari`ah is that a thing which has some benefits while having greater harm, it should be forbidden. This rule applies to wine, alcohol and all forms of intoxicants, including the use of cannabis.
Let me cite here from the Government of Canada (health-Canada/services):
“While cannabis may make you feel relaxed and happy, your body and brain may also experience effects that are: negative, unwanted, unpleasant, and some of the short-term effects on your brain can include…impaired ability to: remember; concentrate; pay attention; react quickly; anxiety, fear or panic.”
“Short-term effects on your body can also include: if smoking damaged blood vessels caused by the smoke decreased blood pressure, which can cause people to faint increased heart rate, which can be dangerous for people with heart conditions and can lead to an increased risk of heart attack.”
“Cannabis use can also result in psychotic episodes characterized by paranoia; delusions; hallucinations The long-term effects of cannabis on your brain can include an increased risk of addiction. Long-term cannabis use can also harm your: memory; concentration; intelligence (IQ); ability to think and make decisions.
Other long-term effects of smoking cannabis are similar to the effects
of smoking tobacco. These effects can include risks to lung health,
such as bronchitis; lung infections; chronic (long-term) cough; increased mucus buildup in the chest.” (Health effects of cannabis)
It is rather easy for us to conclude that the Quranic principle stated above prohibiting intoxicants and gambling applies to use of marijuana, as well.
Therefore, no Muslim can use cannabis unless he is forced to consume it for medical reasons – under the strict prescription of a trained medical practitioner.
Almighty Allah knows best.