The answer to your question is in the following order:

Firstly, the use of narcotics is undoubtedly forbidden; because on one hand it causes serious and ruinous injuries to the body, whereas God has said: ﴿وَلَا تُلْقُوا بِأَيْدِيكُمْ إِلَى التَّهْلُكَةِ﴾[1]; “Do not throw yourselves with your own hands into destruction” and on the other hand it is considered a clear example of wasting the wealth, whereas God has said: ﴿وَلَا تُبَذِّرْ تَبْذِيرًا ۝ إِنَّ الْمُبَذِّرِينَ كَانُوا إِخْوَانَ الشَّيَاطِينِ ۖ وَكَانَ الشَّيْطَانُ لِرَبِّهِ كَفُورًا﴾[2]; “And do not waste (your wealth); because those who waste (the wealth) are brothers of satans, and satan is so ungrateful toward his Lord”; as one of our companions informed us, he said:

«سَمِعْتُ الْمَنْصُورَ الْهاشِمِيَّ الْخُراسانِيَّ يَقُولُ: ما كانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ يَشْرَبُ تِرْياكًا أَوْ يَتَعَلَّقُ تَمِيمَةً أَوْ يَقُولُ الشِّعْرَ مِنْ قِبَلِ نَفْسِهِ»; “I heard his Honor Mansoor Hashemi Khorasani saying: The Messenger of God peace and blessings of God be upon him and his family, did not use opium and did not wear amulet and did not compose poem by himself”.

And another of our helpers informed us, he said:

«سَأَلْتُهُ عَنِ التِّرْياكِ فَقالَ: إِنَّهُ كَالْخَمْرِ وَالْمَيْسِرِ فِيهِمَا إِثْمٌ كَبِيرٌ وَمَنَافِعُ لِلنَّاسِ وَإِثْمُهُمَا أَكْبَرُ مِنْ نَفْعِهِمَا، فَاجْتَنِبُوهُ لَعَلَّكُمْ تُفْلِحُونَ! قُلْتُ: إِنَّ مِنَ الْفُقَهاءِ مَنْ يَسْتَعْمِلُهُ! قالَ: ماذا تُرِيدُ مِنَ الْفُقَهاءِ؟! وَهَلِ الْفُقَهاءُ إِلّا رِجالٌ مِنَ النّاسِ؟!»; “I asked his Honor about opium, so he said: Indeed, it is like Khamr[3] and gambling, in which there is a great sin and benefits for people, and their sin is greater than their benefit, then avoid it, May you gain salvation! I said: There are some jurists who use it! He said: What do you want from the jurists?! Are the jurists except a number of people?!”

Secondly, there is no room for consideration and complication in the forbiddenness of using tobacco, like the forbiddenness of using narcotics; because its use, like the use of narcotics, is also the source of deadly diseases and an example of wasting the wealth; as one of our companions informed us, he said:

«سَأَلْتُ الْمَنْصُورَ عَنِ الْبَنْجِ فَقالَ: ذَاكَ مِنْ إِخْوانِها -يَعْنِي الْخَمْرَ! ثُمَّ قالَ: مَنْ أَخَذَ سِيجارًا فَقَدْ أَخَذَ جَمْرَةً مِنَ النّارِ! قُلْتُ: قَبَّحَ اللَّهُ إِمامَ قَوْمٍ قَدْ فُتِنَ بِالْأَنابِيبِ! فَتَأَمَّلَ قَلِيلًا ثُمَّ قالَ: دَعْ عَنْكَ هَذا»; “I asked his Honor Mansoor about hashish[4], so he said: This is one of its brothers - that is, Khamr[5]! Then he said: Whoever holds a cigarette in his hand, he has indeed held a flame from the fire (of hell) in his hand! I said: May God deform the Imam of a people who is fascinated by tobacco pipes! His Honor pondered a little and then said: Leave this (matter)”.

And another of our helpers informed us, he said:

«سَمِعْتُ خَيْرَ مَنْ رَأَيْتُهُ يَقُولُ: التَّدْخِينُ لَذَّةُ أَصْحابِ النّارِ وَسَمِعْتُهُ يَنْهَى عَنِ الصَّلاةِ خَلْفَ مَنْ يَسْتَعْمِلُ السِّيجارَ»; “I heard his Honor saying: Smoking is the pleasure of the people of the fire, and I heard that he forbids praying behind someone who smokes”.

And another of our helpers informed us, he said:

«رَأَى رَجُلًا يُدَخِّنُ فَقالَ لَهُ: أَيُعْجِبُكَ الدُّخانُ؟ قالَ: نَعَمْ، قالَ: ﴿فَارْتَقِبْ يَوْمَ تَأْتِي السَّمَاءُ بِدُخَانٍ مُبِينٍ ۝ يَغْشَى النَّاسَ ۖ هَذَا عَذَابٌ أَلِيمٌ﴾! فَأَلْقَى الرَّجُلُ سِيجارَهُ لَمّا سَمِعَ هَذا وَقالَ: أَسْتَغْفِرُ اللَّهَ وَأَتُوبُ إِلَيْهِ»; “His Excellency saw a man (holding a cigarette and) smoking, so he said to him: Do you like smoke? He said: Yes, he said: ‘Then wait for the day when the sky appears smoky; It engulfs people, it is a painful punishment’[6]! When the man heard this, he threw down his cigarette and said: I ask God for forgiveness and I repent toward Him”!

Thirdly, from what has been said, it is understood that buying and selling narcotics and tobacco is not permissible; because the rule in Islam is the forbiddenness of buying and selling anything that is forbidden to use; as one of our companions informed us, he said:

«سَمِعْتُ الْمَنْصُورَ يَقُولُ: ثَمَنُ الْكَلْبِ الَّذِي يُعْبَثُ بِهِ سُحْتٌ وَثَمَنُ الدُّخانِ سُحْتٌ»; “I heard his Honor Mansoor saying: The money of a dog with which one plays is forbidden, and the money of smoke is forbidden”.

And some others of our helpers informed us, they said:

«تَحاكَمَ إِلَيْهِ رَجُلانِ يَخْتَصِمانِ فَقالَ أَحَدُهُما: إِنَّ هَذا دَفَعَ إِلَيَّ حَشِيشًا فَشَرِبْتُهُ ثُمَّ جاءَنِي يَطْلُبُ أَجْرَهُ وَغالَى! فَقالَ الْآخَرُ: ما وَهَبْتُهُ لَهُ وَإِنَّما بِعْتُهُ! فَغَضِبَ وَقالَ: إِنَّ أَحَدَكُمْ لَيَسْقِي أَخاهُ سَمًّا لِيَقْتُلَهُ ثُمَّ يَأْتِيهِ يَطْلُبُ أَجْرَهُ؟! لا أَجْرَ لَهُ وَلا كَرامَةَ»; “Two men, arguing with each other, brought the arbitration to his Honor, so one of them said: This man gave me hashish and I used it, then he came to me and demanded its price from me and raised the price! The other man said: I did not give it to him, rather I sold it! So his Honor got angry and said: Indeed, one of you gives poison to his brother to kill him and then he comes to him and demands its price?! There is no price for him and has no value”!

Therefore, the one who sells narcotics and tobacco does not deserve their price, and if he gets their price, he has taken something forbidden and has eaten people’s wealth falsely, whereas God has said: ﴿يَا أَيُّهَا الَّذِينَ آمَنُوا لَا تَأْكُلُوا أَمْوَالَكُمْ بَيْنَكُمْ بِالْبَاطِلِ﴾[7]; “O you who believed! Do not eat each other’s wealth among yourselves falsely”; as giving their price to him by buyer is not permissible; because God has said: ﴿وَلَا تُؤْتُوا السُّفَهَاءَ أَمْوَالَكُمُ الَّتِي جَعَلَ اللَّهُ لَكُمْ قِيَامًا﴾[8]; “And do not give your wealth, which God has granted you as a support, to the fools”; rather, it is not unlikely that the major sellers and buyers of such materials are corruptors on earth and worthy of the punishment of Muharibs[9]; because the deadly consequences of the spread of these poisonous materials among Muslims are not hidden, to the extent that one can consider attempting it as attempting premeditated murder, and God is Aware of everything.