Science - Prohibition of drinking blood
Consuming animal or human blood poses significant health hazards, including the potential transmission of bloodborne illnesses. This practice is strongly discouraged by medical professionals. Paradoxically, while blood is vital for human survival, it is toxic to drink. Regular consumption of blood can result in severe illness and introduce various infections into one's own system. The peril to human health lies in the presence of hazardous viruses within blood. By exposing ourselves to another person's blood, we potentially expose ourselves to infections that reside in the bloodstream. Even a small amount of contaminated blood can transmit bloodborne diseases such as HIV, hepatitis B, or hepatitis C. Although syphilis is more commonly transmitted through sexual contact, it is also possible to contract it by exposing oneself to another person's blood.
Furthermore, blood harbors numerous toxins that, if consumed, can accumulate within the body, posing a significant health risk. Interestingly enough, although blood is vital when confined to its rightful places like the heart and vessels, it takes on a completely different nature when ingested. It's important to note that all toxins have varying doses, and just as a minuscule amount of poison may not necessarily harm you, the more blood you consume, the greater the danger becomes.
The high iron content in blood, coupled with the body's difficulty in eliminating excess iron, puts any creature regularly consuming blood at risk of iron overdose. While iron is essential for all living beings, excessive amounts can be toxic. This condition, known as haemochromatosis, can lead to a wide range of diseases and complications, including liver damage, fluid buildup in the lungs, dehydration, low blood pressure, and nervous disorders. Gradually, the consumption of blood and blood products manifests various health issues.
Qur'an - Prohibition of drinking blood
In verses 2:173, 5:3, and 6:145, blood is listed as one of the forbidden substances to drink in Islam. This prohibition was established over 1400 years ago, a time when the concept of microbes was yet unknown to people. Interestingly, the Arab culture of that era involved the consumption of camel blood prior to Islam. Even today, certain regions in southeast Asia continue the practice of including blood from specific animals in their food, sometimes even consuming it raw. It seems that either people are unaware of the scientific and medical warnings, or they simply choose to disregard them. Often, the justification given is "We have been doing this for years," a familiar refrain used to defend other harmful habits, such as smoking and drinking.
Please note that drinking blood is also prohibited in the Bible (e.g. Leviticus 7:26). Majority of Jews still follow this rule but Christians confusingly claim that rules were changed after early Christianity.
إِنَّمَا حَرَّمَ عَلَيْكُمُ ٱلْمَيْتَةَ وَٱلدَّمَ وَلَحْمَ ٱلْخِنزِيرِ وَمَآ أُهِلَّ بِهِۦ لِغَيْرِ ٱللَّهِ فَمَنِ ٱضْطُرَّ غَيْرَ بَاغٍ وَلَا عَادٍ فَلَآ إِثْمَ عَلَيْهِ إِنَّ ٱللَّهَ غَفُورٌ رَّحِيمٌ
He has only forbidden to you carrion, blood, the flesh of swine, and that which has been dedicated to other than Allah. But whoever is forced [by necessity], neither desiring [it] nor transgressing [its limit], there is no sin upon him. Indeed, Allah is Forgiving and Merciful. 2:173
حُرِّمَتْ عَلَيْكُمُ ٱلْمَيْتَةُ وَٱلدَّمُ وَلَحْمُ ٱلْخِنزِيرِ وَمَآ أُهِلَّ لِغَيْرِ ٱللَّهِ بِهِۦ وَٱلْمُنْخَنِقَةُ وَٱلْمَوْقُوذَةُ وَٱلْمُتَرَدِّيَةُ وَٱلنَّطِيحَةُ وَمَآ أَكَلَ ٱلسَّبُعُ إِلَّا مَا ذَكَّيْتُمْ وَمَا ذُبِحَ عَلَى ٱلنُّصُبِ وَأَن تَسْتَقْسِمُوا۟ بِٱلْأَزْلَـٰمِ ذَٰلِكُمْ فِسْقٌ ٱلْيَوْمَ يَئِسَ ٱلَّذِينَ كَفَرُوا۟ مِن دِينِكُمْ فَلَا تَخْشَوْهُمْ وَٱخْشَوْنِ ٱلْيَوْمَ أَكْمَلْتُ لَكُمْ دِينَكُمْ وَأَتْمَمْتُ عَلَيْكُمْ نِعْمَتِى وَرَضِيتُ لَكُمُ ٱلْإِسْلَـٰمَ دِينًا فَمَنِ ٱضْطُرَّ فِى مَخْمَصَةٍ غَيْرَ مُتَجَانِفٍ لِّإِثْمٍ فَإِنَّ ٱللَّهَ غَفُورٌ رَّحِيمٌ
Prohibited to you are dead animals, blood, the flesh of swine, and that which has been dedicated to other than Allah , and [those animals] killed by strangling or by a violent blow or by a head-long fall or by the goring of horns, and those from which a wild animal has eaten, except what you [are able to] slaughter [before its death], and those which are sacrificed on stone altars, and [prohibited is] that you seek decision through divining arrows. That is grave disobedience. This day those who disbelieve have despaired of [defeating] your religion; so fear them not, but fear Me. This day I have perfected for you your religion and completed My favor upon you and have approve
d for you Islam as religion. But whoever is forced by severe hunger with no inclination to sin - then indeed, Allah is Forgiving and Merciful 5:3
قُل لَّآ أَجِدُ فِى مَآ أُوحِىَ إِلَىَّ مُحَرَّمًا عَلَىٰ طَاعِمٍ يَطْعَمُهُۥٓ إِلَّآ أَن يَكُونَ مَيْتَةً أَوْ دَمًا مَّسْفُوحًا أَوْ لَحْمَ خِنزِيرٍ فَإِنَّهُۥ رِجْسٌ أَوْ فِسْقًا أُهِلَّ لِغَيْرِ ٱللَّهِ بِهِۦ فَمَنِ ٱضْطُرَّ غَيْرَ بَاغٍ وَلَا عَادٍ فَإِنَّ رَبَّكَ غَفُورٌ رَّحِيمٌ
Say, "I do not find within that which was revealed to me [anything] forbidden to one who would eat it unless it be a dead animal or blood spilled out or the flesh of swine - for indeed, it is impure - or it be [that slaughtered in] disobedience, dedicated to other than Allah . But whoever is forced [by necessity], neither desiring [it] nor transgressing [its limit], then indeed, your Lord is Forgiving and Merciful." 6:145