Can he use medication which may cause his death to reduce pain?
Question

                Two years ago I had a surgery to remove a tumor from my maxillary sinus. Since that time, I have continuous sinus and facial pain and I take pain medication. The pain did not subside after taking several medicines. Once or twice a week, I have to delay my farad salat by few hours when level of pain is high. Recently my physician has prescribed a medicine to reduce pain and according to him it has high risk of fatality, one in a thousand. My instinct tells me that taking this medicine is not acceptable, because if I die of it, it would be like committing suicide. Is taking a high risk medicine, which can kill a patient when his life is not in danger, acceptable in our religion?.
Praise be to Allah.
    We ask Allaah to grant you healing and good health. 
It is not permissible for 
    the Muslim whom Allaah is testing with sickness to take something that will 
    definitely or will most likely harm him. He is commanded to protect his body 
    and it is not permissible for him to neglect the blessing of the physical 
    faculties that Allaah has bestowed upon him. How can he neglect himself? 

    One of the basic principles of Islamic sharee’ah is: “A 
    harmful thing cannot be removed by something like it (i.e., something else 
    that is also harmful).” Based on this, it is haraam to use as medicine 
    something that will cause greater harm than the disease itself. 

    See: Ahkaam al-Jaraahah al-Tibbiyyah, p. 124, by 
    Shaykh Dr. Muhammad ibn Muhammad al-Mukhtaar al-Shanqeeti. 

    Patience in putting up with pain and seeking the reward of 
    Allaah are things that will benefit the Muslim in the Hereafter and increase 
    his reward.  

    It was narrated from Abu Sa’eed al-Khudri and Abu Hurayrah 
    that the Prophet  (peace and blessings of Allaah be upon him) said: “No 
    tiredness, exhaustion, worry, grief, distress or harm befalls a believer in 
    this world, not even a thorn that pricks him, but Allaah expiates some of 
    his sins thereby.” Narrated by al-Bukhaari, 5318 and Muslim, 2573.  

    Read the story of this great women and how she was afflicted 
    by sickness – with all its pain – but she chose to bear it with patience in 
    return for the great reward, which is admittance to Paradise. 

    It was narrated that ‘Ata’ ibn Abi Rabaah said: Ibn ‘Abbaas 
    said to me: Shall I not show you a woman who is one of the people of 
    Paradise? He said: Yes. He said: This black woman came to the Prophet (peace 
    and blessings of Allaah be upon him) and said: “I suffer from epilepsy and I 
    become uncovered. Pray to Allaah for me.” He said: “If you wish, you can be 
    patient and Paradise will be yours, or if you wish I will pray to Allaah to 
    heal you.” She said, “I will be patient.” Then she said: “But I become 
    uncovered. Pray to Allaah that I will not become uncovered.” So he prayed 
    for her.

    Narrated by al-Bukhaari, 5652; Muslim, 2576.  

    Some doctors have stated that taking tranquillizers may cause 
    a great deal of harm and lead to serious complications. 

    Some specialists have said that it is possible to reduce pain 
    through a nutritional program and an exercise regime, and other methods… You 
    should consult more than one doctor; perhaps with another specialist you 
    will find an answer that the one who told you to take that dangerous 
    medication does not know about. 

    But first and foremost, you have to be patient and accept the 
    decree of Allaah; make a lot of du’aa’ and ask Allaah for good health, for 
    Allaah says (interpretation of the meaning): 

    “Who responds to the distressed one, when he calls on Him, 
    and Who removes the evil”

    [al-Naml 27:62]
We ask Allaah to take 
    away your pain, and to decree reward for you, and to grant you wellbeing in 
    your spiritual and worldly affairs, and to protect you and take care of 
    you. 

    And Allaah is the Source of strength.