I have prayed the prayer of salvation many times in my life.  I  truly believe Christ died for my sins.  I was reading 1 John 3:7-10 last night and I am now unsure if I am a child of God.  I am constantly sinning.  I
smoke, do occasional drugs and do not always love my neighbor, to name a few.  I have never been transformed into what the bible teaches.  I feel like I am hopeless and from the devil.  What do I do? 

Dear Friend:   It sounds to me that you have not experienced truly committing your life to Jesus Christ.  Or maybe you did trust Jesus as Savior and Lord once and found some victory over your sin, but, fell back into old patterns of sin & temptation.   Paul wrote to people like you, "backslidden Christians" in Corinth who were quarreling and  committing sexual sins.   The following verses address "worldly" Corinthians as brothers and in the case of the man caught in incest..Paul states that his spirit will be saved in the day of the Lord: 
1 Cor 3:1-3   Brothers, I could not address you as spiritual but as worldly-- mere infants in Christ. 2 I gave you milk, not solid food, for you were not yet ready for it. Indeed, you are still not ready.  3 You are still worldly. For since there is jealousy and quarreling among you, are you not worldly?  Are you not acting like mere men?  (NIV) 
1 Cor 5:1-5  It is actually reported that there is sexual immorality among you, and of a kind that does not occur even among pagans...  5 hand this man over to Satan, so that the sinful nature may be destroyed and his spirit saved on the day of the Lord.  (NIV)

There are many other passages in Scripture which exhort & talk about Christians who are living sinful lives.  These Christians are quenching the Holy Spirit.  They are truly saved and going to heaven but they are grieving the Holy Spirit.  We Christians can actually limit the work of the Holy Spirit in our lives when we let our sinful tendencies control us.  Eph 4:30-32 says: And do not grieve the Holy Spirit of God, with whom you were sealed for the day of redemption.  31 Get rid of all bitterness, rage and anger, brawling and slander, along with every form of malice.  32 Be kind and compassionate to one another, forgiving each other, just as in Christ God forgave you. (NIV) 
I believe you are experiencing a "backslidden" state in your life. You are grieving the Holy Spirit.  You are right to question your faith and say "Am I really a Christian if I am not showing the fruit of the Holy Spirit consistently.  Take heart.  You know whether you made a genuine committment to Christ at one time in your life and are totally trusting Him and Him alone for your salvation. 
We as Christians are tempted by the world, the flesh and the Devil.  But  we have the choice to surrender our wills and lives to Christ so the Holy Spirit can take control. 
                  Eph 5:18 says: Do not get drunk on wine, which leads to debauchery.  Instead, be filled with the Spirit.  (NIV) 
                  You have a choice: you can decide to let Christ control your life or decide to continue controlling your life on your own. If you continue controlling your life, you will stay stuck in sin and never be free.  Since you are involved with drugs you are giving the devil "opportunity" in your life. Drugs along with other similar addictive sins are a "snare".   If you really want to be free, you need to get serious about your faith.   Ask Christ to take over the "throne" of your life.   Surrender yourself to Him, asking for forgiveness and a complete change in the direction of your life.   Give Him the control, doing it daily. 
Get into a Christian A.A. support group if possible (see the list of resources below).  Ask your pastor or elders for prayer. Seek out a small group Bible study for accountability, new Christian friends
and prayer.  You'll never regret turning your back on sin and turning back to Christ.  As a Christian you will always be tormented by disobeying God & living in sin.  Because you are a Christian and God wants you to glorify Him with your life, He may decide it is time to chastise you. 
There is nothing like living fully for Christ.  When you walk with Christ wholeheartedly you will experience victory over sin, His love, presence, power, peace and purpose.   There is nothing like living for
Christ. He is the living water and will satisfy your needs.  Your needs will never be satisfied by drugs, or any other sinful way of living.  These verses talk about the experience you will have as you grow in Christ. 
John 15:1-2  "I am the true vine, and my Father is the gardener.  2 He cuts off every branch in me that bears no fruit, while every branch that
does bear fruit he prunes so that it will be even more fruitful."
John 15:5  "I am the vine; you are the branches. If a man remains in me and I in him, he will bear much fruit; apart from me you can do nothing."
John 16:24 "Until now you have not asked for anything in my name. Ask and you will receive, and your joy will be complete."
John 16:33 "I have told you these things, so that in me you may have peace. In this world you will have trouble. But take heart! I have overcome the world."
John 16:27 "No, the Father himself loves you because you have loved me and have believed that I came from God." (NIV)

You need to investigate why you keep going back to drugs.  Maybe you are struggling with low self-esteem, or feeling like a failure.   You need an A.A. support group or counseling. Please contact AACC for a referral to a professional in your area.
Please take some action.  The life your living now is self-destructive besides being disobedient to God.    Take heart though.  With Christ there is freedom & forgiveness:
I Jn 1:9 If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness. 
John 8:36 So if the Son sets you free, you will be free indeed.
Rom 6:18 You have been set free from sin and have become slaves to righteousness. 
Rom 6:22-23 But now that you have been set free from sin and have become slaves to God, the benefit you reap leads to holiness, and the result is eternal life.  23 For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord. (NIV)
I believe that it is a good sign that you are convicted about your sins.  The Holy Spirit is trying to draw you back to Christ.   The verses you quoted from 1 John are a warning though that when a person consistently sins, he/she needs to evaluate his/her spiritual condition and standing before God.  I have printed out the verses here:
I Jn 3:7-10  Dear children, do not let anyone lead you astray. He who does what is right is righteous, just as he is righteous.
8 He who does what is sinful is of the devil, because the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the devil's work.  9 No one who is born of God will continue to sin, because God's seed remains in him; he cannot go on sinning, because he has been born of God.  10 This is how we know who the children of God are and who the children of the devil are: Anyone who does not do what is right is not a child of God; nor is anyone who does not love his brother.  (NIV)  
Check out this faq on faith  to consider more about how  to know Christ personally.
 
Please also check out the following resources, and the list of support groups, hotlines and helplines on our web site: 
Alcohol hotline:    1-800-ALC-OHOL 
     Alcohol & Drug helpline: 1-800-821-Help
     Alcoholics for Christ:    1-800-441-7877 
     Email: al4christ@globalbiz.net 
     Alcoholics Victorious:  1-800-624-5156 
     Cocaine helpline:  1-800-COC-AINE 
Christian Recovery: 
    Christian Recovery International
    National Association for Christian Recovery 
    His Mansion: 1-603-464-5555 personnel@hismansion.com (for youth)
     Overcomers Outreach, Inc: 1-800-310-3001; 1-714-491-3000
       Anaheim, CA
    AACC for a referral to a counseling professional in your area.
    Substance Abuse & Mental Health Services Administration 
(an agency of the U.S. Department of Health & Human Services)

God bless you! Lynette J. Hoy, NCC, LCPC